JavaWeb核心技术系列教程(17)——Filter_小言_互联网的博客

JavaWeb核心技术系列教程(17)——Filter

2020-04-01 15:16 320人阅读评论(0)

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版权声明

本文原创作者：谷哥的小弟
作者博客地址：http://blog.csdn.net/lfdfhl

Filter概述

Filter也称之为过滤器，它是JavaWeb三大组件(Servlet、Filter、Listener)之一。它主要用于对用户请求进行预处理和对响应结果进行后处理。也就是说：使用Filter技术可在HttpServletRequest到达Web资源之前拦截客户的HttpServletRequest并根据需要检查HttpServletRequest，亦可修改HttpServletRequest；使用Filter技术可在HttpServletResponse到达客户端之前拦截HttpServletResponse并根据需要检查HttpServletResponse，亦可修改HttpServletResponse；图示如下：

Filter接口常用方法

Servlet API中提供了javax.servlet.Filter接口用于实现过滤器Filter。在此，介绍Filter接口中常用的方法及其作用。

public void init(FilterConfig filterConfig) throws ServletException

该方法用来初始化过滤器。

public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException

该方法用于处理过滤。其中，参数request和response为Web服务器或Filter链中的上一个Filter传递过来的请求和响应对象；参数chain代表当前Filter链的对象。

public void destroy( )

该方法用于释放被Filter对象打开的资源；例如：关闭数据库和IO流

小结
init( )方法和destroy( )方法仅会被调用一次；而doFilter( )方法可能会被多次调用。

Filter入门示例

在此，我们通过示例的方式入门Filter

项目结构

index.html

index.html代码如下：

<!DOCTYPE html>
<!-- 本文作者：谷哥的小弟-->
<!-- 博客地址：https://blog.csdn.net/lfdfhl-->
<html>
	<head>
		<meta charset="utf-8">
		<title>index</title>
	</head>
	<body>
	    <h2 align="center" style="color: red;">本文作者：谷哥的小弟</h2>
		<h2 align="center" style="color: red;">博客地址：http://blog.csdn.net/lfdfhl</h2>
	</body>
</html>

index.html页面如下：

MyServlet

package cn.com.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 */
public class MyServlet extends HttpServlet {
	
	private static final long serialVersionUID = 638101330297540752L;

	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		System.out.println("Servlet doGet( )");
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		System.out.println("Servlet doPost( )");
	}
}

FilterImpl

package cn.com.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;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 * 
 * Filter入门示例
 */
public class FilterImpl implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		System.out.println("Filter init( )");
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
		System.out.println("Filter doFilter( ) before");
		//chain.doFilter(request, response);
		chain.doFilter(request, response);
		System.out.println("Filter doFilter( ) after");
	}

	@Override
	public void destroy() {
		System.out.println("Filter destroy( )");
	}

}

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>Filter01</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <!-- 配置servlet -->
  
  <!-- 注册servlet -->
  <servlet>
    <servlet-name>myServlet</servlet-name>
    <servlet-class>cn.com.servlet.MyServlet</servlet-class>
  </servlet>
  <!-- 映射servlet -->
  <servlet-mapping>
      <servlet-name>myServlet</servlet-name>
      <url-pattern>/myServlet</url-pattern>
  </servlet-mapping>
  
  <!-- 配置filter -->
  
  <!-- 注册filter -->
  <filter>
    <filter-name>filterImpl</filter-name>
    <filter-class>cn.com.filter.FilterImpl</filter-class>
  </filter>
  <!-- 映射filter -->
  <filter-mapping>
    <filter-name>filterImpl</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  
</web-app>

请注意：类似于与Servlet，我们需要在配置文件web.xml中配置过滤器filter。

访问index.hmtl

访问地址：http://localhost:8080/Filter01/index.html

访问MyServlet

访问地址：http://localhost:8080/Filter01/myServlet

示例小结

对于客户端请求而言：请求先到达拦截器再到达服务端Web资源
对于服务器响应而言：响应先到达拦截器再到达客户端的浏览器

Filter映射

当在Web应用中开发Filter之后需要在web.xml中对其进行注册和配置；其中，在配置时使用< filter-mapping >标签。在此，对于Filter的注册，不再过多强调；我们来一起看看两种常见的Filter的映射。

url-pattern

在< filter-mapping >标签中可使用子标签< url-pattern >设置拦截路径；常用的为/*表示拦截所有请求。

dispatcher

在< filter-mapping >标签中可使用子标签< dispatcher >用于设置依据访问资源的方式进行拦截。< dispatcher >子标签常用取值如下：

1、REQUEST
目标资源被直接访问或者系统重定向后指向该目标资源时Filter才拦截。这也是默认的值

2、FORWARD
目标资源通过RequestDispatcher.forward(request, response)被调用时Filter才拦截

3、ERROR
目标资源是在系统处理异常时被调用

4、INCLUDE
目标资源通过RequestDispatcher.include(request, response)被调用时Filter才拦截

Filter链

在Web应用程序中可以注册多个Filter程序，每个Filter程序都可针对某具体URL进行拦截。如果多个Filter程序对同一个URL进行拦截，那么这些Filter就会串联成为Filter链(FilterChain滤器链)。Filter链用FilterChain对象来表示，其中的doFilter( )方法表示让Filter链上的当前过滤器放行，使得请求进入下一 Filter，图示如下：

Web服务器根据各Filter在web.xml文件中的注册顺序，依次调用各Filter。在此，以示例形式介绍Filter链的使用。

项目结构

index.html

index.html代码如下：

<!DOCTYPE html>
<!-- 本文作者：谷哥的小弟-->
<!-- 博客地址：https://blog.csdn.net/lfdfhl-->
<html>
	<head>
		<meta charset="utf-8">
		<title>index</title>
	</head>
	<body>
	    <h2 align="center" style="color: red;">本文作者：谷哥的小弟</h2>
		<h2 align="center" style="color: red;">博客地址：http://blog.csdn.net/lfdfhl</h2>
	</body>
</html>

index.html页面如下：

MyServlet

package cn.com.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 */
public class MyServlet extends HttpServlet {
	
	private static final long serialVersionUID = 638101330297540752L;

	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		System.out.println("Servlet doGet( )");
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		System.out.println("Servlet doPost( )");
	};
}

FilterImpl1

package cn.com.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;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 */
public class FilterImpl1 implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
		System.out.println("Filter1 doFilter( ) before");
		//放行
		chain.doFilter(request, response);
		System.out.println("Filter1 doFilter( ) after");
	}

	@Override
	public void destroy() {
		
	}

}

FilterImpl2

package cn.com.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;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 */
public class FilterImpl2 implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
		System.out.println("Filter2 doFilter( ) before");
		//放行
		chain.doFilter(request, response);
		System.out.println("Filter2 doFilter( ) after");
	}

	@Override
	public void destroy() {
		
	}

}

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>Filter02</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <!-- 配置Servlet -->
  <servlet>
    <servlet-name>myServlet</servlet-name>
    <servlet-class>cn.com.servlet.MyServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>myServlet</servlet-name>
      <url-pattern>/myServlet</url-pattern>
  </servlet-mapping>
  
  <!-- 配置第一个filter -->
  <filter>
    <filter-name>filterImpl1</filter-name>
    <filter-class>cn.com.filter.FilterImpl1</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>filterImpl1</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  
  <!-- 配置第二个filter -->
   <filter>
    <filter-name>filterImpl2</filter-name>
    <filter-class>cn.com.filter.FilterImpl2</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>filterImpl2</filter-name>
    <url-pattern>/myServlet</url-pattern>
  </filter-mapping>
</web-app>

测试

请求路径：http://localhost:8080/Filter02/myServlet

FilterConfig接口

javax.servlet.FilterConfig接口封装了web.xml配置文件中filter标签下init-param子标签的配置信息。在此，介绍FilterConfig接口中的常用方法及其作用。

public String getFilterName( )

该方法用于获取Filter名字。

public ServletContext getServletContext( )

该方法用于获取ServletContext。

public String getInitParameter(String name)

该方法用于依据初始化参数名称获取其对应的值。

public Enumeration< String > getInitParameterNames( )

该方法用于获取所有初始化参数的名称。

在此，以示例形式介绍FilterConfig的使用。

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>Filter06</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <!-- 配置servlet -->
  
  <!-- 注册servlet -->
  <servlet>
    <servlet-name>myServlet</servlet-name>
    <servlet-class>cn.com.servlet.MyServlet</servlet-class>
  </servlet>
  <!-- 映射servlet -->
  <servlet-mapping>
      <servlet-name>myServlet</servlet-name>
      <url-pattern>/myServlet</url-pattern>
  </servlet-mapping>
  
  <!-- 配置filter -->
  
  <!-- 注册filter -->
  <filter>
    <filter-name>filterImpl</filter-name>
    <filter-class>cn.com.filter.FilterImpl</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <!-- 映射filter -->
  <filter-mapping>
    <filter-name>filterImpl</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  
</web-app>

FilterImpl

package cn.com.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;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 * 
 * FilterConfig使用示例
 */
public class FilterImpl implements Filter {
	private FilterConfig mFilterConfig;
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		System.out.println("Filter init( )");
		mFilterConfig=filterConfig;
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
		System.out.println("Filter doFilter( ) before");
		String initParameter = mFilterConfig.getInitParameter("encoding");
		System.out.println("initParameter="+initParameter);
		chain.doFilter(request, response);
		System.out.println("Filter doFilter( ) after");
	}

	@Override
	public void destroy() {
		System.out.println("Filter destroy( )");
	}

}

Filter应用示例

在此，以示例形式介绍Filter常见应用场景及其技术特点。

利用Filter实现粗粒度权限控制

实现方式概述

利用PrivilegeFilter拦截用户对于index.html页面的访问
在PrivilegeFilter中判断用户是否已经登录；假若已登录则放行，否则跳转至login.html
LoginServlet处理登录逻辑

项目结构

index.html

<!DOCTYPE html>
<!-- 本文作者：谷哥的小弟-->
<!-- 博客地址：https://blog.csdn.net/lfdfhl-->
<html>
	<head>
		<meta charset="UTF-8">
		<title>index</title>
	</head>
	<body>
		<h2 align="left" style="color: red;">本文作者：谷哥的小弟</h2>
		<h2 align="left" style="color: red;">博客地址：http://blog.csdn.net/lfdfhl</h2>
		<h1>This is index page</h1>
		<h1>您已登录 , 欢迎来访</h1>
	</body>
</html>

login.html

<!DOCTYPE html>
<!-- 本文作者：谷哥的小弟-->
<!-- 博客地址：https://blog.csdn.net/lfdfhl-->
<html>
	<head>
		<meta charset="UTF-8">
		<title>login</title>
	</head>
	<body>
		<form action="/Filter03/LoginServlet" method="post">
			账 户：<input type="text" name="username"/><br/><br/>
			密 码：<input type="password" name="password"/><br/><br/>
			<input type="submit" value="提交">
		</form>
	</body>
</html>

PrivilegeFilter

package cn.com.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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 * 
 * 利用Filter实现粗粒度的权限控制
 * 
 * 过滤欲访问index.html的请求
 * 1 若已经登陆则放行
 * 2 若没有登录则跳转至login.html
 */
public class PrivilegeFilter implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {

	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
		HttpServletRequest httpServletRequest=(HttpServletRequest) request;
		HttpSession session = httpServletRequest.getSession();
		String username=(String) session.getAttribute("username");
		if(username!=null) {
			//如果用户名不为空则放行
			chain.doFilter(request, response);
		} else {
			//如果用户名为空则跳转至登录页面
			httpServletRequest.getRequestDispatcher("/login.html").forward(request, response);
		}
		
	}

	@Override
	public void destroy() {
		
	}

}

LoginServlet

package cn.com.servlet;

import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 */
public class LoginServlet extends HttpServlet {
	
	private static final long serialVersionUID = -1498309426781988290L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doPost(request, response);
	}
	
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String username=request.getParameter("username");
		if(username!=null&&username.length()>=0) {
			HttpSession session=request.getSession();
			Cookie cookie = new Cookie("JSESSIONID", session.getId());
			cookie.setMaxAge(60 * 30);
			cookie.setPath(request.getContextPath());
			response.addCookie(cookie);
			//保存数据至Session中
			request.getSession().setAttribute("username", username);
			//转发至index.html
			RequestDispatcher requestDispatcher = request.getRequestDispatcher("/index.html");
			requestDispatcher.forward(request, response);
		}else {
			//转发至login.html
			RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.html");
			requestDispatcher.forward(request, response);
		}
	}
}

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>Filter03</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>cn.com.servlet.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/LoginServlet</url-pattern>
  </servlet-mapping>
  
  <!-- 拦截访问index.html的请求 -->
  <filter>
    <filter-name>PrivilegeFilter</filter-name>
    <filter-class>cn.com.filter.PrivilegeFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>PrivilegeFilter</filter-name>
    <url-pattern>/index.html</url-pattern>
  </filter-mapping>
  
  
</web-app>

利用Filter解决全站编码问题

实现方式概述

利用EncodingFilter统一处理GET和POST的请求及其响应。

项目结构

index.html

<!DOCTYPE html>
<!-- 本文作者：谷哥的小弟-->
<!-- 博客地址：https://blog.csdn.net/lfdfhl-->
<html>
	<head>
		<meta charset="UTF-8">
		<title>Index</title>
	</head>
	<body>
		<h3 align="left" style="color: red;">本文作者：谷哥的小弟</h3>
		<h3 align="left" style="color: red;">博客地址：http://blog.csdn.net/lfdfhl</h3>

		<h5>以下为GET方式提交数据至服务器</h5>
		<a href="/Filter04/LoginServlet?username=张三&password=123456">提交</a>
		<br /><br />
		<h5>以下为POST方式提交数据至服务器</h5>
		<form action="/Filter04/LoginServlet" method="post">
			用户：<input type="text" name="username" /><br /><br />
			密码：<input type="password" name="password" /><br /><br />
			<input type="submit" value="提交" />
		</form>
	</body>
</html>

LoginServlet

package cn.com.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 *
 */
public class LoginServlet extends HttpServlet {
	
	private static final long serialVersionUID = 8831676289832788100L;

	public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		doPost(request, response);
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		String username = request.getParameter("username");
		response.getWriter().println(username);
	}
	
	
}

EncodingFilter

package cn.com.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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 本文作者：谷哥的小弟 
 * 博客地址：http://blog.csdn.net/lfdfhl
 *
 */
public class EncodingFilter implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {

	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)throws IOException, ServletException {
		//将ServletRequest强转为HttpServletRequest
		HttpServletRequest httpServletRequest = (HttpServletRequest) request;
		//将ServletResponse强转为HttpServletResponse
		HttpServletResponse httpServletResponse=(HttpServletResponse) response;
		//获取请求方式
		String method = httpServletRequest.getMethod();
		System.out.println("method="+method);
		//设置响应内容的编码方式
		httpServletResponse.setContentType("text/html;charset=utf-8");
		//设置POST请求时HttpServletRequest的编码方式
		httpServletRequest.setCharacterEncoding("utf-8");
		//放行
		chain.doFilter(httpServletRequest, httpServletResponse);
	}

	@Override
	public void destroy() {

	}
}

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>Filter04</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>cn.com.servlet.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
     <servlet-name>LoginServlet</servlet-name>
     <url-pattern>/LoginServlet</url-pattern>
  </servlet-mapping>
  
  <!-- 配置编码过滤器 -->
  <filter>
     <filter-name>EncodingFilter</filter-name>
     <filter-class>cn.com.filter.EncodingFilter</filter-class>
  </filter>
  <filter-mapping>
     <filter-name>EncodingFilter</filter-name>
     <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

转载：https://blog.csdn.net/lfdfhl/article/details/101977118

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