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.
- Register “
ContextLoaderListener” as the first listener to make your web application aware of the Spring context loader. - 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.
Hi,
I am trying to add the dependency of a spring managed class into my cutstom HTTPSessionListener. I have removed the listener entry from web.xml. sessionDestroyed method is getting called after any session expires but the dependency of xUserMgr is null hence it gives NULLPOINTEREXCEPTIN while calling – updateIsActiveStatusOfLoggedInUserWithHTTPSession.
@Component
public class RangerHttpSessionListener implements HttpSessionListener,ApplicationContextAware {
@Autowired
XUserMgr xUserMgr;
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
if (applicationContext instanceof WebApplicationContext) {
((WebApplicationContext) applicationContext).getServletContext().addListener(this);
} else {
//Either throw an exception or fail gracefully, up to you
throw new RuntimeException(“Must be inside a web application context”);
}
}
private static CopyOnWriteArrayList listOfSession = new CopyOnWriteArrayList();
@Override
public void sessionCreated(HttpSessionEvent event) {
listOfSession.add(event.getSession());
}
@Override
public void sessionDestroyed(HttpSessionEvent event) {
if (!listOfSession.isEmpty()) {
updateIsActiveStatusForAuthSession(event.getSession());
listOfSession.remove(event.getSession());
}
}
private void updateIsActiveStatusForAuthSession(HttpSession session) {
xUserMgr.updateIsActiveStatusOfLoggedInUserWithHTTPSession(session.getId(),1);
}
public static CopyOnWriteArrayList getActiveSessionOnServer() {
return listOfSession;
}
}
Hi,
I’m trying to run a sql delete in my session listener using spring4
Using HttpSession session = sessionEvent.getSession();
ApplicationContext ctx =
WebApplicationContextUtils.
getWebApplicationContext(session.getServletContext());
PatientService pService =
(PatientService) ctx.getBean(“patientService”);
I can access my service, which has access to my dao objects.
However my dao objects are always null.
Is there any way of accessing my dao objects from within a session listener?
Any help would be greatly appreciated.
Thanks
Hey MKyong. Thanks for the wonderful tutorial. I am currently learning Spring. I had one doubt. In the
SessionCounterListener bean you are using HttpSessionListener and getting the “counterservice” bean using
web application utils. Cant we do the same using ApplicationContextAware along with HTTPSessionListener
as aplicationcontextaware also returns the application context and using that also we can get the counterservice bean.
(Correct me if i am wrong).
I thank you for this tuto but You can precise why we use the listener in Spring application
Call this function in your session listener to make the ‘Autowired’ annotation work:
SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);
Thx 🙂 works
Thanks for the post
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
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.
Sir,How to validate sessions in normal spring web application without using spring security
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 ?
Lovely thanks for sharing.
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!
org.postgresql.util.PSQLException: ERROR: relation “qrtz_locks” does not exist
i am getting this error ,, any comment
This article is nothing to do with the Postgresql database development, it’s about DI in session listener.
Blind guess, using quartz scheduler right? may be you can check this article https://mkyong.com/spring/spring-quartz-scheduler-example/
You can integrate Quartz in Spring on Web application by using this example?
This is a generic solution for almost all of the framework. But, Spring also comes with API integrate Quartz easily, see this article – https://mkyong.com/spring/spring-quartz-scheduler-example/
Any idea how to make DI with annotations? Tried it different ways still getting null exception on my service.