How to intercept the onSuccess() method in GWT - gwt

Question

I need to do method interception for the onSuccess method in GWT.
I need to add some code before and after the calling of the onSuccess method in GWT? (I have many calls to the onSuccess method and I need to do this dynamically)
EDIT:
I need to add a progress bar in the right corner of the screen, that appears when the code enters the onsuccess method and disappears on the exit of onsuccess method.

Answer 1

From a visual perspective
void onSuccess(Value v) {
showProgressBar();
doLotsOfWork(v);
hideProgressBar();
}
will be a no-op. Browsers typically wait for event handlers to finish executing before re-rending the DOM. If the doLotsOfWork() method takes a noticeable amount of time to execute (e.g. >100ms) the user will notice the browser hiccup due to the single-threaded nature of JavaScript execution.
Instead, consider using an incrementally-scheduled command to break the work up. It would look roughly like:
void onSuccess(Value v) {
showProgressBar();
Scheduler.get().scheduleIncremental(new RepeatingCommand() {
int count = 0;
int size = v.getElements().size();
public boolean execute() {
if (count == size) {
hideProgressBar();
return false;
}
processOneElement(v.getElements().get(count++));
setProgressBar((double) count / size);
return true;
}
});
}
By breaking the work across multiple pumps of the browser's event loop, you avoid the situation where the webapp becomes non-responsive if there's a non-trivial amount of work to do.

Answer 2

Well, it is a generic non-functional requirement, I have done some research on this item, I have implemented a solution that Thomas Broyer has suggested on gwt group.. This solution has distinct advantage over other suggested solutions, You dont have to change your callback classes, what you have to do is just add a line of code after creation of async gwt-rpc service...
IGwtPersistenceEngineRPCAsync persistenceEngine = GWT.create(IGwtPersistenceEngineRPC.class);
((ServiceDefTarget) persistenceEngine).setRpcRequestBuilder(new ProgressRequestBuilder());
import com.allen_sauer.gwt.log.client.Log;
import com.google.gwt.http.client.Request;
import com.google.gwt.http.client.RequestBuilder;
import com.google.gwt.http.client.RequestCallback;
import com.google.gwt.http.client.Response;
import com.google.gwt.user.client.rpc.RpcRequestBuilder;
public class ProgressRequestBuilder extends RpcRequestBuilder {
private class RequestCallbackWrapper implements RequestCallback {
private RequestCallback callback;
RequestCallbackWrapper(RequestCallback aCallback) {
this.callback = aCallback;
}
#Override
public void onResponseReceived(Request request, Response response) {
Log.debug("onResposenReceived is called");
// put the code to hide your progress bar
callback.onResponseReceived(request, response);
}
#Override
public void onError(Request request, Throwable exception) {
Log.error("onError is called",new Exception(exception));
// put the code to hide your progress bar
callback.onError(request, exception);
}
}
#Override
protected RequestBuilder doCreate(String serviceEntryPoint) {
RequestBuilder rb = super.doCreate(serviceEntryPoint);
// put the code to show your progress bar
return rb;
}
#Override
protected void doFinish(RequestBuilder rb) {
super.doFinish(rb);
rb.setCallback(new RequestCallbackWrapper(rb.getCallback()));
}
}

Answer 3

You cant do that. The rpc onSuccess() method runs asynchronously (in other words, depends on the server when it completes, the app doesnt wait for it). You could fire code immediately after the rpc call which may/ may not complete before the onSuccess for RPC calls.
Can you explain with an eg why exactly do u want to do that? Chances are you might have to redesign the app due to this async behavior, but cant say till you provide a use case. Preferably any Async functionality should be forgotten after the rpc call, and actioned upon only in the onSuccess.