"Online Tweeter Enterprise Application" : Creating a Singleton Session Bean in NetBeans EJB module - Part 7

Lets continue building "Online Tweeter Enterprise Application" in NetBeans. In this section of tutorial, you will create a Singleton Session Bean by name "ActiveFollowersOnline.java". A Singleton Session Bean is a enterprise bean which are instantiated once per application and has lifecycle till application is alive.

Step 1: Open "Tweeter-war" project and right click Source Packages and then select New and than Other as shown in fig below:

Step 2: On clicking Other a dialog box appears by name New File. In the Categories: list select Enterprise JavaBeans and in the File Types: select Session Bean as shown in fig below.

Step 3: Click

.
New Session Bean dialog box gets open. It prompts us to enter EJB Name: , Project: , Location: , Package: , Session Type: and Create Interface: etc. Enter the values as shown in the fig below.

Step 4: Click

 
A new Singleton Session Bean gets created by name "ActiveFollowersOnline.java" in the "Tweeter-war" module in the package provided at the time of creating the bean. It has most of the source code already generated by NetBeans. Kindly add or remove additional code provided below.

package com.hubberspot.ejb;

import javax.ejb.Singleton;
import javax.ejb.LocalBean;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

// @Singleton annotation informs container that
// treat this bean as a Singleton bean.

// @LocalBean annotation informs container that
// this session bean exposes a no-interface view.

// @WebListener annotation informs container that
// this class is a web listener which will listen to 
// various events happening during lifecyle of application
// Here this class listens to Http Session when a session
// is created or destroyed.

// We make class implements HttpSessionListener which has two
// methods sessionCreated() and sessionDestroyed() , which 
// are called by the container whenever a session is created 
// or destroyed

@Singleton
@LocalBean
@WebListener
public class ActiveFollowersOnline implements HttpSessionListener {

    private static int followersOnline = 0;

    @Override
    public void sessionCreated(HttpSessionEvent se) {
        
        System.out.print("Session Created : ");
        followersOnline++;
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        followersOnline--;
    }

    public int getFollowersOnline() {
        return followersOnline;
    }   
    
}

In the next section of this blog (part 8) you will learn how to create a Servlet in NetBeans for this application in the Web module.