写Filter一定要知道该Filter过滤哪个或哪些资源，不是所有的Filter都过滤/*的资源。

logn.jsp

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
  <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
    <form action="/day19/LoginServlet" method="post">
        <table border="1" align="center">
            <caption><br>用户自动登录</caption>
            <tr>
                <th>用户名</th>
                <td><input type="text" name="username"/></td>
            </tr>
            <tr>
                <th>密码</th>
                <td><input type="password" name="password"/></td>
            </tr>
            <tr>
                <th>时间</th>
                <td>
                    <input checked name="time" type="radio" value="60"/>1分钟
                    <input name="time" type="radio" value="180"/>3分钟
                    <input name="time" type="radio" value="300"/>5分钟
                </td>
            </tr>
            <tr>
                <td colspan="2" align="center">
                    <input type="submit" value="提交"/>
                </td>
            </tr>
        </table>
    </form>
  </body>
</html>

login.jsp

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
  <meta http-equiv="content-type" content="text/html; charset=UTF-8">
  </head>
  <body>
    <form action="/day19/LoginServlet" method="post">
        <table border="1" align="center">
            <caption><br>用户自动登录</caption>
            <tr>
                <th>用户名</th>
                <td><input type="text" name="username"/></td>
            </tr>
            <tr>
                <th>密码</th>
                <td><input type="password" name="password"/></td>
            </tr>
            <tr>
                <th>时间</th>
                <td>
             <input checked name="time" type="radio" value="60"/>1分钟
                    <input name="time" type="radio" value="180"/>3分钟
                    <input name="time" type="radio" value="300"/>5分
                </td>
            </tr>
            <tr>
                <td colspan="2" align="center">
                    <input type="submit" value="提交"/>
                </td>
            </tr>
        </table>
    </form>
  </body>
</html>

welcome.jsp

<%@ page language="java" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <body>

    <%-- 
    用户名->Filter->welcome.jsp
    --%>

    欢迎${!empty sessionScope.username?username:'游客'}光临
  </body>
</html>

autoLoginFilter(过滤器)


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.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//对敏感页面或目录进行认证
public class AutoLoginFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    public void doFilter(ServletRequest req, ServletResponse res,FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        //取得浏览器的Cookie
        Cookie[] cookies = request.getCookies();
         //记录cookie值
        Cookie userCookie = null;
        if(cookies!=null){
            for(Cookie c : cookies){
                if(c.getName().equals("usernameAndPassword")){
                    userCookie = c;
                    break;
                }
            }
            //找到对应的Cookie
            if(userCookie!=null){
                String usernameAndPassword = userCookie.getValue();
                String[] both = usernameAndPassword.split("_");
                String username = both[0];
                String password = both[1];
                if(username.equals("jack") && password.equals("123")){
                    request.getSession().setAttribute("username",username);
                }
            }
        }
        //发行资源
        chain.doFilter(request,response);
    }   

    public void destroy() {
    }
}

LoginServlet

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//用户自动登录
public class LoginServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        if(username!=null && password!=null && username.trim().length()>0 && password.trim().length()>0){
            if(username.equals("jack") && password.equals("123")){
                //登录成功，将信息绑定到HttpSession域对象中
                request.getSession().setAttribute("username",username);
                request.getSession().setAttribute("password",password);
                //向浏览器写入Cookie
                Cookie cookie = new Cookie("usernameAndPassword",username+"_"+password);
                int time = Integer.parseInt(request.getParameter("time"));
                cookie.setMaxAge(time);
                response.addCookie(cookie);
                //重定向到welcome.jsp页面
                response.sendRedirect(request.getContextPath()+"/welcome.jsp");
            }
        }
    }
}

web.xml

<filter>
    <filter-name>AutoLoginFilter</filter-name>
    <filter-class>cn.itcast.web.filter.AutoLoginFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>AutoLoginFilter</filter-name>
    <url-pattern>/welcome.jsp</url-pattern>
  </filter-mapping>

Filter案例用户自动登录学习笔记

logn.jsp

login.jsp

welcome.jsp

autoLoginFilter(过滤器)

LoginServlet

web.xml

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