三大域的监听器
一，对三大域对象创建和销毁的监听：
1.ServletRequestListener ：对请求创建和销毁的监听，在客户端发送请求时创建，发送完毕后销毁。
2.HttpSessionListener ：session创建时监听，session销毁时(设置session存活时间或使用session.invalidate()方法)监听。
3.ServletContextListener ：application创建时监听（即web应用启动时），application销毁时监听（即服务器关闭时监听）。
二，对三大域对象进行添加，修改，删除属性值的监听
1.ServletRequestAttributeListener
2.HttpSessionAttributeListener
3.ServletContextAttributeListener
以下的三个方法对应着三大域对象对属性操作的监听
@Override
public void attributeAdded(ServletRequestAttributeEvent arg0) {
System.out.println("向request中添加属性"+arg0.getName()+"="+arg0.getValue());
}
@Override
public void attributeRemoved(ServletRequestAttributeEvent arg0) {
// TODO Auto-generated method stub
System.out.println("从request中删除属性"+arg0.getName()+"="+arg0.getValue());
}
@Override
public void attributeReplaced(ServletRequestAttributeEvent arg0) {
// TODO Auto-generated method stub
System.out.println("重置request中的属性"+arg0.getName()+"="+arg0.getValue());
}
监听步骤：
1.定义监听器。实现需要监听的事件的接口
MyRequestAttrbuteListener.java
package com.javaweb.listener;
import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;
public class MyRequestAttrbuteListener implements
ServletRequestAttributeListener {
@Override
public void attributeAdded(ServletRequestAttributeEvent arg0) {
System.out.println("向request中添加属性"+arg0.getName()+"="+arg0.getValue());
}
@Override
public void attributeRemoved(ServletRequestAttributeEvent arg0) {
// TODO Auto-generated method stub
System.out.println("从request中删除属性"+arg0.getName()+"="+arg0.getValue());
}
@Override
public void attributeReplaced(ServletRequestAttributeEvent arg0) {
// TODO Auto-generated method stub
System.out.println("重置request中的属性"+arg0.getName()+"="+arg0.getValue());
}
}
2.注册监听器
web.xml
<listener>
<listener-class>com.javaweb.listener.MyRequestAttrbuteListener</listener-class>
</listener>
3.触发事件
<body>
show.jsp
<%
request.setAttribute("username", "hahah");
request.setAttribute("username", "hehei");
request.removeAttribute("username");
%>
</body>
对Session的对象属性进行解绑和绑定监听
1.对象类实现HttpSessionBindingListener接口，但是不需要我们自己去注册监听器。
package com.javaweb.beans;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
public class Student implements HttpSessionBindingListener{
private int age;
private String name;
public Student() {
super();
}
public Student(int age, String name) {
super();
this.age = age;
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student [age=" + age + ", name=" + name + "]";
}
@Override
public void valueBound(HttpSessionBindingEvent arg0) {
// TODO Auto-generated method stub
System.out.println("session 绑定对象"+arg0.getName()+"="+arg0.getValue());
}
@Override
public void valueUnbound(HttpSessionBindingEvent arg0) {
// TODO Auto-generated method stub
System.out.println("session 解绑对象"+arg0.getName()+"="+arg0.getValue());
}
}
2.触发事件
<%
session.setAttribute("stu", new Student(11,"aaa"));
session.removeAttribute("stu");
%>
对Session的对象进行活化和钝化
活化：把对象从硬盘写到服务器。
钝化：把对象从服务器写到硬盘。
活化和钝化对应着对象的反序列化和序列化，所有我们实现监听时，必须实现Serializable接口。不需要注册监听器。
1.定义监听器
package com.javaweb.beans;
import java.io.Serializable;
import javax.servlet.http.HttpSessionActivationListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
import javax.servlet.http.HttpSessionEvent;
public class Student implements HttpSessionActivationListener,Serializable{
private int age;
private String name;
public Student() {
super();
}
public Student(int age, String name) {
super();
this.age = age;
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student [age=" + age + ", name=" + name + "]";
}
@Override
public void sessionDidActivate(HttpSessionEvent arg0) {
// TODO Auto-generated method stub
System.out.println("对象活化");
}
@Override
public void sessionWillPassivate(HttpSessionEvent arg0) {
// TODO Auto-generated method stub
System.out.println("对象将要钝化");
}
}
2。触发条件
活化触发情况：服务器重启
钝化触发情况：服务器停掉
