Listener的使用（监听ServletContext范围内属性的改变）-优快云博客

监听ServletContext范围（application）内属性的改变，需要实现ServletContextAttributeListener接口。

1. 实现ServletContextAttributeListener接口，MyServletContextAttributeListener.java

package test;
import javax.servlet.*;
public class MyServletContextAttributeListener implements ServletContextAttributeListener{
//当程序向application范围添加属性时触发该方法
public void attributeAdded(ServletContextAttributeEvent event){
ServletContext application = event.getServletContext();
//获取添加的属性名和属性值
String name = event.getName();
Object value = event.getValue();
System.out.println(application + "范围内添加了名为" + name + "，值为" + value + "的属性!");
}
//当程序从application范围删除属性时触发该方法
public void attributeRemoved(ServletContextAttributeEvent event){
ServletContext application = event.getServletContext();
//获取被删除的属性名和属性值
String name = event.getName();
Object value = event.getValue();
System.out.println(application + "范围内名为" + name + "，值为" + value + "的属性被删除了!");
}
//当application范围的属性被替换时触发该方法
public void attributeReplaced(ServletContextAttributeEvent event){
ServletContext application = event.getServletContext();
//获取被替换的属性名和属性值
String name = event.getName();
Object value = event.getValue();
System.out.println(application + "范围内名为" + name + "，值为" + value + "的属性被替换了!");
}
}

2. 测试Servlet，Test.java

package test;
import java.io.IOException;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Test extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletContext sontext = getServletContext();
sontext.setAttribute("111", "aaa");
sontext.setAttribute("111", "bbb");
String t = (String)getServletContext().getAttribute("111");
System.out.println("AAAAA" + t);
getServletContext().removeAttribute("111");
}
}

3. web.xml中Listener和Servlet配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<listener>

<listener-class>test.MyServletContextAttributeListener</listener-class>
</listener>
<servlet>
<servlet-name>Test</servlet-name>
<servlet-class>test.Test</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Test</servlet-name>
<url-pattern>/Test</url-pattern>
</servlet-mapping>
</web-app>