Interface JsonSerializer<T>

  • Type Parameters:
    T - type for which the serializer is being registered. It is possible that a serializer may be asked to serialize a specific generic type of the T.

    public interface JsonSerializer<T>
    Interface representing a custom serializer for Json. You should write a custom serializer, if you are not happy with the default serialization done by Gson. You will also need to register this serializer through GsonBuilder.registerTypeAdapter(Type, Object).

    Let us look at example where defining a serializer will be useful. The Id class defined below has two fields: clazz and value.

     public class Id<T> {
       private final Class<T> clazz;
       private final long value;
       public Id(Class<T> clazz, long value) {
         this.clazz = clazz;
         this.value = value;
       public long getValue() {
         return value;

    The default serialization of Id(, 20L) will be {"clazz","value":20}. Suppose, you just want the output to be the value instead, which is 20 in this case. You can achieve that by writing a custom serializer:

     class IdSerializer implements JsonSerializer<Id>() {
       public JsonElement serialize(Id id, Type typeOfId, JsonSerializationContext context) {
         return new JsonPrimitive(id.getValue());

    You will also need to register IdSerializer with Gson as follows:

     Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdSerializer()).create();

    New applications should prefer TypeAdapter, whose streaming API is more efficient than this interface's tree API.

    • Method Detail

      • serialize

        JsonElement serialize​(T src,
                              java.lang.reflect.Type typeOfSrc,
                              JsonSerializationContext context)
        Gson invokes this call-back method during serialization when it encounters a field of the specified type.

        In the implementation of this call-back method, you should consider invoking JsonSerializationContext.serialize(Object, Type) method to create JsonElements for any non-trivial field of the src object. However, you should never invoke it on the src object itself since that will cause an infinite loop (Gson will call your call-back method again).

        src - the object that needs to be converted to Json.
        typeOfSrc - the actual type (fully genericized version) of the source object.
        a JsonElement corresponding to the specified object.