JSP之监听器Listener(二)

ServletContextAttributeListener

用于监听ServletContext也就是application范围内属性的变化，实现该结构主要重写三个方法

• attributeAdded()方法：当向application中添加参数的时候会自动调用
• attributeRemoved()方法：当把application中的参数移除的时候调用
• attributeReplaced()方法：当修改application中的参数时调用

 1 package com.huayu.listener;
 2
 3 import javax.servlet.ServletContextAttributeEvent;
 4 import javax.servlet.ServletContextAttributeListener;
 5 import javax.servlet.annotation.WebListener;
 6 @WebListener
 7 public class Listener3 implements ServletContextAttributeListener{
 8
 9     @Override
10     public void attributeAdded(ServletContextAttributeEvent event) {
11         String named=event.getName().toString();
12         String value=event.getValue().toString();
13         System.out.println("application中添加了一个"+named+"变量值为"+value);
14
15     }
16
17     @Override
18     public void attributeRemoved(ServletContextAttributeEvent event) {
19         String named=event.getName().toString();
20         String value=event.getValue().toString();
21         System.out.println("application中添移除一个"+named+"变量值为"+value);
22
23
24
25     }
26
27     @Override
28     public void attributeReplaced(ServletContextAttributeEvent event) {
29         String named=event.getName().toString();
30         String value=event.getValue().toString();
31         System.out.println("application中"+named+"变量值变为"+value);
32     }
33
34 }

ServletRequestListener

用来监听用户的请求到达，请求的结束

requestInitialized:用户请求到达，被初始化时触发该方法

requestDestroyed:用户请求结束，被销毁时触发该方法

ServletRequestAttributeListener

用来监听request范围内变量的变化

attributeAdded（）

attributeReplaced（）

attributeRemoved（）

 1 package com.huayu.listener;
 2
 3 import javax.servlet.ServletRequest;
 4 import javax.servlet.ServletRequestAttributeEvent;
 5 import javax.servlet.ServletRequestAttributeListener;
 6 import javax.servlet.ServletRequestEvent;
 7 import javax.servlet.ServletRequestListener;
 8 import javax.servlet.annotation.WebListener;
 9 import javax.servlet.http.HttpServletRequest;
10 @WebListener
11 public class Listener4 implements ServletRequestListener,ServletRequestAttributeListener{
12
13     @Override
14     public void requestDestroyed(ServletRequestEvent arg0) {
15
16         HttpServletRequest request=(HttpServletRequest) arg0.getServletRequest();
17         System.out.println("---发向"+request.getRequestURI()+"请求被销毁-----");
18
19     }
20
21     @Override
22     public void requestInitialized(ServletRequestEvent arg0) {
23         HttpServletRequest request=(HttpServletRequest) arg0.getServletRequest();
24         System.out.println("---发向"+request.getRequestURI()+"请求被初始化-----");
25     }
26
27     @Override
28     public void attributeAdded(ServletRequestAttributeEvent arg0) {
29             ServletRequest request=arg0.getServletRequest();
30             String name=arg0.getName();
31             String value=arg0.getValue().toString();
32             System.out.println(request+"范围内添加了名为"+name+"值为"+value+"的属性");
33
34     }
35
36     @Override
37     public void attributeRemoved(ServletRequestAttributeEvent arg0) {
38         ServletRequest request=arg0.getServletRequest();
39         String name=arg0.getName();
40         String value=arg0.getValue().toString();
41         System.out.println(request+"范围内添加了名为"+name+"值为"+value+"的属性被删除");
42
43     }
44
45     @Override
46     public void attributeReplaced(ServletRequestAttributeEvent arg0) {
47         ServletRequest request=arg0.getServletRequest();
48         String name=arg0.getName();
49         String value=arg0.getValue().toString();
50         System.out.println(request+"范围内添加了名为"+name+"值为"+value+"的属性被替换了");
51
52     }
53
54 }

HttpSessionListener

用于监听用户session的创建和销毁

sessionCreated(HttpSessionEvent se)：当session

被建立的时候调用

sessionDestroyed(HttpSessionEvent se)

当session没有任何客户端与之链接的时候执行

HttpSessionAttributeListener

使用方法同上