Question

HTTP controller (Spring) gets a requests and making a blocking call. Once the blocking call is over the controls get back to the controller.

At this point I don’t want to send a response back to the client but rather wait for another event(e.g., completion of some processing) to happen. As soon as that event happens I need a way to collect the data from the event and then return the HTTP response with this data.

HTTPController doSomething( HTTPRequest ) 
{
    makeBlockingCall();  
    waitForEventToHappen();
    collectDataFromEvent();

    return HTTPResponse(); 

}

Answer 1

You wouldn’t do that from within one request, because that would probably time out eventually and until then wouldn’t provide feedback to the customer that something is happening.

Instead, you would immediately show a page that asynchronously (probably per AJAX) polls the server to see whether the result is already available.

So the first request will return an id that will be used in the second (AJAX) request to lookup the result.