Java Web过滤器详解

2019-11-26 11:33:41

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来源：转载

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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">  <!--  <link rel="stylesheet" type="text/css" href="styles.css">  --> </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">  <!--  <link rel="stylesheet" type="text/css" href="styles.css">  --> </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">  <!--  <link rel="stylesheet" type="text/css" href="styles.css">  --> </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://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"> <display-name></display-name> <servlet>  <description>This is the description of my J2EE component</description>  <display-name>This is the display name of my J2EE component</display-name>  <servlet-name>LoginServlet</servlet-name>  <servlet-class>com.cityhuntshou.servlet.LoginServlet</servlet-class> </servlet> <servlet-mapping>  <servlet-name>LoginServlet</servlet-name>  <url-pattern>/servlet/LoginServlet</url-pattern> </servlet-mapping>   <welcome-file-list>  <welcome-file>index.jsp</welcome-file> </welcome-file-list>  <filter>    <filter-name>LoginFilter</filter-name>    <filter-class>com.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：