Spring – How to do dependency injection in your session listener

Spring comes with a “ContextLoaderListener” listener to enable Spring dependency injection into session listener. In this tutorial, it revises this HttpSessionListener example by adding a Spring dependency injection a bean into the session listener.

1. Spring Beans

Create a simple counter service to print total number of sessions created.

File : CounterService.java

package com.mkyong.common;
 
public class CounterService{
 
	public void printCounter(int count){
		System.out.println("Total session created : " + count);
	}
 
}

File : counter.xml – Bean configuration file.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans 
	http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
 
	<bean id="counterService" class="com.mkyong.common.CounterService" />
 
</beans>

2. WebApplicationContextUtils

Uses “WebApplicationContextUtils” to get the Spring’s context, and later you can get any declared Spring’s bean in a normal Spring’s way.

File : SessionCounterListener.java

package com.mkyong.common;
 
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
 
public class SessionCounterListener implements HttpSessionListener {
 
     private static int totalActiveSessions;
 
     public static int getTotalActiveSession(){
           return totalActiveSessions;
     }
 
    @Override
    public void sessionCreated(HttpSessionEvent arg0) {
           totalActiveSessions++;
           System.out.println("sessionCreated - add one session into counter");	
           printCounter(arg0);
    }
 
    @Override
    public void sessionDestroyed(HttpSessionEvent arg0) {
           totalActiveSessions--;
           System.out.println("sessionDestroyed - deduct one session from counter");	
           printCounter(arg0);
    }	
 
    private void printCounter(HttpSessionEvent sessionEvent){
 
          HttpSession session = sessionEvent.getSession();
 
          ApplicationContext ctx = 
                WebApplicationContextUtils.
                      getWebApplicationContext(session.getServletContext());
 
          CounterService counterService = 
                      (CounterService) ctx.getBean("counterService");
 
          counterService.printCounter(totalActiveSessions);
    }
}

3. Integration

The only problem is, how your web application know where to load the Spring bean configuration file? The secret is inside the “web.xml” file.

  1. Register “ContextLoaderListener” as the first listener to make your web application aware of the Spring context loader.
  2. Configure the “contextConfigLocation” and define your Spring’s bean configuration file.

File : web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >
 
<web-app>
  <display-name>Archetype Created Web Application</display-name>
 
  <context-param>
	<param-name>contextConfigLocation</param-name>
	<param-value>/WEB-INF/Spring/counter.xml</param-value>
  </context-param>
 
  <listener>
        <listener-class>
            org.springframework.web.context.ContextLoaderListener
        </listener-class>
  </listener>
 
  <listener>
	<listener-class>
            com.mkyong.common.SessionCounterListener
        </listener-class>
  </listener>
 
  <servlet>
	<servlet-name>Spring DI Servlet Listener</servlet-name>
	<servlet-class>com.mkyong.common.App</servlet-class>
  </servlet>
 
  <servlet-mapping>
	<servlet-name>Spring DI Servlet Listener</servlet-name>
	<url-pattern>/Demo</url-pattern>
  </servlet-mapping>
 
</web-app>

File : App.java

package com.mkyong.common;
 
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
public class App extends HttpServlet{
 
  public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws IOException{
 
        HttpSession session = request.getSession(); //sessionCreated() is executed
        session.setAttribute("url", "mkyong.com"); 
        session.invalidate();  //sessionDestroyed() is executed
 
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<body>");
        out.println("<h1>Spring Dependency Injection into Servlet Listenner</h1>");
        out.println("</body>");
        out.println("</html>");	
 
   }
}

Start Tomcat, and access the URL “http://localhost:8080/SpringWebExample/Demo“.

output

sessionCreated - add one session into counter
Total session created : 1
sessionDestroyed - deduct one session from counter
Total session created : 0

See the console output, you get the counter service bean via Spring DI, and print the total number of sessions.

Conclusion

In Spring, the “ContextLoaderListener” is a generic way to integrate Spring Dependency Injection to almost all of the web application.

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About the Author

mkyong
Founder of Mkyong.com and HostingCompass.com, love Java and open source stuff. Follow him on Twitter, or befriend him on Facebook or Google Plus. If you like my tutorials, consider make a donation to these charities.

Comments

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  • Mudit

    Hi ,

    I have problem in maintaining session in Springs. I first user logs in to the application and then the second users logs in . The First user is geeting the data of the second user.

    I did the google … but didn’t got any help ..

    Pls help

  • James Watkins

    I know this is only an example, but static variables should never be used in listeners like this, because they will cause unexpected behavior when you hit a production environment. A reliable data source should be used to keep track of counting sessions. However, this is a simple example and data sources are out of scope. Just remember don’t use static in production code.

  • http://www.mkyoung.com Raghunandana

    Sir,How to validate sessions in normal spring web application without using spring security

  • AT

    Hi ,

    Is There a way to set dependencies here ?
    For example , if the loading of my xml in contextConfigLocation depends on a spring remote service , Can I tell the listener to wait till the remote service is available ?

  • Adochiny

    Lovely thanks for sharing.

  • Sebastian

    Hi mkyong!

    Is it possible to inject the “CounterService” with annotations? I would prefer something like that:

    package com.mkyong.common;
     
    import javax.servlet.http.HttpSession;
    import javax.servlet.http.HttpSessionEvent;
    import javax.servlet.http.HttpSessionListener;
    import org.springframework.context.ApplicationContext;
    import org.springframework.web.context.support.WebApplicationContextUtils;
     
    public class SessionCounterListener implements HttpSessionListener {
     
         private static int totalActiveSessions;
     
         @Autowired
         private CounterService counterService;
     
         public static int getTotalActiveSession(){
               return totalActiveSessions;
         }
     
        @Override
        public void sessionCreated(HttpSessionEvent arg0) {
               totalActiveSessions++;
               System.out.println("sessionCreated - add one session into counter");	
               printCounter(arg0);
        }
     
        @Override
        public void sessionDestroyed(HttpSessionEvent arg0) {
               totalActiveSessions--;
               System.out.println("sessionDestroyed - deduct one session from counter");	
               printCounter(arg0);
        }	
     
        private void printCounter(HttpSessionEvent sessionEvent){
              HttpSession session = sessionEvent.getSession();
              counterService.printCounter(totalActiveSessions);
        }
     
        public void setCounterService(CounterService counterService) {
              this.counterService = counterService;
        }
     
        public CounterService getCounterService() {
              return counterService;
        }
    }

    I didn’t get it with @Autowired. I also tried to annotate the class with @Component and I configured the following in my Spring configuration:

     

    Do you have an idea?

    Best regards,
    Sebastian

    PS: Very good pages!

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  • suresh

    org.postgresql.util.PSQLException: ERROR: relation “qrtz_locks” does not exist

    i am getting this error ,, any comment

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  • Emmanuel

    You can integrate Quartz in Spring on Web application by using this example?

    • http://www.mkyong.com mkyong

      This is a generic solution for almost all of the framework. But, Spring also comes with API integrate Quartz easily, see this article – http://www.mkyong.com/spring/spring-quartz-scheduler-example/

      • Vlad

        Any idea how to make DI with annotations? Tried it different ways still getting null exception on my service.

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