public class MainRpcServiceImpl extends RemoteServiceServlet implements MainRpcService {

    @Inject
    EntityManager em;

    private List weatherList = new ArrayList<>();

    public MainRpcServiceImpl(){
        EntityManagerFactory managerFactory = Persistence.createEntityManagerFactory("jpaPersistenceUnit");
        em = managerFactory.createEntityManager();

    }

    @Override
    public List<WeatherEntity> getAllWeatherEntity() {
        Query query = em.createQuery("from WeatherEntity");
        weatherList = query.getResultList();
        return weatherList;
    }

    @Override
    public WeatherEntity saveWeatherEntity (WeatherEntity weatherEntity) {

        weatherEntity.setCity("NewYork");
        weatherEntity.setPrcp(1111);
        weatherEntity.setTempLo(222);
        weatherEntity.setTempHi(333);
        weatherEntity.setDate("11/11/2011");

        em.merge(weatherEntity);
        return null;
    }
}

@RemoteServiceRelativePath("gwtPersistenceService")
public interface MainRpcService extends RemoteService {
    List<WeatherEntity> getAllWeatherEntity();
    WeatherEntity saveWeatherEntity (WeatherEntity weatherEntity);
}

public interface MainRpcServiceAsync {
    void getAllWeatherEntity(AsyncCallback<List<WeatherEntity>> async);
    void saveWeatherEntity(WeatherEntity weatherEntity, AsyncCallback<WeatherEntity> async);
}

public class Main implements EntryPoint {
    public void onModuleLoad() {

        /*init rpc service */
        final MainRpcServiceAsync rpcService = GWT.create(MainRpcService.class);

                 /* Save -------------------------------------------------------------- */
                 rpcService.saveWeatherEntity(new WeatherEntity(), new AsyncCallback<WeatherEntity>() {
                     @Override
                     public void onFailure(Throwable caught) {
                         Window.alert("Failure: " + caught.getMessage());
                     }

                     @Override
                     public void onSuccess(WeatherEntity result) {
                         Window.alert("Успех!");

//Тут что-т о надо передать??? result.setCity("NewYork"); - не канает.

                     }
                 });

}

public class appMain {

    public static void main(String[] args) {
        appMethods app = new appMethods();
        app.AddWeather("Троицк", 1234, 2345, 2346, "01.01.2013");
        app.AddWeather("Верхневинск", 1234, 2345, 2146, "02.01.2013");
        app.AddWeather("Калуга", 1234, 2345, 2346, "03.01.2013");
    }
}

public class appMethods {

    public void AddWeather(String city, Integer prcp, Integer temphi, Integer templo, String date) {

        Session session = HibernateSessionFactory.getSessionFactory().openSession();
        session.beginTransaction();
        WeatherEntity weatherEntity = new WeatherEntity();

        weatherEntity.setCity(city);
        weatherEntity.setPrcp(prcp);
        weatherEntity.setTempHi(temphi);
        weatherEntity.setTempLo(templo);
        weatherEntity.setDate(date);

        session.save(weatherEntity);
        session.getTransaction().commit();
        session.close();

    }

    public void DeleteWeather(String city){
        Session session = HibernateSessionFactory.getSessionFactory().openSession();
        session.beginTransaction();
        WeatherEntity weatherEntity = new WeatherEntity();

        List list = session.createQuery("from WeatherEntity where city='" + city + "'").list();
        Iterator itr = list.iterator();

        while(itr.hasNext()){
            WeatherEntity we = (WeatherEntity)itr.next();
            session.delete(we);
        }
        session.getTransaction().commit();
        session.save(weatherEntity);
    }

}

public class HibernateSessionFactory {

    private static SessionFactory sessionFactory = buildSessionFactory();
    protected static SessionFactory buildSessionFactory() {

        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure() // configures settings from hibernate.cfg.xml
                .build();
        try {
            sessionFactory = new MetadataSources( registry ).buildMetadata().buildSessionFactory();
        }
        catch (Exception e) {
            StandardServiceRegistryBuilder.destroy( registry );
            throw new ExceptionInInitializerError("Initial SessionFactory failed" + e);
        }
        return sessionFactory;
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
    public static void shutdown() {
        // Close caches and connection pools
        getSessionFactory().close();
    }

}