Running a java "background application" in application server

Question

My experience with application servers is limited to some basic servlet coding, so I am not even sure how to frame this question appropriately.

I need to write a java program that runs on the (java) application server and continuously executes a certain method (it will check for files in a certain directory).

I have found a way to schedule the start of applications but need to know where to put the code that I would normally put in the main() method in a regular java program.

Answer 1

I asked a similar question on this a long time ago: http://stackoverflow.com/questions/48293/running-a-regular-background-event-in-java-web-app

Answer 2

Take a look at the servlet event listeners.

I think you should be able to hook into your code using a ServletContextListener.

http://onjava.com/pub/a/onjava/2001/04/12/listeners.html

Answer 3

You can use Quartz, or the EJB timer service (if you can learn EJBs) for this task.

If you have just a servlet container like Tomcat, it is preferable to go with Quartz. In fact, Quartz also comes with a web application to monitor a scheduler.

On the other hand, the EJB timer service is available in all EJB containers that support EJB 2.1 and above.

Answer 4

Not answering straight to your question, but check out Spring Batch that could be useful.

Answer 5

One way of doing this is to write a Listener which implements ServletContextListener and you write you schedule your timer in contextInitialized method

Answer 6

You MUST let the web container manage your threads!

Read the specification for web.xml carefully - what you need is in there.