diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java
index 68d6b129d0b..c15806bffa8 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java
@@ -615,6 +615,13 @@ public class JavaClientCodegen extends AbstractJavaCodegen
             supportingFiles.add(new SupportingFile("JSON.mustache", invokerFolder, "JSON.java"));
             supportingFiles.add(new SupportingFile("AbstractOpenApiSchema.mustache", modelsFolder, "AbstractOpenApiSchema.java"));
             forceSerializationLibrary(SERIALIZATION_LIBRARY_JACKSON);
+
+            // Composed schemas can have the 'additionalProperties' keyword, as specified in JSON schema.
+            // In principle, this should be enabled by default for all code generators. However due to limitations
+            // in other code generators, support needs to be enabled on a case-by-case basis.
+            // The flag below should be set for all Java libraries, but the templates need to be ported
+            // one by one for each library.
+            supportsAdditionalPropertiesWithComposedSchema = true;
         } else if (libRestEasy) {
             supportingFiles.add(new SupportingFile("JSON.mustache", invokerFolder, "JSON.java"));
             forceSerializationLibrary(SERIALIZATION_LIBRARY_JACKSON);
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java
index 18be680595d..b0ddd504929 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Drawing.java
@@ -30,9 +30,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 import com.fasterxml.jackson.annotation.JsonValue;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 import org.openapitools.client.model.Fruit;
 import org.openapitools.client.model.NullableShape;
 import org.openapitools.client.model.Shape;
@@ -55,7 +53,7 @@ import org.openapitools.client.ApiClient;
   Drawing.JSON_PROPERTY_SHAPES
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class Drawing extends HashMap<String, Fruit> {
+public class Drawing {
   public static final String JSON_PROPERTY_MAIN_SHAPE = "mainShape";
   @javax.annotation.Nullable
   private Shape mainShape;
@@ -245,8 +243,7 @@ public class Drawing extends HashMap<String, Fruit> {
         Objects.equals(this.shapeOrNull, drawing.shapeOrNull) &&
         equalsNullable(this.nullableShape, drawing.nullableShape) &&
         Objects.equals(this.shapes, drawing.shapes)&&
-        Objects.equals(this.additionalProperties, drawing.additionalProperties) &&
-        super.equals(o);
+        Objects.equals(this.additionalProperties, drawing.additionalProperties);
   }
 
   private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
@@ -255,7 +252,7 @@ public class Drawing extends HashMap<String, Fruit> {
 
   @Override
   public int hashCode() {
-    return Objects.hash(mainShape, shapeOrNull, hashCodeNullable(nullableShape), shapes, super.hashCode(), additionalProperties);
+    return Objects.hash(mainShape, shapeOrNull, hashCodeNullable(nullableShape), shapes, additionalProperties);
   }
 
   private static <T> int hashCodeNullable(JsonNullable<T> a) {
@@ -269,7 +266,6 @@ public class Drawing extends HashMap<String, Fruit> {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class Drawing {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    mainShape: ").append(toIndentedString(mainShape)).append("\n");
     sb.append("    shapeOrNull: ").append(toIndentedString(shapeOrNull)).append("\n");
     sb.append("    nullableShape: ").append(toIndentedString(nullableShape)).append("\n");
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java
index 3b0ab1b9322..92848f8415f 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -62,7 +62,7 @@ import org.openapitools.client.ApiClient;
   NullableClass.JSON_PROPERTY_OBJECT_ITEMS_NULLABLE
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class NullableClass extends HashMap<String, Object> {
+public class NullableClass {
   public static final String JSON_PROPERTY_INTEGER_PROP = "integer_prop";
   private JsonNullable<Integer> integerProp = JsonNullable.<Integer>undefined();
 
@@ -603,8 +603,7 @@ public class NullableClass extends HashMap<String, Object> {
         equalsNullable(this.objectNullableProp, nullableClass.objectNullableProp) &&
         equalsNullable(this.objectAndItemsNullableProp, nullableClass.objectAndItemsNullableProp) &&
         Objects.equals(this.objectItemsNullable, nullableClass.objectItemsNullable)&&
-        Objects.equals(this.additionalProperties, nullableClass.additionalProperties) &&
-        super.equals(o);
+        Objects.equals(this.additionalProperties, nullableClass.additionalProperties);
   }
 
   private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
@@ -613,7 +612,7 @@ public class NullableClass extends HashMap<String, Object> {
 
   @Override
   public int hashCode() {
-    return Objects.hash(hashCodeNullable(integerProp), hashCodeNullable(numberProp), hashCodeNullable(booleanProp), hashCodeNullable(stringProp), hashCodeNullable(dateProp), hashCodeNullable(datetimeProp), hashCodeNullable(arrayNullableProp), hashCodeNullable(arrayAndItemsNullableProp), arrayItemsNullable, hashCodeNullable(objectNullableProp), hashCodeNullable(objectAndItemsNullableProp), objectItemsNullable, super.hashCode(), additionalProperties);
+    return Objects.hash(hashCodeNullable(integerProp), hashCodeNullable(numberProp), hashCodeNullable(booleanProp), hashCodeNullable(stringProp), hashCodeNullable(dateProp), hashCodeNullable(datetimeProp), hashCodeNullable(arrayNullableProp), hashCodeNullable(arrayAndItemsNullableProp), arrayItemsNullable, hashCodeNullable(objectNullableProp), hashCodeNullable(objectAndItemsNullableProp), objectItemsNullable, additionalProperties);
   }
 
   private static <T> int hashCodeNullable(JsonNullable<T> a) {
@@ -627,7 +626,6 @@ public class NullableClass extends HashMap<String, Object> {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class NullableClass {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    integerProp: ").append(toIndentedString(integerProp)).append("\n");
     sb.append("    numberProp: ").append(toIndentedString(numberProp)).append("\n");
     sb.append("    booleanProp: ").append(toIndentedString(booleanProp)).append("\n");
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java
index 0f97cb802bb..5b33d0b2b6d 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java
@@ -29,8 +29,6 @@ import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonTypeName;
 import com.fasterxml.jackson.annotation.JsonValue;
 import java.util.Arrays;
-import java.util.HashMap;
-import java.util.Map;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 
 
@@ -42,7 +40,7 @@ import org.openapitools.client.ApiClient;
   TestInlineFreeformAdditionalPropertiesRequest.JSON_PROPERTY_SOME_PROPERTY
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class TestInlineFreeformAdditionalPropertiesRequest extends HashMap<String, Object> {
+public class TestInlineFreeformAdditionalPropertiesRequest {
   public static final String JSON_PROPERTY_SOME_PROPERTY = "someProperty";
   @javax.annotation.Nullable
   private String someProperty;
@@ -130,20 +128,18 @@ public class TestInlineFreeformAdditionalPropertiesRequest extends HashMap<Strin
     }
     TestInlineFreeformAdditionalPropertiesRequest testInlineFreeformAdditionalPropertiesRequest = (TestInlineFreeformAdditionalPropertiesRequest) o;
     return Objects.equals(this.someProperty, testInlineFreeformAdditionalPropertiesRequest.someProperty)&&
-        Objects.equals(this.additionalProperties, testInlineFreeformAdditionalPropertiesRequest.additionalProperties) &&
-        super.equals(o);
+        Objects.equals(this.additionalProperties, testInlineFreeformAdditionalPropertiesRequest.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(someProperty, super.hashCode(), additionalProperties);
+    return Objects.hash(someProperty, additionalProperties);
   }
 
   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class TestInlineFreeformAdditionalPropertiesRequest {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    someProperty: ").append(toIndentedString(someProperty)).append("\n");
     sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
diff --git a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Zebra.java b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Zebra.java
index 68874138ce1..dc09cbb6c96 100644
--- a/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Zebra.java
+++ b/samples/client/petstore/java/native-async/src/main/java/org/openapitools/client/model/Zebra.java
@@ -29,8 +29,6 @@ import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonTypeName;
 import com.fasterxml.jackson.annotation.JsonValue;
 import java.util.Arrays;
-import java.util.HashMap;
-import java.util.Map;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 
 
@@ -43,7 +41,7 @@ import org.openapitools.client.ApiClient;
   Zebra.JSON_PROPERTY_CLASS_NAME
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class Zebra extends HashMap<String, Object> {
+public class Zebra {
   /**
    * Gets or Sets type
    */
@@ -197,20 +195,18 @@ public class Zebra extends HashMap<String, Object> {
     Zebra zebra = (Zebra) o;
     return Objects.equals(this.type, zebra.type) &&
         Objects.equals(this.className, zebra.className)&&
-        Objects.equals(this.additionalProperties, zebra.additionalProperties) &&
-        super.equals(o);
+        Objects.equals(this.additionalProperties, zebra.additionalProperties);
   }
 
   @Override
   public int hashCode() {
-    return Objects.hash(type, className, super.hashCode(), additionalProperties);
+    return Objects.hash(type, className, additionalProperties);
   }
 
   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class Zebra {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    type: ").append(toIndentedString(type)).append("\n");
     sb.append("    className: ").append(toIndentedString(className)).append("\n");
     sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java
index 7fb3620e125..d0777846529 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Drawing.java
@@ -32,9 +32,7 @@ import com.fasterxml.jackson.annotation.JsonTypeName;
 import com.fasterxml.jackson.annotation.JsonValue;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 import org.openapitools.client.model.Fruit;
 import org.openapitools.client.model.NullableShape;
 import org.openapitools.client.model.Shape;
@@ -57,7 +55,7 @@ import org.openapitools.client.ApiClient;
   Drawing.JSON_PROPERTY_SHAPES
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class Drawing extends HashMap<String, Fruit> {
+public class Drawing {
   public static final String JSON_PROPERTY_MAIN_SHAPE = "mainShape";
   @javax.annotation.Nullable
   private Shape mainShape;
@@ -259,7 +257,6 @@ public class Drawing extends HashMap<String, Fruit> {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class Drawing {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    mainShape: ").append(toIndentedString(mainShape)).append("\n");
     sb.append("    shapeOrNull: ").append(toIndentedString(shapeOrNull)).append("\n");
     sb.append("    nullableShape: ").append(toIndentedString(nullableShape)).append("\n");
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java
index fee755d9037..3ff19f9d9cb 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/NullableClass.java
@@ -64,7 +64,7 @@ import org.openapitools.client.ApiClient;
   NullableClass.JSON_PROPERTY_OBJECT_ITEMS_NULLABLE
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class NullableClass extends HashMap<String, Object> {
+public class NullableClass {
   public static final String JSON_PROPERTY_INTEGER_PROP = "integer_prop";
   private JsonNullable<Integer> integerProp = JsonNullable.<Integer>undefined();
 
@@ -609,7 +609,6 @@ public class NullableClass extends HashMap<String, Object> {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class NullableClass {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    integerProp: ").append(toIndentedString(integerProp)).append("\n");
     sb.append("    numberProp: ").append(toIndentedString(numberProp)).append("\n");
     sb.append("    booleanProp: ").append(toIndentedString(booleanProp)).append("\n");
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java
index fd5dcb5d949..a7a1538bc12 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/TestInlineFreeformAdditionalPropertiesRequest.java
@@ -31,8 +31,6 @@ import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonTypeName;
 import com.fasterxml.jackson.annotation.JsonValue;
 import java.util.Arrays;
-import java.util.HashMap;
-import java.util.Map;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 
 
@@ -44,7 +42,7 @@ import org.openapitools.client.ApiClient;
   TestInlineFreeformAdditionalPropertiesRequest.JSON_PROPERTY_SOME_PROPERTY
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class TestInlineFreeformAdditionalPropertiesRequest extends HashMap<String, Object> {
+public class TestInlineFreeformAdditionalPropertiesRequest {
   public static final String JSON_PROPERTY_SOME_PROPERTY = "someProperty";
   @javax.annotation.Nullable
   private String someProperty;
@@ -136,7 +134,6 @@ public class TestInlineFreeformAdditionalPropertiesRequest extends HashMap<Strin
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class TestInlineFreeformAdditionalPropertiesRequest {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    someProperty: ").append(toIndentedString(someProperty)).append("\n");
     sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");
     sb.append("}");
diff --git a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Zebra.java b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Zebra.java
index d9def47f438..7f7968286f3 100644
--- a/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Zebra.java
+++ b/samples/client/petstore/java/native/src/main/java/org/openapitools/client/model/Zebra.java
@@ -31,8 +31,6 @@ import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonTypeName;
 import com.fasterxml.jackson.annotation.JsonValue;
 import java.util.Arrays;
-import java.util.HashMap;
-import java.util.Map;
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 
 
@@ -45,7 +43,7 @@ import org.openapitools.client.ApiClient;
   Zebra.JSON_PROPERTY_CLASS_NAME
 })
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.15.0-SNAPSHOT")
-public class Zebra extends HashMap<String, Object> {
+public class Zebra {
   /**
    * Gets or Sets type
    */
@@ -202,7 +200,6 @@ public class Zebra extends HashMap<String, Object> {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("class Zebra {\n");
-    sb.append("    ").append(toIndentedString(super.toString())).append("\n");
     sb.append("    type: ").append(toIndentedString(type)).append("\n");
     sb.append("    className: ").append(toIndentedString(className)).append("\n");
     sb.append("    additionalProperties: ").append(toIndentedString(additionalProperties)).append("\n");