Java Web过滤器详解

时间：2021-05-20

过滤器是什么玩意？

所谓过滤器，其实就是一个服务端组件，用来截取用户端的请求与响应信息。

过滤器的应用场景：
1.对用户请求进行统一认证，保证不会出现用户账户安全性问题

2.编码转换，可在服务端的过滤器中设置统一的编码格式，避免出现乱码

3.对用户发送的数据进行过滤替换

4.转换图像格式

5.对响应的内容进行压缩

其中，第1,2场景经常涉及。

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP 'login.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page">  </head> <body> <form action="<%=path %>/servlet/LoginServlet" method="post" > 用户名:<input type="text" name="username" /> 密码:<input type="password" name="password" /> <input type="submit" value="登录" /> </form> </body></html>

success.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8" contentType="text/html; charset=utf-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP 'index.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page">  </head> <body> </body></html>

failure.jsp

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP 'login.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page">  </head> <body> 登录失败，请检查用户名或密码！ </body></html>

LoginFilter.java

package com.cityhuntshou.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;import javax.servlet.http.HttpSession;public class LoginFilter implements Filter { private FilterConfig config; public void destroy() { } public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) arg0; HttpServletResponse response = (HttpServletResponse) arg1; HttpSession session = request.getSession(); //过滤器实际应用场景之二-----编码转换 String charset = config.getInitParameter("charset"); if(charset == null) { charset = "UTF-8"; } request.setCharacterEncoding(charset); String noLoginPaths = config.getInitParameter("noLoginPaths"); if(noLoginPaths != null) { String[] strArray = noLoginPaths.split(";"); for(int i = 0; i < strArray.length; i++) { //空元素，放行 if(strArray[i] == null || "".equals(strArray[i])) continue; if(request.getRequestURI().indexOf(strArray[i]) != -1) { arg2.doFilter(arg0, arg1); return; } } } if(request.getRequestURI().indexOf("login.jsp") != -1 || request.getRequestURI().indexOf("LoginServlet") != -1) { arg2.doFilter(arg0, arg1); return; } if(session.getAttribute("username") != null) { arg2.doFilter(arg0, arg1); } else { response.sendRedirect("login.jsp"); } } public void init(FilterConfig arg0) throws ServletException { config = arg0; }}

LoginServlet.java

package com.cityhuntshou.servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class LoginServlet extends HttpServlet { /** * Constructor of the object. */ public LoginServlet() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } /** * The doGet method of the servlet. <br> * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } /** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); String password = request.getParameter("password"); //new String(username.getBytes("ISO-8859-1"),"UTF-8") System.out.println(username); if("admin".equals(username) && "admin".equals(password)) { //校验通过 HttpSession session = request.getSession(); session.setAttribute("username", username); response.sendRedirect(request.getContextPath()+"/success.jsp"); } else { //校验失败 response.sendRedirect(request.getContextPath()+"/failure.jsp"); } } /** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */ public void init() throws ServletException { // Put your code here }}

web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://.cityhuntshou.filter.LoginFilter</filter-class> <init-param> <param-name>noLoginPaths</param-name> <param-value>login.jsp;failure.jsp;loginServlet</param-value> </init-param> <init-param> <param-name>charset</param-name> <param-value>UTF-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>LoginFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping></web-app>

运行效果：

访问结果：

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Java Web过滤器详解

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