过滤器-----用户登录验证过滤器(LoginFilter)

迈不过友情╰ 2022-04-14 04:41 267阅读 0赞

## 1.过滤器简介 ##

Java中的Filter 并不是一个标准的Servlet ，它不能处理用户请求，也不能对客户端生成响应。 主要用于对HttpServletRequest 进行预处理，也可以对HttpServletResponse 进行后处理，是个典型的处理链。

优点：过滤链的好处是，执行过程中任何时候都可以打断，只要不执行chain.doFilter()就不会再执行后面的过滤器和请求的内容。而在实际使用时，就要特别注意过滤链的执行顺序问题

## 2.登录过滤器Code案例 ##

1.  用户登录界面(**login.jsp**)

<%-- Created by IntelliJ IDEA. User: 网络黑寡妇 Date: 17-5-18 --%>
    <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
    <head>
        <title>登录界面</title>
    </head>
    <body>
    <div align="center">
    <form method="POST" name="frmLogin" action="LoginServlet">
        <h1 align="center">用户登录</h1><br/>
            <table border=1>
                <tr>
                    <td>用户名：</td>
                    <td>
                        <input type="text" name="username" value="Your name" size="20" maxlength="20" autocomplete="off" onfocus="if (this.value=='Your name') this.value='';"/>
                    </td>
                </tr>
                <tr>
                    <td>密  码：</td>
                    <td>
                        <input type="password" name="password" value="Your password" size="20" maxlength="20" autocomplete="off" onfocus="if (this.value=='Your password') this.value='';"/>
                    </td>
                </tr>
                <tr align="center">
                    <td colspan="4" height="40px">
                        <input type="submit" name="Submit" value="提 交" onClick="return validateLogin()"/>    
                        <input type="reset" name="Reset" value="重 置"/>
                    </td>
                </tr>
            </table>
    </form>
    </div>
    <script language="javascript"> function validateLogin() { var sUserName = document.frmLogin.username.value; var sPassword = document.frmLogin.password.value; if ((sUserName == "") || (sUserName == "Your name")) { alert("请输入用户名!"); return false; } if ((sPassword == "") || (sPassword == "Your password")) { alert("请输入密码!"); return false; } }

2.后台(Servlet)处理Code (**LoginServlet**)

package com.Servlet;
    
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    import java.io.IOException;
    
    /** * Created by dhc on 17-5-18. * user: 网络黑寡妇 */
    @WebServlet("/LoginServlet")
    public class LoginServlet extends HttpServlet{ 
        private static final long serialVersionUID = 1L;
    
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            HttpSession session = request.getSession();
            String adminName = request.getParameter("username");
            String adminpsw = request.getParameter("password");
    
            session.setAttribute("username", adminName); //存储在Session中
    
            if ( adminName.equals(admin) && adminpsw.equals(password))) {
            //main.jsp文件为要跳转的jsp界面.
              request.getRequestDispatcher("main.jsp").forward(request, response);
            } else {
              request.getRequestDispatcher("login.jsp").forward(request,response);
            }
        }

3.重点过滤器的编写 (LoginFilter)

package com.Filter;
    
    import javax.servlet.*;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.util.Arrays;
    import java.util.List;
    
    /** * Created by dhc on 17-5-18. * Description: 所有请求都走此过滤器来判断用户是否登录 * user: 网络黑寡妇 **/
    public class LoginFilter implements Filter{ 
        private String sessionKey;
        private String redirectUrl;
        private String uncheckedUrls;
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            ServletContext servletContext = filterConfig.getServletContext();
            //获取XML文件中配置参数
            sessionKey = servletContext.getInitParameter("userSessionKey");
            //System.out.println("sessionKey======" + sessionKey);//调试用
            redirectUrl = servletContext.getInitParameter("redirectPage");
           //System.out.println("redirectPage======" + redirectUrl);
            uncheckedUrls = servletContext.getInitParameter("uncheckedUrls");
            //System.out.println("uncheckedUrls=====" + uncheckedUrls);
        }
    
        @Override
        public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
            // 获得在下面代码中要用的request,response,session对象
            HttpServletRequest httpRequest = (HttpServletRequest) servletRequest;
            HttpServletResponse httpResponse = (HttpServletResponse) servletResponse;
            //1.获取请求URL
            String servletPath = httpRequest.getServletPath();    
    
            //2.检测1中获取的servletPath是否为不需要检测的URl中的一个.若是,放行
            List<String> urls = Arrays.asList(uncheckedUrls.split(","));
            if (urls.contains(servletPath)) {
                filterChain.doFilter(httpRequest, httpResponse);
                return;
            }
    
            //3.从session中获取SessionKey对应值,若值不存在,则重定向到redirectUrl
            Object user = httpRequest.getSession().getAttribute("username");
            if ((user == null)) {
               httpResponse.sendRedirect(httpRequest.getContextPath() + redirectUrl);            
               return;
            }
    
            //4.若存在,则放行
            filterChain.doFilter(httpRequest, httpResponse);
        }
    
        @Override
        public void destroy() {
        }
    }

4.配置 **web.XML** 文件

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1">        
    
        
        
        <context-param>
            <param-name>userSessionKey</param-name>
            <param-value>username</param-value>
        </context-param>
        
        <context-param>
            <param-name>redirectPage</param-name>
            <param-value>/login.jsp</param-value>
        </context-param>
        
        <context-param>
            <param-name>uncheckedUrls</param-name>
            <param-value>/index.jsp,/LoginServlet</param-value>
        </context-param>
    
        <filter>
            <filter-name>LoginFilter</filter-name>
            <filter-class>com.Filter.LoginFilter</filter-class>
        </filter>
        <filter-mapping>
            <filter-name>LoginFilter</filter-name>
            
            <url-pattern>/*</url-pattern>
        </filter-mapping>
    </web-app>