GsonMessageBodyHandler.java

package com.breeze.jersey;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
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.breeze.util.JsonGson;
import com.google.gson.Gson;

/**
 * Plugs in to Jersey to allow it to use GSON for JSON serialization.
 * Not actually needed because Breeze does JSON serialization directly using GSON.
 * 
 * @see http://eclipsesource.com/blogs/2012/11/02/integrating-gson-into-a-jax-rs-based-application/ 
 */
@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 getGson(boolean toJson) {
        Gson gson;
        if (toJson) {
            gson = JsonGson.newGsonBuilder(true, true).create();
        } else {
            gson = JsonGson.newGsonBuilder(false, false).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) {
        InputStreamReader streamReader = null;
        try {
            streamReader = new InputStreamReader(entityStream, UTF_8);
            Type jsonType;
            if (type.equals(genericType)) {
                jsonType = type;
            } else {
                jsonType = genericType;
            }
            return getGson(false).fromJson(streamReader, jsonType);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException("UTF-8 not supported?!");
        } finally {
            if (streamReader != null) try {
                streamReader.close();
            } catch (IOException e) {
                // ignore
            }
        }
    }

    @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(true).toJson(object, jsonType, writer);
        } finally {
            writer.close();
        }
    }
}