Wicket: how to handle long running tasks

Question

Hey all,

I've setup a Wicket + Hibernate + Spring Web application that involves gathering some data (having some files generated and returned), storing this in a database, creating some images and displaying all this on a webpage.

This all works fine for short runs, but sometimes gathering the data (which involves some remote number crunching) takes too long (20+ minutes) and times out. I've tried to resolve this using two approaches, but both of them show some problems.

The first approach was using AjaxLazyLoadPanels and just doing everything within the getLazyLoadComponent. This worked fine for the short runs, but for the 20+ minute runs the LazyLoadComponents would not load (nice oxymoron there) due to timeouts.

The second approach involved creating an intermediate Fragment with an added AjaxSelfUpdatingTimerBehavior with a duration set to 10 seconds, that polled for the files that are created in the number crunching. This seems to make the tasks run in the background without problems, but fails when the returned data needs to be stored in the database. I'm using the Open Session in View pattern, but maybe this fails when attempting to store data after 20 minutes?? (Solution could lie in resolving this..).

Due to the above problems I'm now reading up on alternate approaches to handle these long running tasks and came across:

• org.apache.wicket.util.time.Task
• org.apache.wicket.util.watch.ModificationWatcher

I'm now wondering if either of these might be better suited to solve the time-out problems I'm having in both running the tasks and storing the data in the database afterwards, or if anyone has any other solutions that might help in this situation.

I'd really like to know if a new approach is viable before I spend another day implementing something that might turn out not to work after all.

Best regards,
Tim

Answer 1

I know we have had success in using a Panel with an attached AjaxSelfUpdatingTimerBehavior. The task and the results piece are separated from the view logic, but are made accessible for the view via a service you create. The service implementation we have used is then responsible for starting a TheadPool or ExectutorService for running the individual tasks. The service can provide a way to monitor the progress/status of the particular job/call that is taking place. Once it is complete it should also make the data available for the view. Injection of a SessionFactory into the service implementation (or injected DAO) should be sufficient to create the HibernateSession outside of a WebSession.