How to listen to Servlet containers

1. Two methods for implementing the javax. servlet. ServletContextListener interface: contextInitialized () and contextDestroyed ()

ContextInitialized (): executed when the Servlet container starts
ContextDestroyed (): executed when the Servlet container is stopped

2. Add the program to be listened to in contextInitialized (), and control the execution frequency of the listener by using the schedule () method of java. util. Timer.

DEMO: This is a prototype of my text message reply listener. It is simplified)

ReplyListener. java

 
 

  
  
package com.hanweb.jcms;  
  
  
 
  
  
import javax.servlet.*;  
  
  
 
  
  
public class ReplyListener implements ServletContextListener {  
  
  
private ReplyTimer rt = null;  
  
  
public void contextInitialized(ServletContextEvent event) {  
  
  
String status = "[SYS] SMS reply listener start .";  
  
  
event.getServletContext().log(status);  
  
  
System.out.println(status);  
  
  
 
  
  
rt = new ReplyTimer(1);  
  
  
rt.start();  
  
  
}  
  
  
 
  
  
public void contextDestroyed(ServletContextEvent event) {  
  
  
String status = "[SYS] SMS reply listener stop .";  
  
  
event.getServletContext().log(status);  
  
  
System.out.println(status);  
  
  
 
  
  
if (rt != null) {  
  
  
rt.stop();  
  
  
}  
  
  
}  
  
  
} 
 
 

ReplyTimer. java

 
 

  
  
package com.hanweb.jcms;  
  
  
 
  
  
import java.util.*;  
  
  
 
  
  
public class ReplyTimer {  
  
  
private final Timer timer = new Timer();  
  
  
private final int min;  
  
  
 
  
  
public ReplyTimer(int minutes) {  
  
  
min = minutes;  
  
  
}  
  
  
 
  
  
public void start() {  
  
  
Date date = new Date();  
  
  
timer.schedule(new ReplyTask(), date, min * 60 * 1000);  
  
  
}  
  
  
 
  
  
public void stop() {  
  
  
timer.cancel();  
  
  
}  
  
  
} 
 
 

ReplyTask. java

 
 

  
  
package com.hanweb.jcms;  
  
  
 
  
  
import java.util.*;  
  
  
 
  
  
public class ReplyTask extends TimerTask {  
  
  
public void doSomething() {  
  
  
System.out.println("[SYS] SMS reply listener running ");  
  
  
}  
  
  
 
  
  
public void run() {  
  
  
doSomething();  
  
  
}  
  
  
} 
 
 

Put the compiled class file into the WEB-INF/classes, and finally do not forget to add the listening statement to the WEB. xml of the current web application in the Servlet container:

 
 

  
  
<listener> 
  
  
<listener-class>com.hanweb.jcms.ReplyListener</listener-class> 
  
  
</listener> 
 
 

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