Gson: How to change output of Enum

Question

I've this enum:

enum RequestStatus {
  OK(200), NOT_FOUND(400);

  private final int code;

  RequestStatus(int code) {
    this.code = code;
  }

  public int getCode() {
    return this.code;
  }
};

and in my Request-class, I have this field: private RequestStatus status.

When using Gson to convert the Java object to JSON the result is like:

"status": "OK"

How can I change my GsonBuilder or my Enum object to give me an output like:

"status": {
  "value" : "OK",
  "code" : 200
}

Answer 1

You can use something like this:

GsonBuilder builder = new GsonBuilder(); builder.registerTypeAdapterFactory(new MyEnumAdapterFactory()); 

or more simply (as Jesse Wilson indicated):

GsonBuilder builder = new GsonBuilder(); builder.registerTypeAdapter(RequestStatus.class, new MyEnumTypeAdapter()); 

and

public class MyEnumAdapterFactory implements TypeAdapterFactory {      @Override     public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> type) {             Class<? super T> rawType = type.getRawType();             if (rawType == RequestStatus.class) {                 return new MyEnumTypeAdapter<T>();             }             return null;     }      public class MyEnumTypeAdapter<T> extends TypeAdapter<T> {           public void write(JsonWriter out, T value) throws IOException {               if (value == null) {                    out.nullValue();                    return;               }               RequestStatus status = (RequestStatus) value;               // Here write what you want to the JsonWriter.                out.beginObject();               out.name("value");               out.value(status.name());               out.name("code");               out.value(status.getCode());               out.endObject();          }           public T read(JsonReader in) throws IOException {               // Properly deserialize the input (if you use deserialization)               return null;          }     }  } 

Answer 2

In addition to Polet's answer, if you need a generic Enum serializer, you can achieve it via reflection:

public class EnumAdapterFactory implements TypeAdapterFactory
{

    @Override
    public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> type)
    {
        Class<? super T> rawType = type.getRawType();
        if (rawType.isEnum())
        {
            return new EnumTypeAdapter<T>();
        }
        return null;
    }

    public class EnumTypeAdapter<T> extends TypeAdapter<T>
    {
        @Override
        public void write(JsonWriter out, T value) throws IOException
        {
            if (value == null || !value.getClass().isEnum())
            {
                out.nullValue();
                return;
            }

            try
            {
                out.beginObject();
                out.name("value");
                out.value(value.toString());
                Arrays.stream(Introspector.getBeanInfo(value.getClass()).getPropertyDescriptors())
                      .filter(pd -> pd.getReadMethod() != null && !"class".equals(pd.getName()) && !"declaringClass".equals(pd.getName()))
                      .forEach(pd -> {
                          try
                          {
                              out.name(pd.getName());
                              out.value(String.valueOf(pd.getReadMethod().invoke(value)));
                          } catch (IllegalAccessException | InvocationTargetException | IOException e)
                          {
                              e.printStackTrace();
                          }
                      });
                out.endObject();
            } catch (IntrospectionException e)
            {
                e.printStackTrace();
            }
        }

        public T read(JsonReader in) throws IOException
        {
            // Properly deserialize the input (if you use deserialization)
            return null;
        }
    }
}

Usage:

@Test
public void testEnumGsonSerialization()
{
    List<ReportTypes> testEnums = Arrays.asList(YourEnum.VALUE1, YourEnum.VALUE2);
    GsonBuilder builder = new GsonBuilder();
    builder.registerTypeAdapterFactory(new EnumAdapterFactory());
    Gson gson = builder.create();
    System.out.println(gson.toJson(reportTypes));
}