Gson custom serialization for fields with custom annotation

Question

class Demo {
  private String name;
  private int total;

   ...
}

When I'm serializing an object of demo with gson, I'll get something like this in the normal scenario:

{"name": "hello world", "total": 100}

Now, I have an annotation @Xyz which can be added to any attribute of any class. (The attribute to which I can apply this annotation can be anything, but for now it should be okay if it is just String type )

class Demo {
  @Xyz
  private String name;

  private int total;

  ...
}

When I've the annotation on the class attribute, the serialized data should be of the following format:

{"name": {"value": "hello world", "xyzEnabled": true}, "total": 100}

Please note that this annotation can be applied to any (String) field regardless of the type of the class. If I could somehow get the declared annotations for that specific field on the custom serialiser serialize method, that would work for me.

Please advice how to achieve this.

Answer 1

I think you meant to use annotation JsonAdapter with your custom behaviour

This is a sample class Xyz which extends JsonSerializer, JsonDeserializer

import com.google.gson.*;

import java.lang.reflect.Type;

public class Xyz implements JsonSerializer<String>, JsonDeserializer<String> {

  @Override
  public JsonElement serialize(String element, Type typeOfSrc, JsonSerializationContext context) {
    JsonObject object = new JsonObject();
    object.addProperty("value", element);
    object.addProperty("xyzEnabled", true);
    return object;
  }

  @Override
  public String deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
    return json.getAsString();
  }
}

this is a sample use

import com.google.gson.annotations.JsonAdapter;

public class Demo {
  @JsonAdapter(Xyz.class)
  public String name;
  public int total;
}

I've written some more tests maybe they'll help you to solve this problem more

import com.google.gson.Gson;
import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class Custom {
  @Test
  public void serializeTest() {
    //given
    Demo demo = new Demo();
    demo.total = 100;
    demo.name = "hello world";
    //when
    String json = new Gson().toJson(demo);
    //then
    assertEquals("{\"name\":{\"value\":\"hello world\",\"xyzEnabled\":true},\"total\":100}", json);
  }

  @Test
  public void deserializeTest() {
    //given
    String json = "{  \"name\": \"hello world\",  \"total\": 100}";
    //when
    Demo demo = new Gson().fromJson(json, Demo.class);
    //then
    assertEquals("hello world", demo.name);
    assertEquals(100, demo.total);
  }

}