監聽器Listener
阿新 • • 發佈：2018-05-19
odi car schedule zab list time charset xid tee
1.ServletContext監聽器：
用來監聽ServletContext的創建與銷毀
步驟：
a、編寫一個監聽器類去實現監聽器接口
b、覆蓋監聽器的方法
c、需要在web.xml中進行配置---註冊
public class ServletContext implements ServletContextListener { public ServletContext() { // TODO Auto-generated constructor stub } public void contextDestroyed(ServletContextEvent sce) { System.out.println("web應用銷毀"); } public void contextInitialized(ServletContextEvent sce) { System.out.println("web應用初始化"); Timer t = new Timer(); t.scheduleAtFixedRate(new TimerTask() {//在ServletContext初始化時，添加定時任務 @Override public void run() { System.out.println("利息增加"); } },new Date(), 5000);//執行的任務，開始時間，間隔 } }
2.ServletContextAttributeListener ServletContext屬性監聽
監聽ServletContext中的屬性有變化（增、刪、改）
public class ServletContextAttr implements ServletContextAttributeListener { public ServletContextAttr() { // TODO Auto-generated constructor stub} public void attributeAdded(ServletContextAttributeEvent scae) { System.out.println("增加屬性 "); System.out.println("屬性是" + scae.getName()); System.out.println("值是" + scae.getValue()); } public void attributeRemoved(ServletContextAttributeEvent scae) { System.out.println("屬性移除"); } public void attributeReplaced(ServletContextAttributeEvent scae) { System.out.println("屬性替換"); } }
<%@ 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屬性 application.setAttribute("name", "wish");//替換屬性 application.removeAttribute("name");//移除屬性 %> </body> </html>
3.Session監聽器
用來監聽Session的創建與銷毀
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被創建，ID為："+s); } public void sessionDestroyed(HttpSessionEvent se) { System.out.println("session被銷毀); } }
在線人數統計：
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("新增一位在線用戶"); } @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("一位用戶離線"); } }
4.Request監聽器
public class Request implements ServletRequestListener { public Request() { // TODO Auto-generated constructor stub } public void requestDestroyed(ServletRequestEvent sre) { System.out.println("請求銷毀"); } public void requestInitialized(ServletRequestEvent sre) { String p = sre.getServletRequest().getParameter("name"); System.out.println("收到請求，請求值為："+p); } }
總結：ServletContext Session Request 都可以實現各自的Listener接口，也可以實現各自的AttributeListener接口，重寫方法即可。
5.綁定監聽
HttpSessionBindingListener接口，可以監聽對象是否被綁定至Session內
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對象綁定至session域"); } @Override public void valueUnbound(HttpSessionBindingEvent event) { System.out.println("Person對象從session域中解綁"); } }
HttpSession session = request.getSession(); Person p = new Person(); session.setAttribute("person", p); session.removeAttribute("person");
6.鈍化與活化
Session對象長期不使用時可以寫入到本地磁盤，即鈍化，下次訪問時在寫回session中，即活化
需要同時實現HttpSessionActivationListener,Serializable兩個接口
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被鈍化"); } @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");
自定義配置：
在WebContent/META-INF下創建context.xml
<?xml version="1.0" encoding="UTF-8"?> <Context> <!-- maxIdleSwap:session中的對象多長時間不使用就鈍化 --> <!-- directory:鈍化後的對象的文件寫到磁盤的哪個目錄下 配置鈍化的對象文件在work/catalina/localhost/鈍化文件 --> <Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1"> <Store className="org.apache.catalina.session.FileStore" directory="demo" /> </Manager> </Context>
監聽器Listener