GsonObjectMessageBodyHandler.java

package io.fathom.cloud.server;

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.inject.Singleton;
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;
import com.google.gson.JsonElement;
import com.google.gson.JsonParser;

@Provider
@Singleton
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public final class GsonObjectMessageBodyHandler implements MessageBodyWriter<Object>, MessageBodyReader<Object> {
    private static final String UTF_8 = "UTF-8";

    private Gson gson;

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

    @Override
    public boolean isReadable(Class<?> type, Type genericType, java.lang.annotation.Annotation[] annotations,
            MediaType mediaType) {
        if (JsonElement.class.isAssignableFrom(type)) {
            return true;
        }
        return false;
    }

    @Override
    public Object readFrom(Class<Object> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders, InputStream entityStream) throws IOException {
        InputStreamReader streamReader = new InputStreamReader(entityStream, UTF_8);
        try {
            Type jsonType;
            if (type.equals(genericType)) {
                jsonType = type;
            } else {
                jsonType = genericType;
            }
            if (JsonElement.class.isAssignableFrom(type)) {
                JsonParser parser = new JsonParser();
                JsonElement jsonElement = parser.parse(streamReader);
                return jsonElement;
            } else {
                throw new IllegalArgumentException();

                // Gson gson = getGson();
                // return gson.fromJson(streamReader, jsonType);
            }
        } finally {
            streamReader.close();
        }
    }

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

    @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;
            }

            Gson gson = getGson();
            if (JsonElement.class.isAssignableFrom(type)) {
                gson.toJson((JsonElement) object, writer);
            } else {
                throw new IllegalArgumentException();
                // gson.toJson(object, jsonType, writer);
            }
        } finally {
            writer.close();
        }
    }
}