GWT RPC possible in window closing handler? - gwt

Question

I'm listening for a window close event:
closeHandlerReg = Window.addCloseHandler(new CloseHandler<Window>() {
#Override
public void onClose(CloseEvent<Window> event) {
// ...
}
});
The documentation says that no UI can be shown in that callback. What about GWT RPC calls? I'm trying to make one, but it isn't showing up on the server (either in breakpoints or log statements).

Answer 1

Problem is that GWT RPC is asynchronous and the calls to RPC services return immediately. In this case the window is closed before the browser has a chance to send the underlying XMLHTTPRequest.
If it's absolutely necessary you should be able to hand-craft calling some sort of servlet (not GWT RPC) with a "synchronous" XMLHTTPRequest. Have a look here for an example: http://weblogs.asp.net/bleroy/archive/2005/12/15/433278.aspx
But really you shouldn't be doing anything of this sort in the window.onunload or window.onbeforeunload (these are the underlying DOM events for CloseEvent and ClosingEvent for the Window. Perhaps there is a better way to do what you are trying to do.

Answer 2

The use case you have should be possible. When you make the RPC call in the closeHandler it should arrive at the server, because while it returns directly, it has started sending the data, and set a callback to wait for the result. However the callback will fail because the connection is lost because the window is closed. But that is no problem as you only want to notify the server. So the question might be what are you sending? and does it work at all, when you send it at some other point in the code, not in the closeHandler?

Answer 3

Old question, but still - maybe someone faces the same issue.
RPCs won't work in the closing handler as already discussed. This workaround worked for me:
In the onClose method, do something like:
Window.Location.replace(GWT.getModuleBaseURL() + "rpcCall?param1=" + param1 + "&param2=" + param2);
whereas "rpcCall" is the name of the rpc url you have set in your web.xml file. Of course, a random number of parameters may be passed within the URL.
Then, in your server-side implementation of your rpc interface, you can override the doGet method:
#Override
public void doGet(HttpServletRequest request, HttpServletResponse response) {
String param1 = URLDecoder.decode(request.getParameter("param1"), "UTF-8");
String param2 = URLDecoder.decode(request.getParameter("param2"), "UTF-8");
// do something
}

Answer 4

And another solution: Don't do an rpc call on window closing, but a regular http call that can then be handled by a custom servlet on the server side.
In your GWT module, do something like this:
Window.addWindowClosingHandler(new ClosingHandler() {
#Override
public void onWindowClosing(ClosingEvent event) {
sendWindowClosed(GWT.getModuleBaseURL() + "teardownservice");
}
});
private native void sendWindowClosed(String url)
/*-{
var Http = new XMLHttpRequest();
Http.open("GET", url);
Http.send();
}-*/;
}
In the server-side servlet, you can then handle this call:
public class TearDownServlet extends HttpServlet {
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
.... whatever you want ....
}
}