过滤器-----用户登录验证过滤器(LoginFilter)

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

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; } }

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>