When session timeout redirect to login page in GWT project

Could you advice me how to proceed in catching session timeout in a GWT project. I m using gwt dispatch lib. I m wonderig can i do something like implementing a开发者_如何转开发 filter and then checking if session exist or no but i suppose in gwt projects there are different approaches. Any help is welcome.

Thanks

Client: All Callbacks extend a Abstract Callback where you implement the onFailur()

public abstract class AbstrCallback<T> implements AsyncCallback<T> {

  @Override
  public void onFailure(Throwable caught) {
    //SessionData Expired Redirect
    if (caught.getMessage().equals("500 " + YourConfig.ERROR_MESSAGE_NOT_LOGGED_IN)) {
      Window.Location.assign(ConfigStatic.LOGIN_PAGE);
    }
    // else{}: Other Error, if you want you could log it on the client
  }
}

Server: All your ServiceImplementations extend AbstractServicesImpl where you have access to your SessionData. Override onBeforeRequestDeserialized(String serializedRequest) and check the SessionData there. If the SessionData has expire then write a spacific error message to the client. This error message is getting checkt in your AbstrCallback and redirect to the Login Page.

public abstract class AbstractServicesImpl extends RemoteServiceServlet {

  protected ServerSessionData sessionData;

  @Override
  protected void onBeforeRequestDeserialized(String serializedRequest) {

    sessionData = getYourSessionDataHere()

    if (this.sessionData == null){ 
      // Write error to the client, just copy paste
      this.getThreadLocalResponse().reset();
      ServletContext servletContext = this.getServletContext();
      HttpServletResponse response = this.getThreadLocalResponse();
      try {
        response.setContentType("text/plain");
        response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        try {
          response.getOutputStream().write(
            ConfigStatic.ERROR_MESSAGE_NOT_LOGGED_IN.getBytes("UTF-8"));
          response.flushBuffer();
        } catch (IllegalStateException e) {
          // Handle the (unexpected) case where getWriter() was previously used
          response.getWriter().write(YourConfig.ERROR_MESSAGE_NOT_LOGGED_IN);
          response.flushBuffer();
        }
      } catch (IOException ex) {
        servletContext.log(
          "respondWithUnexpectedFailure failed while sending the previous failure to the client",
          ex);
      }
      //Throw Exception to stop the execution of the Servlet
      throw new NullPointerException();
    }
  }

}

In Addition you can also Override doUnexpectedFailure(Throwable t) to avoid logging the thrown NullPointerException.

@Override
protected void doUnexpectedFailure(Throwable t) {
  if (this.sessionData != null) {
    super.doUnexpectedFailure(t);
  }
}