listener overview
- (1) What is a listener?
Listener is used to monitor domain objects - (2) What is a domain object?
HttpServletContext HtttpSession HttpRequest HttpPageContext - (3) Analogy, the head
teacher monitors the status of students - (4) What are the listeners?
Listener monitors the creation and destruction of
domain objects - (5) What are the characteristics
"1 No listening address
" 2 Different objects use different listeners
Use of listener
- (1) Idea creates a listener
- (2) Analog Servlet and Filter
src\com.wzx.pack06_listener\TestDemo.java
public class TestDemo {
public static void main(String[] args) {
Timer timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
System.out.println("时间到了");
}
}, 5000,2000); //5秒之后执行run方法，每隔2秒再执行 run方法
}
}
src\com.wzx.pack06_listener\Demo1Listener.java
@WebListener()
public class Demo1Listener implements ServletContextListener{
public Demo1Listener() {
}
//这个方法用来监听ServletContext域的创建
/*
这个域：服务器启动时创建
*/
public void contextInitialized(ServletContextEvent sce) {
//设置一个定时器
Timer timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
try {
System.out.println("--定时发送邮件");
} catch (Exception e) {
e.printStackTrace();
}
}
}, 5000, 2000);
System.out.println("ServletContext域的创建啦");
}
//这个方法用来监听ServletContext域的销毁
/*
这个域：服务器关闭时销毁
*/
public void contextDestroyed(ServletContextEvent sce) {
System.out.println("ServletContext域销毁啦");
}
}