GWT: The response could not be deserialized

Question

I'm using GWT (2.4) with Spring integrated as in this article. I have problem with getting list of User from database (Hibernate) and populate DataGrid with it. When i call greetingService.allUsers() method, I'm getting error (onFailure()):

com.google.gwt.user.client.rpc.IncompatibleRemoteServiceException: The response could not be deserialized

Anybody helps with that? Below some pieces of code. Full working project is here.

  public void onModuleLoad() {
    // ...
    greetingService.allUsers(
        new AsyncCallback<List<User>>(){
            @Override
            public void onFailure(Throwable caught) {
                caught.printStackTrace();
            }
            @Override
            public void onSuccess(List<User> result) {
                GWT.log("SIZE: "+result.size());
                dataGrid.setRowData(result);
            }
        }
    );
    // ...
 }

GreetingServiceImpl

@Override
public List<User> allUsers() {
    return userDAO.findAll();
}

User

@Entity
@Table(name = "users")
public class User implements Serializable, IsSerializable {

    @Id
    private Long id;

    // only Strings and one Date
    private String login;
    private String password;
    private String firstname;
    private String lastname;
    private Date date;
}

Answer 1

Documentation for IncompatibleRemoteServiceException says:

This exception can be caused by the following problems:

• The requested {@link RemoteService} cannot be located via {@link Class#forName(String)} on the server.
• The requested {@link RemoteService} interface is not implemented by the {@link com.google.gwt.user.server.rpc.RemoteServiceServlet RemoteServiceServlet} instance which is configured to process the request.
• The requested service method is not defined or inherited by the requested {@link RemoteService} interface.


• One of the types used in the {@link RemoteService} method invocation has had fields added or removed.
• The client code receives a type from the server which it cannot
  deserialize.

In your case is the last point, you have a type which cannot be serialized and deserialized, that's a your User class is one of them. You should have one transfer object which implements com.google.gwt.user.client.rpc.IsSerializable interface for transmitting the User object across the network. For further information see: Compatibility with the Java Language and Libraries. GWT RPC method parameters and return types must be transmitted across a network between client and server applications and therefore they must be serializable.