gson Using Gson with JAX-RS (RESTful web services) JAX-RS provider to use Gson

Example

This is a custom JAX-RS @Provider to use Gson as the JSON parser. The example also shows how to use custom Java 8 date/time converters.

@Provider
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public class JerseyServerGson  
        implements MessageBodyWriter<Object>, MessageBodyReader<Object>
{
  @Override
  public boolean isReadable(Class<?> type,
                            Type genericType,
                            Annotation[] annotations,
                            MediaType mediaType)
  {
    return true;
  }

  @Override
  public Object readFrom(Class<Object> type,
                         Type genericType,
                         Annotation[] annotations,
                         MediaType mediaType,
                         MultivaluedMap<String, String> httpHeaders,
                         InputStream entityStream)
          throws IOException, WebApplicationException
  {
    try ( InputStreamReader input = 
                  new InputStreamReader(entityStream, "UTF-8") ) {
      Gson gson = getGson();
      return gson.fromJson(input, genericType);
    }
  }

  @NotNull
  private Gson getGson() {
    return new GsonBuilder()
            .registerTypeAdapter(LocalDateTime.class,
                                 new AdapterLocalDateTime().nullSafe())
            .registerTypeAdapter(LocalDate.class,
                                 new AdapterLocalDate().nullSafe())
            .setPrettyPrinting()
            .serializeNulls()
            .create();
  }

  @Override
  public boolean isWriteable(Class<?> type,
                             Type genericType,
                             Annotation[] annotations,
                             MediaType mediaType)
  {
    return true;
  }

  @Override
  public long getSize(Object o,
                      Class<?> type,
                      Type genericType,
                      Annotation[] annotations,
                      MediaType mediaType)
  {
    // Deprecated and ignored in Jersey 2
    return -1;
  }

  @Override
  public void writeTo(Object o,
                      Class<?> type,
                      Type genericType,
                      Annotation[] annotations,
                      MediaType mediaType,
                      MultivaluedMap<String, Object> httpHeaders,
                      OutputStream entityStream)
          throws IOException, WebApplicationException
  {
    try ( OutputStreamWriter writer = 
                  new OutputStreamWriter(entityStream, "UTF-8") ) {
      getGson().toJson(o, genericType, writer);
    }
  }
}