cookie为用户登陆服务器后，服务器写在客户端的文件。

我们在登录126邮箱时，如果勾选上两周内自动登录，两周内不用输入用户名和密码邮箱会自动登录，这是因为第一次登录时服务器将用户名和密码写入cookie中，并返回给客户端。

下次登录时Http协议会带着用户的cookie去服务器验证，因为服务器已经存储用户的信息，所以会自动登录。

登录代码：

package com.dr.course;

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;  

public class LoginServlet extends HttpServlet {  

    public void doGet(HttpServletRequest request, HttpServletResponse response)  

            throws ServletException, IOException {  

        this.doPost(request, response);  

    }  

    public void doPost(HttpServletRequest request, HttpServletResponse response)  

            throws ServletException, IOException {  

           String username=request.getParameter("username");  

           String password=request.getParameter("password");  

           String savetime=request.getParameter("saveTime");  

           if(CheckLogin.login(username, password)){  

               if(null!=savetime){  

                   int saveTime=Integer.parseInt(savetime);//这里接受的表单值为天来计算的  

                   int seconds=saveTime*24*60*60;  

                   Cookie cookie = new Cookie("user", username+"=="+password);  

                   cookie.setMaxAge(seconds);                     

                   response.addCookie(cookie);  

               }  

               request.setAttribute("username",username);  

               request.getRequestDispatcher("/main126.jsp").forward(request,response);  

           }else{  

               request.getRequestDispatcher("/failure.jsp").forward(request,response);  

           }  

    }  

}  

验证代码：

package com.dr.course;

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;  

public class IndexFilter implements Filter {  

    public void destroy() {  

        // TODO Auto-generated method stub  

    }  

    public void doFilter(ServletRequest arg0, ServletResponse arg1,  

            FilterChain arg2) throws IOException, ServletException {

          

           System.out.println("every request pass here haha");

        HttpServletRequest request = (HttpServletRequest) arg0;  

        HttpServletResponse response = (HttpServletResponse) arg1;  

        Cookie[] cookies = request.getCookies();  

        String[] cooks = null;  

        String username = null;  

        String password = null;  

        if (cookies != null) {  

            for (Cookie coo : cookies) {  

                String aa = coo.getValue();  

                cooks = aa.split("==");  

                if (cooks.length == 2) {  

                    username = cooks[0];  

                    password = cooks[1];  

                }  

            }  

        }

        System.out.println("cookie username | " + username);

        System.out.println("cookie password | " + password);

        if (CheckLogin.login(username, password)) {

               System.err.println("check successfully cookie data ");

            request.getSession().setAttribute("username",username);  

            request.getRequestDispatcher("/main126.jsp").forward(request, response);

        }else{  

            arg2.doFilter(request,response );  

        }  

    }  

    public void init(FilterConfig arg0) throws ServletException {  

        // TODO Auto-generated method stub  

    }  

}

package com.dr.course;

public class CheckLogin {

        public static boolean login(String username, String password) {  

               if ("admin".equals(username) && "123456".equals(password)) {  

                   return true;  

               } else {  

                   return false;  

               }  

           }  

}

web.xml中配置如下：

- <filter>

 <filter-name>loginFilter</filter-name>

 <filter-class>com.dr.course.IndexFilter</filter-class>

 </filter>

- <filter-mapping>

 <filter-name>loginFilter</filter-name>

 <url-pattern>/main126.jsp</url-pattern>

 </filter-mapping>

- <servlet>

 <servlet-name>LoginServlet</servlet-name>

 <servlet-class>com.dr.course.LoginServlet</servlet-class>

 </servlet>

- <servlet-mapping>

 <servlet-name>LoginServlet</servlet-name>

 <url-pattern>/login.do</url-pattern>

 </servlet-mapping>

将目录加入到Tomcat中，开启Tomcat，打开浏览器输入网址:http://127.0.0.1:8080/AutoLogin/login.do进行测试。