[Java]监听器（Listener）
过滤器（Filter）
https://blog.csdn.net/m0_71229255/article/details/130246404?spm=1001.2014.3001.5501
一 : Listener监听器简述
监听器就是监听某个对象的的状态变化的组件
监听器的相关概念：
-
事件源：
被监听的对象 ----- 三个域对象requestsessionservletContext -
监听器 :
监听事件源对象的状态的变化都会触发监听器 -
注册监听器 :
将监听器与事件源进行绑定 -
响应行为 :
监听器监听到事件源的状态变化时 所涉及的功能代码
二 : 监听器的种类
- 按照被监听的对象划分：ServletRequest域 HttpSession域 ServletContext域
- 监听的内容分：监听域对象的创建与销毁的 监听域对象的属性变化的
| ................................... | ServletContext域 | HttpSession域 | ServletRequest域 |
|---|---|---|---|
| 域对象的创建于销毁 | servletContextListener | HttpSessionListener | ServletRequestListener |
| 域对象内的属性的变化 | ServletContextAttributeListener | HttpSessionAttributeListener | ServletRequestAttributeListener |
三 : 监听三大域对象的创建与销毁的监听器
( 1 )监听ServletContext域的创建与销毁的监听器ServletContextListener
监听编写步骤 :
① : 编写一个监听器类去实现监听器接口
public class MyServletContextListener implements ServletContextListener
② : 覆盖监听器的方法
@Override
public void contextInitialized(ServletContextEvent sce) {
System.out.println("context创建了....");
}
@Override
public void contextDestroyed(ServletContextEvent sce) {
System.out.println("context销毁了");
}
③ : 在web.xml中进行配置
com.TianTian.atrribute.MyServletContextAttributeListener
ServletContextListener监听器的主要作用
① : 初始化的工作 ,初始化对象,初始化数据,加载数据驱动,连接池的初始化
② : 加载一下初始化的配置文件,如Spring的配置文件
③ : 任务调度---定时器---Timer/TimerTask
Timer timer = new Timer();
//task:任务 firstTime：第一次执行时间 period：间隔执行时间
//timer.scheduleAtFixedRate(task, firstTime, period);
String currentTime = "2018-10-11 18:11:00";
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date parse = null;
try {
parse = format.parse(currentTime);
} catch (ParseException e) {
e.printStackTrace();
}
timer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
System.out.println("do something.....");
}
} , parse, 24*60*60*1000);
( 2 )监听HttpSession域的创建与销毁的监听器HttpSessionListener
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class MySessionListener implements HttpSessionListener{
@Override
public void sessionCreated(HttpSessionEvent se) {
System.out.println("sessionId : " + se.getSession().getId());
}
@Override
public void sessionDestroyed(HttpSessionEvent se) {
}
}
( 3 )监听ServletRequest域创建与销毁的监听器ServletRequestListener
public class MyServletRequestListener implements ServletRequestListener{
@Override
public void requestDestroyed(ServletRequestEvent sre) {
System.out.println("销毁");
}
@Override
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("创建");
}
}
四 : 监听三大域对象的属性变化的
( 1 )域对象的通用方法
-
setAttribute(name,value) 触发添加属性/修改属性的监听器的方法
-
getAttribute(name) 触发获取属性的监听方法
-
removeAttribute(name) 触发删除属性的监听器的方法
( 2 )ServletContextAttributeLisener监听器
public class MyServletContextAttributeListener implements ServletContextAttributeListener{
@Override
public void attributeAdded(ServletContextAttributeEvent scab) {
//放到域中的属性
System.out.println("+++++监听放入");
System.out.println(scab.getName());//放到域中的name
System.out.println(scab.getValue());//放到域中的value
}
@Override
public void attributeRemoved(ServletContextAttributeEvent scab) {
System.out.println("+++++监听修改");
System.out.println(scab.getName());//删除的域中的name
System.out.println(scab.getValue());//删除的域中的value
}
@Override
public void attributeReplaced(ServletContextAttributeEvent scab) {
System.out.println("+++++监听移除");
System.out.println(scab.getName());//获得修改前的name
System.out.println(scab.getValue());//获得修改前的value
}
测试
public class TestMyServletContextAttributeListener extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ServletContext context = this.getServletContext();
//存数据
context.setAttribute("name", "美美");
//改数据
context.setAttribute("name", "可可");
//删除数据
context.removeAttribute("name");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
(3) HttpSessionAttributeListener监听器（同上）
(4) ServletRequestAriibuteListenr监听器（同上）
五 : 对象感知监听器
即将要被绑定到Session中的对象有几种状态
- 绑定状态 : 就一个对象被放到session域中
- 解绑状态 : 被绑定的对象从session域中移除了
- 钝化状态 : 是将session内存中的对象持久化( 序列化)到磁盘
- 活化状态 : 就是将磁盘上的对象再次恢复到session内存中
(1) 绑定与解绑的监听器HttpSessionBindingListener
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
public class Person implements HttpSessionBindingListener{
private String id;
private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
//绑定
public void valueBound(HttpSessionBindingEvent event) {
System.out.println("person被绑定了");
Person per = (Person)event.getValue();
System.out.println(per.getName());
}
@Override
//解除绑定
public void valueUnbound(HttpSessionBindingEvent event) {
System.out.println("person被解绑了");
}
}
测试
public class TestPersonBindingServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
HttpSession session = request.getSession();
//将person对象绑到session中
Person p = new Person();
p.setId("100");
p.setName("思思");
session.setAttribute("person", p);
//将person对象从session中解绑
session.removeAttribute("person");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
person被绑定了
思思
person被解绑了
(2) 钝化与活化的监听器HttpSessionActivationListener
可以通过配置文件,指定对象钝化时间---对象多长时间不用被敦化
在META-INF下创建一个context.xml
创建customer类
public class Customer implements HttpSessionActivationListener,Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
private String id;
private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public void sessionWillPassivate(HttpSessionEvent se) {
//钝化
System.out.println("customer被顿化了");
}
@Override
public void sessionDidActivate(HttpSessionEvent se) {
//激活
System.out.println("customer被活化了");
}
}
测试
存
ublic class TestCustomerServlet1 extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
HttpSession session = request.getSession();
Customer customer = new Customer();
customer.setId("200");
customer.setName("狗狗");
session.setAttribute("customer", customer);
System.out.println("customer被放到session域中了");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
活化取出
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//从session域中获得customer
HttpSession session = request.getSession();
Customer customer = (Customer) session.getAttribute("customer");
System.out.println(customer.getName());
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}