Start Listener AFTER Tomcat startup?

Question

I used this code to start a listener before Tomcat initializes, but it has a while loop in it that will check a database every 5 seconds for changes. Is there any way that I can skip the looping part of that until my web service has been started completely, then trigger the loop to begin checking?

EDIT: Meant listener and not Servlet

EDIT2: Code below

public class DatabaseChecker implements ServletContextListener {

final static String URL = "redacted";
final static String USER = "redacted";
final static String PASS = "redacted";

@Override
public void contextInitialized(ServletContextEvent event) {

    Vector<String> completedJobs = new Vector<String>();

    try {
        while(true) {   // loop to always check & notify
            Thread.sleep(5000);
            System.out.println("Checker running ...");
            // completedJobs = selectCompletedJobs();

        }
    } catch (Exception e) {
        e.printStackTrace();
    }

}

@Override
public void contextDestroyed(ServletContextEvent arg0) {
    System.out.println("ServletContextListener destroyed");

}

}

That's just wrong. The while loop is going to prevent the context listener from ever finishing, and thus your application will probably remain in a not-initialized state. The sleeping-busy while loop should probably be happening in a separate background thread. Like so: http://stackoverflow.com/questions/4691132/how-to-run-a-background-task-in-a-servlet-application — Gimby, Oct 01 '15 at 16:15
@Gimby that worked!!! Wanna make that an answer so I can give you that checkmark? ;) — xtheking, Oct 01 '15 at 16:35
the fact that another question+answer entirely answers yours makes your question a duplicate. Hence BalusC correctly did the paperwork. — Gimby, Oct 02 '15 at 07:36

sh0rug0ru · Answer 1 · 2015-10-01T16:13:45.697

0

Yes. The ServletContext allows you to add attributes, which is a global context shared between the ServletContextListener and the services running in the servlet.

You can have the ServletContextListener wait for the web service by polling for an attribute.

When your web service is ready, it can add the attribute to the ServletContext.

Now when your ServletContextListener finds the attribute, it can proceed.

edited Oct 01 '15 at 16:13

answered Oct 01 '15 at 16:12

sh0rug0ru

1,496
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I edited the OP to reflect my code. Should I make changes there or in my `web.xml`? – xtheking Oct 01 '15 at 16:13
These are code changes. You have to add the polling to `DatabaseChecker`. – sh0rug0ru Oct 01 '15 at 16:14

Start Listener AFTER Tomcat startup?

1 Answers1