GsonJSONProvider.java

package net.olemartin.tools;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import net.olemartin.domain.*;

import javax.ws.rs.Consumes;
import javax.ws.rs.Produces;
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 java.io.*;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

@Provider
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public final class GsonJSONProvider 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();
            gsonBuilder.registerTypeAdapter(Tournament.class, new Tournament.TournamentSerializer());
            gsonBuilder.registerTypeAdapter(Round.class, new Round.RoundSerializer());
            gsonBuilder.registerTypeAdapter(Player.class, new Player.PlayerSerializer());
            gsonBuilder.registerTypeAdapter(Person.class, new Person.PersonSerializer());
            gsonBuilder.registerTypeAdapter(User.class, new User.UserSerializer());
            gsonBuilder.registerTypeAdapter(Match.class, new Match.MatchSerializer());
            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 IOException {

        try (InputStreamReader streamReader = new InputStreamReader(entityStream, UTF_8)) {
            Type jsonType;
            if (type.equals(genericType)) {
                jsonType = type;
            } else {
                jsonType = genericType;
            }
            return getGson().fromJson(streamReader, jsonType);
        }
    }

    @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 {

        try (OutputStreamWriter writer = new OutputStreamWriter(entityStream, UTF_8)) {
            Type jsonType;
            if (type.equals(genericType)) {
                jsonType = type;
            } else {
                jsonType = genericType;
            }
            getGson().toJson(object, jsonType, writer);
        }
    }
}