How to trigger onFailure in GWT RPC? [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

StatusCodeException Vs. RuntimeException in GWT

I want to trigger RPC callback "onFailure" if the session expires in the server. I created a custom RPC AsyncCallback that handles the "session expired" event from the server. I overrode RemoteServiceServlet to validate the session prior to invoking the method. So basically, it is not the declared method that throws the exception but the custom RemoteServiceServlet. It still goes to the "onFailure" in the client async but the Throwable object is still of type "StatusCodeException" without the EXPIRED_SESSION_MSG message. Any ideas?

Custom RemoteServiceServlet:

public class XRemoteServiceServlet extends RemoteServiceServlet {
    private final static String EXPIRED_SESSION_MSG = "ERROR: Application has expired session.";   
    @Override
    protected void onAfterRequestDeserialized(RPCRequest rpcRequest) {
        HttpServletRequest httpServletRequest = this.getThreadLocalRequest();
        HttpSession session = httpServletRequest.getSession(false);
        if (session != null) {
            final String sessionIdFromRequestHeader = getSessionIdFromHeader();
            if (!isNullOrEmptyString(sessionIdFromRequestHeader)) {
                final String sessionId = session.getId();

                if (!sessionId.equals(sessionIdFromRequestHeader)) {
                    throw new RuntimeException(EXPIRED_SESSION_MSG);
                }
            }

Custom AsyncCallback:

public class XAsyncCallback<T> implements AsyncCallback<T> {
    private final static String EXPIRED_SESSION_MSG = "ERROR: Application has expired session.";

    @Override
    public void onFailure(Throwable caught) {
        final String message = caught.getMessage();

        if (!isNullOrEmptyString(message) && message.contains(EXPIRED_SESSION_MSG)) {
            com.google.gwt.user.client.Window.Location.relo开发者_运维百科ad();
        }

    }

    @Override
    public void onSuccess(T arg0) {

    }

    /**
     * Returns true if the string is null or equals to the empty string.
     * 
     * @param string the string to test
     * @return true if the string is empty
     */
    private static boolean isNullOrEmptyString(String string) {
        return string == null || "".equals(string);
    }
}

---

See here for handling exceptions with GWT RPC.

An "expected failure" is an exception thrown by a service method that is declared in the signature of the service method. These exceptions are serialized back to the client.

"Unexpected expections" are errors that are not part of the service method's signature, or that result from SecurityExceptions, SerializationExceptions, or other failures within the RPC framework.

What you want is a checked exception, because you want to send it back to the client and do something about it. The RPC framework is in charge of catching it, serializing it and calling the onFailure method with the right exception. In order to do that, you need to follow its guidelines which are :

• You need to specifiy in the service signature that the exception can be thrown.
• The exception must be thrown in the service implementation method.

What you're doing is throwing an unexcepted exception from some method that shouldn't even be throwing exceptions. So RPC doesn't know what really happened and sends back a generic message saying 'Hey, something unexpected happened, look at the server log'.

I understand that you want to check the session on every call. Your easiest option is to have a method to check that in your servlet implementation and call it from all your service methods.

Otherwise, you can try to override the GWT RPC framework by looking at the class

com.google.gwt.user.server.rpc.RPC

but that's pretty advanced stuff.

---

If you want to send exceptions via GWT-RPC you must use checked exceptions. RuntimeException is an unchecked exception so you can not use it in this case.

Create your own exception that extends Exception and implements Serializable. Also, you must indicate on methods declaration that this method might throw an exceptions: