Thread: Servlet request time out error

So effectively you've got an asynchronous process but you're trying to treat it as a synchronous process.

My recommendation would be two fold. First, no user wants to wait 4 minutes for a result in a web environment. You're going to have users reloading and/or giving up and sending in bug reports. So, at the very least, send the request off from the browser to start the process and then, via JavaScript, poll the back end to see if the process is done. You only have to poll like every 10 seconds or so which isn't very expensive. Of course, that depends on many factors but without support of something like WebSockets a poll is the safest way.

The second recommedation which is closely related to the first is to have process1() be able to post some sort of progress. Even if it's just an estimate your front end can then display "10% done", "20% done" and so on. Again, the last thing you want is for your web page to look like it is hung or dead.

Sorry if it wasn't clear. Let's try it again.

In your Servlet you likely have at least a doGet() method - I'm going to guess that that is what you are showing. You need to break up the work into two different parts. Something about like:

public class ProcessService extends HttpServlet {
// in this example the Result class holds whatever the result of your compuation is
    private static HashMap<String, Result> results = new HashMap<String, Result>();
 
public void doGet(HttpServletRequest request, HttpServletResponse response) {
    String action = request.getParameter( "action" );
    if( action.equals( "processData" ) )
        processDataAndReturn( request, response );
    else if( action.equals( "getResults" ) )
        getResults( request, response );
}
 
private String processDataAndReturn(HttpServletRequest request, HttpServletResponse response) throws Exception {
    ComputationThread compThread = new ComputationThread( request.getSession().getId() );
    compThread.start();
 
    response.sendRedirect( "inProgress.jsp" );
}
 
private void getResults( HttpServletRequest request, HttpServletResponse response ) {
    Result result = results.get( request.getSession().getId() );
 
    if( result != null ) {
        // return result to browser in whatever way you do now.
    }
}
 
 
private static class ComputationThread extends Thread {
    private String sessionId;
 
    public ComputationThread( String id ) {
        sessionId = id;
    }
 
    @Override
    public void run() {
        Process1();
        Result result = Process2();
 
        results.put( sessionId, result );
    }
}
}

Now you have the framework to handle multiple simultaneous requests. The request from the user to start the process would be to a URL something like:

http://your.host.name/compute?action=processData

Then, in a JSP that shows the end user that the system is in the process of working (I called it inProgress.jsp above) you'd have some code that does:

function doPoll(){
    $.get('compute?action=getResults', function(data) {
        alert(data);  // process results here, may be empty
        setTimeout(doPoll,5000);
    });
}

This snippet of code tries to get results every 5 seconds - it polls every 5 seconds. If there are none available you would have to handle that and likely do nothing. If there are results then you show them the way you do now.

This isn't too bad to implement but there are a few moving parts. I've also left out error checking and clean up (what if a computation is started but then the user closes their browser? The result is taking memory for nothing).

Does this make any more sense?