[Default] update isAdditionalPropertiesTrue tag to cover more types (#16227)

* enhance additional properties support

* update samples

* update tests

* add more tests

* update samples

* fix samples

samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/AdditionalPropertiesAnyType.java

@@ -79,6 +79,50 @@ public class AdditionalPropertiesAnyType {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesAnyType instance itself
+   */
+  public AdditionalPropertiesAnyType putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -90,12 +134,13 @@ public class AdditionalPropertiesAnyType {
       return false;
     }
     AdditionalPropertiesAnyType additionalPropertiesAnyType = (AdditionalPropertiesAnyType) o;
-    return Objects.equals(this.name, additionalPropertiesAnyType.name);
+    return Objects.equals(this.name, additionalPropertiesAnyType.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesAnyType.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -103,6 +148,7 @@ public class AdditionalPropertiesAnyType {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesAnyType {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -143,14 +189,6 @@ public class AdditionalPropertiesAnyType {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesAnyType is not found in the empty JSON string", AdditionalPropertiesAnyType.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesAnyType.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesAnyType` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -172,6 +210,23 @@ public class AdditionalPropertiesAnyType {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesAnyType value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -179,7 +234,28 @@ public class AdditionalPropertiesAnyType {
            public AdditionalPropertiesAnyType read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesAnyType instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/AdditionalPropertiesArray.java

@@ -80,6 +80,50 @@ public class AdditionalPropertiesArray {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesArray instance itself
+   */
+  public AdditionalPropertiesArray putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -91,12 +135,13 @@ public class AdditionalPropertiesArray {
       return false;
     }
     AdditionalPropertiesArray additionalPropertiesArray = (AdditionalPropertiesArray) o;
-    return Objects.equals(this.name, additionalPropertiesArray.name);
+    return Objects.equals(this.name, additionalPropertiesArray.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesArray.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -104,6 +149,7 @@ public class AdditionalPropertiesArray {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesArray {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -144,14 +190,6 @@ public class AdditionalPropertiesArray {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesArray is not found in the empty JSON string", AdditionalPropertiesArray.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesArray.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesArray` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -173,6 +211,23 @@ public class AdditionalPropertiesArray {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesArray value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -180,7 +235,28 @@ public class AdditionalPropertiesArray {
            public AdditionalPropertiesArray read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesArray instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/AdditionalPropertiesBoolean.java

@@ -79,6 +79,50 @@ public class AdditionalPropertiesBoolean {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesBoolean instance itself
+   */
+  public AdditionalPropertiesBoolean putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -90,12 +134,13 @@ public class AdditionalPropertiesBoolean {
       return false;
     }
     AdditionalPropertiesBoolean additionalPropertiesBoolean = (AdditionalPropertiesBoolean) o;
-    return Objects.equals(this.name, additionalPropertiesBoolean.name);
+    return Objects.equals(this.name, additionalPropertiesBoolean.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesBoolean.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -103,6 +148,7 @@ public class AdditionalPropertiesBoolean {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesBoolean {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -143,14 +189,6 @@ public class AdditionalPropertiesBoolean {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesBoolean is not found in the empty JSON string", AdditionalPropertiesBoolean.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesBoolean.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesBoolean` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -172,6 +210,23 @@ public class AdditionalPropertiesBoolean {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesBoolean value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -179,7 +234,28 @@ public class AdditionalPropertiesBoolean {
            public AdditionalPropertiesBoolean read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesBoolean instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/AdditionalPropertiesInteger.java

@@ -79,6 +79,50 @@ public class AdditionalPropertiesInteger {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesInteger instance itself
+   */
+  public AdditionalPropertiesInteger putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -90,12 +134,13 @@ public class AdditionalPropertiesInteger {
       return false;
     }
     AdditionalPropertiesInteger additionalPropertiesInteger = (AdditionalPropertiesInteger) o;
-    return Objects.equals(this.name, additionalPropertiesInteger.name);
+    return Objects.equals(this.name, additionalPropertiesInteger.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesInteger.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -103,6 +148,7 @@ public class AdditionalPropertiesInteger {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesInteger {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -143,14 +189,6 @@ public class AdditionalPropertiesInteger {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesInteger is not found in the empty JSON string", AdditionalPropertiesInteger.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesInteger.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesInteger` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -172,6 +210,23 @@ public class AdditionalPropertiesInteger {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesInteger value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -179,7 +234,28 @@ public class AdditionalPropertiesInteger {
            public AdditionalPropertiesInteger read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesInteger instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/AdditionalPropertiesNumber.java

@@ -80,6 +80,50 @@ public class AdditionalPropertiesNumber {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesNumber instance itself
+   */
+  public AdditionalPropertiesNumber putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -91,12 +135,13 @@ public class AdditionalPropertiesNumber {
       return false;
     }
     AdditionalPropertiesNumber additionalPropertiesNumber = (AdditionalPropertiesNumber) o;
-    return Objects.equals(this.name, additionalPropertiesNumber.name);
+    return Objects.equals(this.name, additionalPropertiesNumber.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesNumber.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -104,6 +149,7 @@ public class AdditionalPropertiesNumber {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesNumber {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -144,14 +190,6 @@ public class AdditionalPropertiesNumber {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesNumber is not found in the empty JSON string", AdditionalPropertiesNumber.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesNumber.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesNumber` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -173,6 +211,23 @@ public class AdditionalPropertiesNumber {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesNumber value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -180,7 +235,28 @@ public class AdditionalPropertiesNumber {
            public AdditionalPropertiesNumber read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesNumber instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/AdditionalPropertiesObject.java

@@ -80,6 +80,50 @@ public class AdditionalPropertiesObject {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesObject instance itself
+   */
+  public AdditionalPropertiesObject putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -91,12 +135,13 @@ public class AdditionalPropertiesObject {
       return false;
     }
     AdditionalPropertiesObject additionalPropertiesObject = (AdditionalPropertiesObject) o;
-    return Objects.equals(this.name, additionalPropertiesObject.name);
+    return Objects.equals(this.name, additionalPropertiesObject.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesObject.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -104,6 +149,7 @@ public class AdditionalPropertiesObject {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesObject {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -144,14 +190,6 @@ public class AdditionalPropertiesObject {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesObject is not found in the empty JSON string", AdditionalPropertiesObject.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesObject.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesObject` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -173,6 +211,23 @@ public class AdditionalPropertiesObject {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesObject value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -180,7 +235,28 @@ public class AdditionalPropertiesObject {
            public AdditionalPropertiesObject read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesObject instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/model/AdditionalPropertiesString.java

@@ -79,6 +79,50 @@ public class AdditionalPropertiesString {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesString instance itself
+   */
+  public AdditionalPropertiesString putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -90,12 +134,13 @@ public class AdditionalPropertiesString {
       return false;
     }
     AdditionalPropertiesString additionalPropertiesString = (AdditionalPropertiesString) o;
-    return Objects.equals(this.name, additionalPropertiesString.name);
+    return Objects.equals(this.name, additionalPropertiesString.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesString.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -103,6 +148,7 @@ public class AdditionalPropertiesString {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesString {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -143,14 +189,6 @@ public class AdditionalPropertiesString {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesString is not found in the empty JSON string", AdditionalPropertiesString.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesString.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesString` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -172,6 +210,23 @@ public class AdditionalPropertiesString {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesString value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -179,7 +234,28 @@ public class AdditionalPropertiesString {
            public AdditionalPropertiesString read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesString instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/AdditionalPropertiesAnyType.java

@@ -81,6 +81,50 @@ public class AdditionalPropertiesAnyType implements Parcelable {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesAnyType instance itself
+   */
+  public AdditionalPropertiesAnyType putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -92,12 +136,13 @@ public class AdditionalPropertiesAnyType implements Parcelable {
       return false;
     }
     AdditionalPropertiesAnyType additionalPropertiesAnyType = (AdditionalPropertiesAnyType) o;
-    return Objects.equals(this.name, additionalPropertiesAnyType.name);
+    return Objects.equals(this.name, additionalPropertiesAnyType.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesAnyType.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -105,6 +150,7 @@ public class AdditionalPropertiesAnyType implements Parcelable {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesAnyType {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -166,14 +212,6 @@ public class AdditionalPropertiesAnyType implements Parcelable {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesAnyType is not found in the empty JSON string", AdditionalPropertiesAnyType.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesAnyType.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesAnyType` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -195,6 +233,23 @@ public class AdditionalPropertiesAnyType implements Parcelable {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesAnyType value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -202,7 +257,28 @@ public class AdditionalPropertiesAnyType implements Parcelable {
            public AdditionalPropertiesAnyType read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesAnyType instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/AdditionalPropertiesArray.java

@@ -82,6 +82,50 @@ public class AdditionalPropertiesArray implements Parcelable {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesArray instance itself
+   */
+  public AdditionalPropertiesArray putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -93,12 +137,13 @@ public class AdditionalPropertiesArray implements Parcelable {
       return false;
     }
     AdditionalPropertiesArray additionalPropertiesArray = (AdditionalPropertiesArray) o;
-    return Objects.equals(this.name, additionalPropertiesArray.name);
+    return Objects.equals(this.name, additionalPropertiesArray.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesArray.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -106,6 +151,7 @@ public class AdditionalPropertiesArray implements Parcelable {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesArray {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -167,14 +213,6 @@ public class AdditionalPropertiesArray implements Parcelable {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesArray is not found in the empty JSON string", AdditionalPropertiesArray.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesArray.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesArray` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -196,6 +234,23 @@ public class AdditionalPropertiesArray implements Parcelable {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesArray value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -203,7 +258,28 @@ public class AdditionalPropertiesArray implements Parcelable {
            public AdditionalPropertiesArray read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesArray instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/AdditionalPropertiesBoolean.java

@@ -81,6 +81,50 @@ public class AdditionalPropertiesBoolean implements Parcelable {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesBoolean instance itself
+   */
+  public AdditionalPropertiesBoolean putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -92,12 +136,13 @@ public class AdditionalPropertiesBoolean implements Parcelable {
       return false;
     }
     AdditionalPropertiesBoolean additionalPropertiesBoolean = (AdditionalPropertiesBoolean) o;
-    return Objects.equals(this.name, additionalPropertiesBoolean.name);
+    return Objects.equals(this.name, additionalPropertiesBoolean.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesBoolean.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -105,6 +150,7 @@ public class AdditionalPropertiesBoolean implements Parcelable {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesBoolean {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -166,14 +212,6 @@ public class AdditionalPropertiesBoolean implements Parcelable {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesBoolean is not found in the empty JSON string", AdditionalPropertiesBoolean.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesBoolean.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesBoolean` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -195,6 +233,23 @@ public class AdditionalPropertiesBoolean implements Parcelable {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesBoolean value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -202,7 +257,28 @@ public class AdditionalPropertiesBoolean implements Parcelable {
            public AdditionalPropertiesBoolean read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesBoolean instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/AdditionalPropertiesInteger.java

@@ -81,6 +81,50 @@ public class AdditionalPropertiesInteger implements Parcelable {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesInteger instance itself
+   */
+  public AdditionalPropertiesInteger putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -92,12 +136,13 @@ public class AdditionalPropertiesInteger implements Parcelable {
       return false;
     }
     AdditionalPropertiesInteger additionalPropertiesInteger = (AdditionalPropertiesInteger) o;
-    return Objects.equals(this.name, additionalPropertiesInteger.name);
+    return Objects.equals(this.name, additionalPropertiesInteger.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesInteger.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -105,6 +150,7 @@ public class AdditionalPropertiesInteger implements Parcelable {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesInteger {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -166,14 +212,6 @@ public class AdditionalPropertiesInteger implements Parcelable {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesInteger is not found in the empty JSON string", AdditionalPropertiesInteger.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesInteger.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesInteger` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -195,6 +233,23 @@ public class AdditionalPropertiesInteger implements Parcelable {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesInteger value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -202,7 +257,28 @@ public class AdditionalPropertiesInteger implements Parcelable {
            public AdditionalPropertiesInteger read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesInteger instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/AdditionalPropertiesNumber.java

@@ -82,6 +82,50 @@ public class AdditionalPropertiesNumber implements Parcelable {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesNumber instance itself
+   */
+  public AdditionalPropertiesNumber putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -93,12 +137,13 @@ public class AdditionalPropertiesNumber implements Parcelable {
       return false;
     }
     AdditionalPropertiesNumber additionalPropertiesNumber = (AdditionalPropertiesNumber) o;
-    return Objects.equals(this.name, additionalPropertiesNumber.name);
+    return Objects.equals(this.name, additionalPropertiesNumber.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesNumber.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -106,6 +151,7 @@ public class AdditionalPropertiesNumber implements Parcelable {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesNumber {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -167,14 +213,6 @@ public class AdditionalPropertiesNumber implements Parcelable {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesNumber is not found in the empty JSON string", AdditionalPropertiesNumber.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesNumber.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesNumber` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -196,6 +234,23 @@ public class AdditionalPropertiesNumber implements Parcelable {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesNumber value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -203,7 +258,28 @@ public class AdditionalPropertiesNumber implements Parcelable {
            public AdditionalPropertiesNumber read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesNumber instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/AdditionalPropertiesObject.java

@@ -82,6 +82,50 @@ public class AdditionalPropertiesObject implements Parcelable {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesObject instance itself
+   */
+  public AdditionalPropertiesObject putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -93,12 +137,13 @@ public class AdditionalPropertiesObject implements Parcelable {
       return false;
     }
     AdditionalPropertiesObject additionalPropertiesObject = (AdditionalPropertiesObject) o;
-    return Objects.equals(this.name, additionalPropertiesObject.name);
+    return Objects.equals(this.name, additionalPropertiesObject.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesObject.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -106,6 +151,7 @@ public class AdditionalPropertiesObject implements Parcelable {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesObject {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -167,14 +213,6 @@ public class AdditionalPropertiesObject implements Parcelable {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesObject is not found in the empty JSON string", AdditionalPropertiesObject.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesObject.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesObject` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -196,6 +234,23 @@ public class AdditionalPropertiesObject implements Parcelable {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesObject value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -203,7 +258,28 @@ public class AdditionalPropertiesObject implements Parcelable {
            public AdditionalPropertiesObject read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesObject instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/model/AdditionalPropertiesString.java

@@ -81,6 +81,50 @@ public class AdditionalPropertiesString implements Parcelable {
     this.name = name;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the AdditionalPropertiesString instance itself
+   */
+  public AdditionalPropertiesString putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -92,12 +136,13 @@ public class AdditionalPropertiesString implements Parcelable {
       return false;
     }
     AdditionalPropertiesString additionalPropertiesString = (AdditionalPropertiesString) o;
-    return Objects.equals(this.name, additionalPropertiesString.name);
+    return Objects.equals(this.name, additionalPropertiesString.name)&&
+        Objects.equals(this.additionalProperties, additionalPropertiesString.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(name);
+    return Objects.hash(name, additionalProperties);
   }
 
   @Override
@@ -105,6 +150,7 @@ public class AdditionalPropertiesString implements Parcelable {
     StringBuilder sb = new StringBuilder();
     sb.append("class AdditionalPropertiesString {\n");
     sb.append("    name: ").append(toIndentedString(name)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -166,14 +212,6 @@ public class AdditionalPropertiesString implements Parcelable {
           throw new IllegalArgumentException(String.format("The required field(s) %s in AdditionalPropertiesString is not found in the empty JSON string", AdditionalPropertiesString.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!AdditionalPropertiesString.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `AdditionalPropertiesString` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("name") != null && !jsonObj.get("name").isJsonNull()) && !jsonObj.get("name").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `name` to be a primitive type in the JSON string but got `%s`", jsonObj.get("name").toString()));
@@ -195,6 +233,23 @@ public class AdditionalPropertiesString implements Parcelable {
            @Override
            public void write(JsonWriter out, AdditionalPropertiesString value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -202,7 +257,28 @@ public class AdditionalPropertiesString implements Parcelable {
            public AdditionalPropertiesString read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             AdditionalPropertiesString instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/Drawing.java

@@ -169,6 +169,50 @@ public class Drawing {
     this.shapes = shapes;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the Drawing instance itself
+   */
+  public Drawing putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -183,7 +227,8 @@ public class Drawing {
     return Objects.equals(this.mainShape, drawing.mainShape) &&
         Objects.equals(this.shapeOrNull, drawing.shapeOrNull) &&
         Objects.equals(this.nullableShape, drawing.nullableShape) &&
-        Objects.equals(this.shapes, drawing.shapes);
+        Objects.equals(this.shapes, drawing.shapes)&&
+        Objects.equals(this.additionalProperties, drawing.additionalProperties);
   }
 
   private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
@@ -192,7 +237,7 @@ public class Drawing {
 
   @Override
   public int hashCode() {
-    return Objects.hash(mainShape, shapeOrNull, nullableShape, shapes);
+    return Objects.hash(mainShape, shapeOrNull, nullableShape, shapes, additionalProperties);
   }
 
   private static <T> int hashCodeNullable(JsonNullable<T> a) {
@@ -210,6 +255,7 @@ public class Drawing {
     sb.append("    shapeOrNull: ").append(toIndentedString(shapeOrNull)).append("\n");
     sb.append("    nullableShape: ").append(toIndentedString(nullableShape)).append("\n");
     sb.append("    shapes: ").append(toIndentedString(shapes)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -253,14 +299,6 @@ public class Drawing {
           throw new IllegalArgumentException(String.format("The required field(s) %s in Drawing is not found in the empty JSON string", Drawing.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!Drawing.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `Drawing` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       // validate the optional field `mainShape`
       if (jsonObj.get("mainShape") != null && !jsonObj.get("mainShape").isJsonNull()) {
@@ -305,6 +343,23 @@ public class Drawing {
            @Override
            public void write(JsonWriter out, Drawing value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -312,7 +367,28 @@ public class Drawing {
            public Drawing read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             Drawing instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();

samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/model/NullableClass.java

@@ -410,6 +410,50 @@ public class NullableClass {
     this.objectItemsNullable = objectItemsNullable;
   }
 
+  /**
+   * A container for additional, undeclared properties.
+   * This is a holder for any undeclared properties as specified with
+   * the 'additionalProperties' keyword in the OAS document.
+   */
+  private Map<String, Object> additionalProperties;
+
+  /**
+   * Set the additional (undeclared) property with the specified name and value.
+   * If the property does not already exist, create it otherwise replace it.
+   *
+   * @param key name of the property
+   * @param value value of the property
+   * @return the NullableClass instance itself
+   */
+  public NullableClass putAdditionalProperty(String key, Object value) {
+    if (this.additionalProperties == null) {
+        this.additionalProperties = new HashMap<String, Object>();
+    }
+    this.additionalProperties.put(key, value);
+    return this;
+  }
+
+  /**
+   * Return the additional (undeclared) property.
+   *
+   * @return a map of objects
+   */
+  public Map<String, Object> getAdditionalProperties() {
+    return additionalProperties;
+  }
+
+  /**
+   * Return the additional (undeclared) property with the specified name.
+   *
+   * @param key name of the property
+   * @return an object
+   */
+  public Object getAdditionalProperty(String key) {
+    if (this.additionalProperties == null) {
+        return null;
+    }
+    return this.additionalProperties.get(key);
+  }
 
 
   @Override
@@ -432,7 +476,8 @@ public class NullableClass {
         Objects.equals(this.arrayItemsNullable, nullableClass.arrayItemsNullable) &&
         Objects.equals(this.objectNullableProp, nullableClass.objectNullableProp) &&
         Objects.equals(this.objectAndItemsNullableProp, nullableClass.objectAndItemsNullableProp) &&
-        Objects.equals(this.objectItemsNullable, nullableClass.objectItemsNullable);
+        Objects.equals(this.objectItemsNullable, nullableClass.objectItemsNullable)&&
+        Objects.equals(this.additionalProperties, nullableClass.additionalProperties);
   }
 
   private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
@@ -441,7 +486,7 @@ public class NullableClass {
 
   @Override
   public int hashCode() {
-    return Objects.hash(integerProp, numberProp, booleanProp, stringProp, dateProp, datetimeProp, arrayNullableProp, arrayAndItemsNullableProp, arrayItemsNullable, objectNullableProp, objectAndItemsNullableProp, objectItemsNullable);
+    return Objects.hash(integerProp, numberProp, booleanProp, stringProp, dateProp, datetimeProp, arrayNullableProp, arrayAndItemsNullableProp, arrayItemsNullable, objectNullableProp, objectAndItemsNullableProp, objectItemsNullable, additionalProperties);
   }
 
   private static <T> int hashCodeNullable(JsonNullable<T> a) {
@@ -467,6 +512,7 @@ public class NullableClass {
     sb.append("    objectNullableProp: ").append(toIndentedString(objectNullableProp)).append("\n");
     sb.append("    objectAndItemsNullableProp: ").append(toIndentedString(objectAndItemsNullableProp)).append("\n");
     sb.append("    objectItemsNullable: ").append(toIndentedString(objectItemsNullable)).append("\n");
+    sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
     return sb.toString();
   }
@@ -518,14 +564,6 @@ public class NullableClass {
           throw new IllegalArgumentException(String.format("The required field(s) %s in NullableClass is not found in the empty JSON string", NullableClass.openapiRequiredFields.toString()));
         }
       }
-
-      Set<Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
-      // check to see if the JSON string contains additional fields
-      for (Entry<String, JsonElement> entry : entries) {
-        if (!NullableClass.openapiFields.contains(entry.getKey())) {
-          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `NullableClass` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
-        }
-      }
         JsonObject jsonObj = jsonElement.getAsJsonObject();
       if ((jsonObj.get("string_prop") != null && !jsonObj.get("string_prop").isJsonNull()) && !jsonObj.get("string_prop").isJsonPrimitive()) {
         throw new IllegalArgumentException(String.format("Expected the field `string_prop` to be a primitive type in the JSON string but got `%s`", jsonObj.get("string_prop").toString()));
@@ -559,6 +597,23 @@ public class NullableClass {
            @Override
            public void write(JsonWriter out, NullableClass value) throws IOException {
              JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             obj.remove("additionalProperties");
+             // serialize additional properties
+             if (value.getAdditionalProperties() != null) {
+               for (Map.Entry<String, Object> entry : value.getAdditionalProperties().entrySet()) {
+                 if (entry.getValue() instanceof String)
+                   obj.addProperty(entry.getKey(), (String) entry.getValue());
+                 else if (entry.getValue() instanceof Number)
+                   obj.addProperty(entry.getKey(), (Number) entry.getValue());
+                 else if (entry.getValue() instanceof Boolean)
+                   obj.addProperty(entry.getKey(), (Boolean) entry.getValue());
+                 else if (entry.getValue() instanceof Character)
+                   obj.addProperty(entry.getKey(), (Character) entry.getValue());
+                 else {
+                   obj.add(entry.getKey(), gson.toJsonTree(entry.getValue()).getAsJsonObject());
+                 }
+               }
+             }
              elementAdapter.write(out, obj);
            }
 
@@ -566,7 +621,28 @@ public class NullableClass {
            public NullableClass read(JsonReader in) throws IOException {
              JsonElement jsonElement = elementAdapter.read(in);
              validateJsonElement(jsonElement);
-             return thisAdapter.fromJsonTree(jsonElement);
+             JsonObject jsonObj = jsonElement.getAsJsonObject();
+             // store additional fields in the deserialized instance
+             NullableClass instance = thisAdapter.fromJsonTree(jsonObj);
+             for (Map.Entry<String, JsonElement> entry : jsonObj.entrySet()) {
+               if (!openapiFields.contains(entry.getKey())) {
+                 if (entry.getValue().isJsonPrimitive()) { // primitive type
+                   if (entry.getValue().getAsJsonPrimitive().isString())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsString());
+                   else if (entry.getValue().getAsJsonPrimitive().isNumber())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsNumber());
+                   else if (entry.getValue().getAsJsonPrimitive().isBoolean())
+                     instance.putAdditionalProperty(entry.getKey(), entry.getValue().getAsBoolean());
+                   else
+                     throw new IllegalArgumentException(String.format("The field `%s` has unknown primitive type. Value: %s", entry.getKey(), entry.getValue().toString()));
+                 } else if (entry.getValue().isJsonArray()) {
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), List.class));
+                 } else { // JSON object
+                     instance.putAdditionalProperty(entry.getKey(), gson.fromJson(entry.getValue(), HashMap.class));
+                 }
+               }
+             }
+             return instance;
            }
 
        }.nullSafe();