I have a jsf app using tomcat 6, myfaces, richfaces and tomahawk.
On a page of my application a user can select several clientes (say 100 or 200) and send them an email. This email is automatically costomized for each client using tags like @name@ or @susname@. So, when a user click send, my app have to call to send function for seveal emails (say 100 or 200). This is very time expensive, so i can't make the user to wait until his request is complete. With this scenario, i want to have a batch process that do all this work transparently while the user continue working with the webapp and thinking that the emails have been sent yet.
Whenever I need to perform a long-running function in Enterprise Java, I use what I call a "null servlet".
A null servlet is a servlet that has no action processors (doGet, doPost). Instead, it simply has an init() method that spawns a thread or threads to run the long-running processes in.
Most commonly, this thread (or a dispatcher, if there are multiple threads) will pull requests from a work queue, and the UI part of the webapp will place the requests into the work queue. I may include a request monitoring component as well. Since there are multi-threading concerns here, the work queue is a synchronized data structure.
UI requests may not spawn threads themselves, and it's usually not safe for monitoring components such as session listeners to do so either. But the null servlet is a tried-and-true solution.
One final caveat. Be sure that there's a way to inform the null servlet's threads of server shutdown requests, or they won't let the server terminate.
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Lügensturm - A barrage of Blitzlügen fired in such quick succession that it is essentially impossible to correct them all.
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