Java中的過濾器和監聽器

時間  2019-12-04
標籤 java 過濾器 監聽器 欄目 Java 简体版
原文   原文鏈接

過濾器

一個過濾器能夠附加到一個或者多個Servlet上，一個Servlet能夠附加一個或者多個Filter。一個過濾器必須實現javax.servlet.Filter接口並實現其中的三個方法。html

  • init()方法：java

    這個方法在實例化過濾器時被調用，主要用於使過濾器爲處理作準備。容器爲這個方法傳遞一個FilterConfig對象，其中包含配置信息。web

  • doFilter()：bash

    這個方法用於處理請求和相應。它接受3個輸入參數：ServletRequest、ServletReponse、FilterChain對象。FilterChain對於正確的過濾操做相當重要。doFilter()方法必須調用FilterChain的doFilter()方法，除非該方法用來攔截之後的下游處理session

  • destroy()：app

    該方法由容器在銷燬過濾器實例以前調用。jsp

    package com.tz.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class EncodingFilter implements Filter{
	String encoding = null;
	FilterConfig config = null;
	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		this.config=null;
		this.encoding=null;
	}
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		if(encoding!=null){
			//對請求進行編碼設置
			request.setCharacterEncoding(encoding);
		}
		chain.doFilter(request, response);
	}
	@Override
	public void init(FilterConfig config) throws ServletException {
		// TODO Auto-generated method stub
		this.config = config;
		this.encoding = config.getInitParameter("encoding");
	}
	
}
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    web.xml配置：ide

    <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
		 xmlns="http://java.sun.com/xml/ns/javaee" 
		 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
		 					 id="WebApp_ID" version="3.0">
  <display-name>test</display-name>
  <filter>
  	<filter-name>encodingFilter</filter-name>
  	<filter-class>com.tz.filter.EncodingFilter</filter-class>
  	<init-param>
  		<param-name>encoding</param-name>
  		<param-value>utf-8</param-value>
  	</init-param>
  </filter>
  <filter-mapping>
  	<filter-name>encodingFilter</filter-name>
  	<url-pattern>/*</url-pattern>
  </filter-mapping>
  
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>
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    Jsp文件：post

    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML>
<html>
  <head>
    <title>編碼過濾器測試</title>
	<meta http-equiv="content-type" content="text/html;charset=utf-8">
  </head>
  
  <body>
    <form action="process.jsp" name="form1" method="post">
    	姓名：<input type="text" name="userName" />
    	<input type="submit" value="提交" name="submit">
    </form>
  </body>
</html>
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    process.jsp：測試

    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML>
<html>
  <head>
    <title>編碼過濾器測試</title>
	<meta http-equiv="content-type" content="text/html;charset=utf-8">
  </head>
  
  <body>
    <p><%=request.getParameter("userName") %>,你好！</p>
    <%=request.getCharacterEncoding() %>
  </body>
</html>
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監聽器

在定義監聽器類時，只須要實現相應的監聽器接口便可。如實現了 ServletContextListener 和ServletContextAttributeListener的類就能夠監聽到ServletContext對象的生命週期變化狀況和ServletContext對象中屬性的變化狀況。實現了HttpSessionListener和HttpServletAttributeListener接口的類就能夠監聽到HttpSession對象的生命週期變化和HttpSession對象中的屬性變化。

package com.tz.listener;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class ContextListenerTest implements ServletContextListener,ServletContextAttributeListener{

	//當應用被移除到容器時觸發
	@Override
	public void contextDestroyed(ServletContextEvent arg0) {
		System.out.println("監聽到應用被移除。。。。。。");
	}

	//當應用在容器中啓動時觸發
	@Override
	public void contextInitialized(ServletContextEvent arg0) {
		System.out.println("監聽到應用被啓動。。。。。。");
	}

	//ServletContext中新增屬性時執行此方法
	@Override
	public void attributeAdded(ServletContextAttributeEvent event) {
		System.out.println("監聽到新增了一個叫"+event.getName()+"的屬性！");
	}

	@Override
	public void attributeRemoved(ServletContextAttributeEvent arg0) {
		System.out.println("removed......");
	}

	@Override
	public void attributeReplaced(ServletContextAttributeEvent arg0) {
		System.out.println("replaced......");
	}

}
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package com.tz.listener;

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class SessionListenerTest implements HttpSessionListener,HttpSessionAttributeListener{
	
	//在線人數統計
	int count = 0;
	
	//當產生一個新的HttpSession對象時(新用戶上線)執行此方法
	@Override
	public void sessionCreated(HttpSessionEvent event) {
		event.getSession().getServletContext().setAttribute("count",++count);
		System.out.println("監聽到新用戶"+event.getSession().getId()+"上線了！");
	}
	
	//當一個HttpSession銷燬(用戶下線)時執行此方法
	@Override
	public void sessionDestroyed(HttpSessionEvent event) {
		event.getSession().getServletContext().setAttribute("count",--count);
		System.out.println("監聽到新用戶"+event.getSession().getId()+"下線了！");
	}
	
	@Override
	public void attributeAdded(HttpSessionBindingEvent event) {
		System.out.println("監聽到"+ event.getName()+"屬性新增了,屬性值是"+event.getValue());
	}

	@Override
	public void attributeRemoved(HttpSessionBindingEvent event) {
		// TODO Auto-generated method stub
		System.out.println("監聽到"+ event.getName()+"屬性被刪除了");
		
	}

	@Override
	public void attributeReplaced(HttpSessionBindingEvent event) {
		// TODO Auto-generated method stub
		System.out.println("監聽到"+ event.getName()+"屬性被修改了");
		
	}
	

}
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web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
		 xmlns="http://java.sun.com/xml/ns/javaee" 
		 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
		 					 id="WebApp_ID" version="3.0">
  <display-name>test</display-name>
  
  <listener>
  	<listener-class>com.tz.listener.ContextListenerTest</listener-class>
  </listener>
  
  <listener>
  	<listener-class>com.tz.listener.SessionListenerTest</listener-class>
  </listener>
  
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>
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jsp:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML>
<html>
  <head>
    <title>編碼過濾器測試</title>
	<meta http-equiv="content-type" content="text/html;charset=utf-8">
  </head>
  
  <body>
    
    <h2>Listener應用實例測試</h2>
    <%
    	application.setAttribute("admin", "liubin");
    	application.setAttribute("admin", "xiaohuang");
    	application.removeAttribute("admin");
    	session.setAttribute("now", new Date());
    	session.setAttribute("now", "2016-05-09");
    	session.removeAttribute("now");
     %>
            目前在線人數：<%=application.getAttribute("count") %>人！
     <a href="logout.jsp" style="list-style: none">註銷</a>
  </body>
</html>
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logout.jsp:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML>
<html>
  <head>
    <title>Listener應用實例</title>
	<meta http-equiv="content-type" content="utf-8">
  </head>
  
  <body>
  	<h2>Listener應用實例</h2>
    <%
    	//銷燬session對象
    	session.invalidate();
     %>
     	恭喜你註銷成功！目前在線人數：<%=application.getAttribute("count") %>
  </body>
</html>
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