过滤器篇(1)-----用户登录验证过滤器(LoginFilter)

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1. 过滤器简介

用过滤器实现登录和访问权限.

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

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&nbsp;&nbsp;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()"/> &nbsp;&nbsp;&nbsp;                    <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;        }    }</script></body></html>

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">            <!--检测用户是否登录的过滤器配置-->    <!--用户信息存放到session中的键的名字-->    <context-param>        <param-name>userSessionKey</param-name>        <param-value>username</param-value>    </context-param>    <!--若未登录，需要重定向的页面-->    <context-param>        <param-name>redirectPage</param-name>        <param-value>/login.jsp</param-value>    </context-param>    <!--不需要拦截的URL列表;注意配置时不要拦截后台对用户和密码判断的页面,否则可能登录登录不进主界面-->    <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>        <!--过滤站点下所有文件,也可设置成过滤某一类文件如:  "*.jsp" 或是过滤掉某一个文件夹下的所有文件,如: "/目录名/*" -->        <url-pattern>/*</url-pattern>    </filter-mapping></web-app>

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