Can some code run when we first deploy a WAR file?

tomcat, web-deployment

Solution

Reviving an old question since the only answer doesn't show any example.

In order to run a custom piece of code whenever a web application WAR is deployed/undeployed or Tomcat is started/stopped, you need to:

- Implement the `ServletContextListener` listener and its methods `contextInitialized()` and `contextDestroyed()`.

- Let Tomcat know about your implementation. According to the documentation, you can either add the implementing class to the deployment descriptor, annotate it with `WebListener`, or register it via one of the `addListener()` methods defined on `ServletContext`.

Here is an example (based on this post):

package com.example;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyServletContextListener implements ServletContextListener {
    /** The servlet context with which we are associated. */
    private ServletContext context = null;

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        log("Context destroyed");
        this.context = null;
    }

    @Override
    public void contextInitialized(ServletContextEvent event) {
        this.context = event.getServletContext();
        log("Context initialized");
    }

    private void log(String message) {
        if (context != null) {
            context.log("MyServletContextListener: " + message);
        } else {
            System.out.println("MyServletContextListener: " + message);
        }
    }
}

And add the following to `web.xml` (or alternatively, use the `WebListener` annotation or `addListener()` method):

<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    ...
    <listener>
        <listener-class>com.example.MyServletContextListener</listener-class>
    </listener>
</web-app>

Problem

Original source