1.ServletContext监听器：
用来监听ServletContext的创建与销毁
步骤：
a、编写一个监听器类去实现监听器接口
b、覆盖监听器的方法
c、需要在web.xml中进行配置---注册
public class ServletContext implements ServletContextListener { public ServletContext() { // TODO Auto-generated constructor stub } public void contextDestroyed(ServletContextEvent sce) { System.out.println("web应用销毁"); } public void contextInitialized(ServletContextEvent sce) { System.out.println("web应用初始化"); Timer t = new Timer(); t.scheduleAtFixedRate(new TimerTask() {//在ServletContext初始化时，添加定时任务 @Override public void run() { System.out.println("利息增加"); } },new Date(), 5000);//执行的任务，开始时间，间隔 } }
2.ServletContextAttributeListener ServletContext属性监听
监听ServletContext中的属性有变化（增、删、改）
public class ServletContextAttr implements ServletContextAttributeListener { public ServletContextAttr() { // TODO Auto-generated constructor stub } public void attributeAdded(ServletContextAttributeEvent scae) { System.out.println("增加属性 "); System.out.println("属性是" + scae.getName()); System.out.println("值是" + scae.getValue()); } public void attributeRemoved(ServletContextAttributeEvent scae) { System.out.println("属性移除"); } public void attributeReplaced(ServletContextAttributeEvent scae) { System.out.println("属性替换"); } }
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Insert title here</title> </head> <body> <% application.setAttribute("name","god");//添加ServletContext属性 application.setAttribute("name", "wish");//替换属性 application.removeAttribute("name");//移除属性 %> </body> </html>
3.Session监听器
用来监听Session的创建与销毁
public class Session implements HttpSessionListener { public Session() { // TODO Auto-generated constructor stub } public void sessionCreated(HttpSessionEvent se) { String s = se.getSession().getId(); System.out.println("session被创建，ID为："+s); } public void sessionDestroyed(HttpSessionEvent se) { System.out.println("session被销毁); } }
在线人数统计：
public class OnlineNumberListener implements HttpSessionListener{ @Override public void sessionCreated(HttpSessionEvent e) { ServletContext application = e.getSession().getServletContext(); Integer onlinenumber = (Integer)application.getAttribute("onlinenumber"); if(onlinenumber==null) { onlinenumber = 0; } onlinenumber++; application.setAttribute("onlinenumber", onlinenumber); System.out.println("新增一位在线用户"); } @Override public void sessionDestroyed(HttpSessionEvent e) { ServletContext application = e.getSession().getServletContext(); Integer online_number = (Integer) application.getAttribute("online_number"); if(null==online_number){ online_number = 0; } else online_number--; application.setAttribute("online_number", online_number); System.out.println("一位用户离线"); } }
4.Request监听器
public class Request implements ServletRequestListener { public Request() { // TODO Auto-generated constructor stub } public void requestDestroyed(ServletRequestEvent sre) { System.out.println("请求销毁"); } public void requestInitialized(ServletRequestEvent sre) { String p = sre.getServletRequest().getParameter("name"); System.out.println("收到请求，请求值为："+p); } }
总结：ServletContext Session Request 都可以实现各自的Listener接口，也可以实现各自的AttributeListener接口，重写方法即可。
5.绑定监听
HttpSessionBindingListener接口，可以监听对象是否被绑定至Session内
public class Person implements HttpSessionBindingListener{ private String name; private int age; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public void valueBound(HttpSessionBindingEvent event) { System.out.println("Person对象绑定至session域"); } @Override public void valueUnbound(HttpSessionBindingEvent event) { System.out.println("Person对象从session域中解绑"); } }
HttpSession session = request.getSession(); Person p = new Person(); session.setAttribute("person", p); session.removeAttribute("person");
6.钝化与活化
Session对象长期不使用时可以写入到本地磁盘，即钝化，下次访问时在写回session中，即活化
需要同时实现HttpSessionActivationListener,Serializable两个接口
public class Car implements HttpSessionActivationListener,Serializable{ private static final long serialVersionUID = 1L; private String color; private String brand; public String getColor() { return color; } public void setColor(String color) { this.color = color; } public String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } @Override public void sessionWillPassivate(HttpSessionEvent se) { System.out.println("Car被钝化"); } @Override public void sessionDidActivate(HttpSessionEvent se) { System.out.println("Car被活化"); } }
HttpSession session = request.getSession(); Car c = new Car(); c.setColor("red"); session.setAttribute("car", c); System.out.println("Car被添加到session中");
自定义配置：
在WebContent/META-INF下创建context.xml
<?xml version="1.0" encoding="UTF-8"?> <Context> <!-- maxIdleSwap:session中的对象多长时间不使用就钝化 --> <!-- directory:钝化后的对象的文件写到磁盘的哪个目录下 配置钝化的对象文件在work/catalina/localhost/钝化文件 --> <Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1"> <Store className="org.apache.catalina.session.FileStore" directory="demo" /> </Manager> </Context>