ServletContextListener Example

This tips explains the how to use ServletContextListener. There will be only one ServletContext for each web application. ServletContext will be created while deploying the application. Once the ServletContext is created, it will be used by all the servlets and jsp files in the same application. ServletContext is also called as the application scope variables in the web application scenario.

also read:

• Java EE Tutorials
• Servlets Interview Questions
• New Features in Servlets 3.0
• Asynchronous Servlets in Servlets 3

ServletContextListener has the following two methods:

• public void contextInitialized(ServletContextEvent event)
• public void contextDestroyed(ServletContextEvent event)

Look into the following example for how to implement the ServletContextListener methods:

ServletContextExample.java

[code lang=”java”]
package example;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class ServletContextExample implements ServletContextListener{
ServletContext context;
public void contextInitialized(ServletContextEvent contextEvent) {
System.out.println("Context Created");
context = contextEvent.getServletContext();
// set variable to servlet context
context.setAttribute("TEST", "TEST_VALUE");
}
public void contextDestroyed(ServletContextEvent contextEvent) {
context = contextEvent.getServletContext();
System.out.println("Context Destroyed");
}
}
[/code]

web.xml

[code lang=”xml”]
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<listener>
<listener-class>
example.ServletContextExample
</listener-class>
</listener>
</web-app>
[/code]

In the above example ServletContextExample implements ServletContextListener. It has two methods contextInitialized which is called when the ServletContext is created. Another one is contextDestroyed which is called while context is destroyed, this happens normally when web server is shut down or crash.