Run a class or method when Tomcat starts?

[Chris Stewart]

Does anyone know how I can do this? I need to fill some Hashtables when the Tomcat server is started, and only then. Can anyone help me figure out how I can run a method or class when this happens? Thanks.

[Ryan Bailey]

I'm sure there are multiple ways to do this, but one suggestion off the top of my head would be to have a servlet be instantiated when tomcat starts up. As long as you are not implementing the SingleThreadModel tomcat should not load new instances of a servlet. When declaring your servlet in your xml file be sure to include your load on startup tag in the servlet definition like this....

 <servlet>
    <servlet-name>Test</servlet-name>
    <servlet-class>TestServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet> 

This will cause the servlet to be instantiated and loaded into memory when tomcat starts. Therefore you could include some functionality in the servlet's init() method that could load data into a hashtable.
If you are implementing the SingleThreadModel than you will have to be careful doing this since the Tomcat Container can instantiate multiple servlets of the same class.
Hope this helps.
Cheers,
Ryan

[Jason Brawner]

Another way would be to write a bean that implements a ServletContextListener. When you context is loaded by tomcat (when it starts) it will create an instance of your bean and call this method:

    public void contextInitialized(ServletContextEvent event)

You must have an entry like the following in your deployment descriptor:

<listener>
  <listener-class>com.jeb.bean.ContextBean</listener-class>
</listener>

[Ryan Bailey]

Great Point Jason,
Now that I have my SCWCD I would of used the same idea Better if going to be implementing the SingleThreadModel.
Cheers,
Ryan