spring jersey POST serialized bean

Question

Is there any way to get POST request body as serialized bean instead of raw json string ? for example:

    @POST
    @Path(ResourceEndpoints.POST_USER_REGISTER)
    @Produces(MediaType.APPLICATION_JSON)
    public Response register(@RequestBody UserObject user) {
    ...

Then I would not have to write json serializer boiler-plate code in each request.

Currently I have to do like this:

    @POST
    @Path(ResourceEndpoints.POST_USER_REGISTER)
    @Produces(MediaType.APPLICATION_JSON)
    public Response register(@RequestBody String userObjectJson) {
        Gson gson = new Gson();
        UserObject userObject = gson.fromJson(userObjectJson, UserObject.class);

Answer 1

If you must stick to Gson, you need to write a MessageBodyReader / MessageBodyWriter pair to handle deserialization/serialization. This is how the request stream is converted into our domain objects and domain objects serialized to the response stream.

You can find a good explanation about this subject here and you can find a simple implementation here at Integrating Gson into a JAX-RS based application . I will post the implementation at the bottom (in case the side ever goes down).

However you register all your other Jersey components, ie resource classes and providers, register this GsonMessageBodyHandler the same way. If you have package scanning enabled, the class should be automatically picked up from the @Provider annotation. In any case the @RequestBody annotation shouldn't be needed (I don't work much with Spring, but I would guess it's ignored either way).

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

import javax.ws.rs.Consumes;
import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

@Provider
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public final class GsonMessageBodyHandler implements MessageBodyWriter<Object>,
    MessageBodyReader<Object> {

  private static final String UTF_8 = "UTF-8";

  private Gson gson;

  private Gson getGson() {
    if (gson == null) {
      final GsonBuilder gsonBuilder = new GsonBuilder();
      gson = gsonBuilder.create();
    }
    return gson;
  }

  @Override
  public boolean isReadable(Class<?> type, Type genericType,
      java.lang.annotation.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 Exception, ApplicationException {
    InputStreamReader streamReader = new InputStreamReader(entityStream, UTF_8);
    try {
      Type jsonType;
      if (type.equals(genericType)) {
        jsonType = type;
      } else {
        jsonType = genericType;
      }
      return getGson().fromJson(streamReader, jsonType);
    } finally {
      streamReader.close();
    }
  }

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

  @Override
  public long getSize(Object object, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
    return -1;
  }

  @Override
  public void writeTo(Object object, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException {
    OutputStreamWriter writer = new OutputStreamWriter(entityStream, UTF_8);
    try {
      Type jsonType;
      if (type.equals(genericType)) {
        jsonType = type;
      } else {
        jsonType = genericType;
      }
      getGson().toJson(object, jsonType, writer);
    } finally {
      writer.close();
    }
  }
}