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

I had that error when using guava-gwt with scope "provided". In order to satisfy the dependencies during runtime, I added google-collections. GWT client couldn't deserialize those.

Solution: remove dependency google-collections, and stick with guava.

Answer 2

To problems with serializable objects, you can try this check list:

1. Verify that the class has a default constructor (without arguments)
2. Verify that the class implements Serializable or IsSerializable or implements an Interface that extends Serializable or extends a class that implement Serializable
3. Verify that the class is in a client.* package or …
4. Verify, if the class is not in client.* package, that is compiled in your GWT xml module definition. By default is present. If your class is in another package you have to add it to source. For example if your class is under domain.* you should add it to xml as . Be aware that the class cannot belong to server package! More details on GWT page: http://code.google.com/webtoolkit/doc/latest/DevGuideOrganizingProjects.html#DevGuideModuleXml
5. If you are including the class from another GWT project you have to add the inherits to your xml module definition. For example if your class Foo is in the package com.dummy.domain you have to add to the module definition. More details here: http://code.google.com/webtoolkit/doc/latest/DevGuideOrganizingProjects.html#DevGuideInheritingModules
6. If you are including the class from another GWT project released as a jar verify that the jar contains also the source code because GWT recompile also the Java source for the classes passed to the Client.

Font: http://isolasoftware.it/2011/03/22/gwt-serialization-policy-error/

Answer 3

I am working in a team with mature software which one day stopped working for me due to this error. The rest of the team was fine. We tried any number of things to fix it. Eventually, we reinstalled IntelliJ and that fixed it.

Answer 4

I would try a couple of things.

• In User implement just com.google.gwt.user.client.rpc.IsSerializable and add a blank constructor. I remember reading somewhere a long time ago that this is needed and it solved a problem like this in one of my projects. public User() { }
• Make sure your package is defined in your gwt.xml file.

You are not doing anything more complicated that cannot be serialized so you should be fine with that.

Answer 5

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.

Answer 6

Sometimes this error can be due to outdated/corrupted client-side files/cache (There is no server side error message in this case). I just ran "rebuild module" in IntelliJ and it was fine again.