Background Thread for a Tomcat servlet app [duplicate]

Question

I am not very familiar with Tomcat, in my head it is basically abstracted as a cgi server that saves the JVM between calls -- I know it can do a lot more than that, though.

I am looking for a way to launch a background thread when a Tomcat server starts, which would periodically update the Server Context (in my particular case this is a thread that listens to heartbeats from some other services and updates availability information, but one can imagine a variety of uses for this).

Is there a standard way to do this? Both the launching, and the updating/querying of the Context?

Any pointers to the relevant documentation and/or code samples would be much appreciated.

Answer 1

If you want to start a thread when your WAR is deployed, you can define a context listener within the web.xml:

<web-app>     <listener>        <listener-class>com.mypackage.MyServletContextListener</listener-class>     </listener> </web-app> 

Then implement that class something like:

public class MyServletContextListener implements ServletContextListener {      private MyThreadClass myThread = null;      public void contextInitialized(ServletContextEvent sce) {         if ((myThread == null) || (!myThread.isAlive())) {             myThread = new MyThreadClass();             myThread.start();         }     }      public void contextDestroyed(ServletContextEvent sce){         try {             myThread.doShutdown();             myThread.interrupt();         } catch (Exception ex) {         }     } } 

Answer 2

I am looking for a way to launch a background thread when a Tomcat server starts

I think you are looking for a way to launch a background thread when your web application is started by Tomcat.

This can be done using a ServletContextListener. It is registered in web.xml and will be called when your app is started or stopped. You can then created (and later stop) your Thread, using the normal Java ways to create a Thread (or ExecutionService).