add example for UserDefinedTemplates (#18423)

samples/client/echo_api/java/okhttp-gson-user-defined-templates/modelCopy/Pet.java

@@ -0,0 +1,151 @@
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.TypeAdapter;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+
+import java.lang.reflect.Type;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import org.openapitools.client.JSON;
+
+/**
+ * Pet
+ */
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", comments = "Generator version: 7.6.0-SNAPSHOT")
+public class Pet {
+  public Pet() {
+  }
+
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash();
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("class Pet {\n");
+    sb.append("}");
+    return sb.toString();
+  }
+
+  /**
+   * Convert the given object to string with each line indented by 4 spaces
+   * (except the first line).
+   */
+  private String toIndentedString(Object o) {
+    if (o == null) {
+      return "null";
+    }
+    return o.toString().replace("\n", "\n    ");
+  }
+
+
+  public static HashSet<String> openapiFields;
+  public static HashSet<String> openapiRequiredFields;
+
+  static {
+    // a set of all properties/fields (JSON key names)
+    openapiFields = new HashSet<String>();
+
+    // a set of required properties/fields (JSON key names)
+    openapiRequiredFields = new HashSet<String>();
+  }
+
+ /**
+  * Validates the JSON Element and throws an exception if issues found
+  *
+  * @param jsonElement JSON Element
+  * @throws IOException if the JSON Element is invalid with respect to Pet
+  */
+  public static void validateJsonElement(JsonElement jsonElement) throws IOException {
+      if (jsonElement == null) {
+        if (!Pet.openapiRequiredFields.isEmpty()) { // has required fields but JSON element is null
+          throw new IllegalArgumentException(String.format("The required field(s) %s in Pet is not found in the empty JSON string", Pet.openapiRequiredFields.toString()));
+        }
+      }
+
+      Set<Map.Entry<String, JsonElement>> entries = jsonElement.getAsJsonObject().entrySet();
+      // check to see if the JSON string contains additional fields
+      for (Map.Entry<String, JsonElement> entry : entries) {
+        if (!Pet.openapiFields.contains(entry.getKey())) {
+          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `Pet` properties. JSON: %s", entry.getKey(), jsonElement.toString()));
+        }
+      }
+  }
+
+  public static class CustomTypeAdapterFactory implements TypeAdapterFactory {
+    @SuppressWarnings("unchecked")
+    @Override
+    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
+       if (!Pet.class.isAssignableFrom(type.getRawType())) {
+         return null; // this class only serializes 'Pet' and its subtypes
+       }
+       final TypeAdapter<JsonElement> elementAdapter = gson.getAdapter(JsonElement.class);
+       final TypeAdapter<Pet> thisAdapter
+                        = gson.getDelegateAdapter(this, TypeToken.get(Pet.class));
+
+       return (TypeAdapter<T>) new TypeAdapter<Pet>() {
+           @Override
+           public void write(JsonWriter out, Pet value) throws IOException {
+             JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             elementAdapter.write(out, obj);
+           }
+
+           @Override
+           public Pet read(JsonReader in) throws IOException {
+             JsonElement jsonElement = elementAdapter.read(in);
+             validateJsonElement(jsonElement);
+             return thisAdapter.fromJsonTree(jsonElement);
+           }
+
+       }.nullSafe();
+    }
+  }
+
+ /**
+  * Create an instance of Pet given an JSON string
+  *
+  * @param jsonString JSON string
+  * @return An instance of Pet
+  * @throws IOException if the JSON string is invalid with respect to Pet
+  */
+  public static Pet fromJson(String jsonString) throws IOException {
+    return JSON.getGson().fromJson(jsonString, Pet.class);
+  }
+
+ /**
+  * Convert an instance of Pet to an JSON string
+  *
+  * @return JSON string
+  */
+  public String toJson() {
+    return JSON.getGson().toJson(this);
+  }
+}