Java Servlet @WebListener Annotation Example

Details: Written by Nam Ha Minh; Last Updated on 26 June 2019 | Print Email

[Master REST API Development and Java and Spring Boot]

The @WebListener annotation is used to register a class as a listener of a web application. The annotated class must implement one or more of the following interfaces:

- javax.servlet.ServletContextListener
- javax.servlet.ServletContextAttributeListener
- javax.servlet.ServletRequestListener
- javax.servlet.ServletRequestAttributeListener
- javax.servlet.http.HttpSessionListener
- javax.servlet.http.HttpSessionAttributeListener

Syntax of @WebListener Annotation:

@WebListener([optional description])

Attributes of @WebListener Annotation:

Name	Type	Required	Description
value	String	Optional	Description of the listener.

Some Examples with @WebListener Annotation:

The following example code uses the @WebListenerannotation to register a class as a listener for the ServletContextListener’s events:

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class ContextListener implements ServletContextListener {

	@Override
	public void contextInitialized(ServletContextEvent event) {
		System.out.println("The application started");
	}
	
	@Override
	public void contextDestroyed(ServletContextEvent event) {
		System.out.println("The application stopped");
	}
}

The following example code registers a listener which implements two interfaces with description:

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionListener;

@WebListener("Session listener for the application")
public class MySessionListener implements HttpSessionListener,
		HttpSessionAttributeListener {

	// overrides required methods here...
}

A great application of using @WebListener is to implement hit counter for Java web applications. Read this tutorial to learn more.

Related Java Servlet Annotations:

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