ListWriter.java

package svanimpe.reminders.json;

import java.io.IOException;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.json.Json;
import javax.json.JsonObjectBuilder;
import javax.json.JsonWriter;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
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.MessageBodyWriter;
import javax.ws.rs.ext.Provider;
import svanimpe.reminders.domain.List;

@Provider
@Produces(MediaType.APPLICATION_JSON)
public class ListWriter implements MessageBodyWriter<List>
{
    @Override
    public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType)
    {
        return List.class.isAssignableFrom(type);
    }

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

    @Override
    public void writeTo(List list, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException
    {    
        JsonObjectBuilder jsonList = Json.createObjectBuilder();
        jsonList.add("id", list.getId());
        jsonList.add("owner", list.getOwner().getUsername());
        jsonList.add("title", list.getTitle());
        
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("RemindersPU");
        EntityManager em = emf.createEntityManager();
        Query q = em.createNamedQuery("List.findSize").setParameter("list", list);
        jsonList.add("size", (Long) q.getSingleResult());
        em.close();
        emf.close();

        try (JsonWriter writer = Json.createWriter(entityStream)) {
            writer.writeObject(jsonList.build());
        }
    }
}