使用Cookie实现自动登录

喜欢ヅ旅行 2022-06-07 10:15 235阅读 0赞

\#说明  
      在之前的博文[《了解Cookie和Session》][Cookie_Session]中，我们初步认识了Cookie和Session。在之后的学习中，了解了Cookie的使用场景：A. sessionid的存储 B.购物车 C.自动登录。本文对使用Cookie实现自动登录的原理和代码实现进行阐述。

\#正文  
\#\#实现原理  
**Cookie如何保存信息？**  
      A cookie has a name, a single value, and optional attributes such as a comment, path and domain qualifiers, a maximum age, and a version number.*（摘自Servlet文档）*

cookie是 < key,value >结构，它的value值只能存储String类型

当用户通过浏览器**第一次访问服务器**时，服务器向浏览器**添加cookie信息**，cookie中保存了用户的用户名和密码，当用户再次通过**同一浏览器**访问该浏览器时，服务器会进行自动登录校验，发现cookie中的用户信息，实现自动登录。

**cookie的传递**  
      The servlet sends cookies to the browser by using the HttpServletResponse.addCookie(javax.servlet.http.Cookie) method, which adds fields to HTTP response headers to send cookies to the browser, one at a time.  
      The browser returns cookies to the servlet by adding fields to HTTP request headers. Cookies can be retrieved from a request by using the HttpServletRequest.getCookies() method.

servelt通过HttpServletResponse.addCookie()方法将cookie添加到HTTP响应头的字段中，发送到浏览器。浏览器请求服务器时，在HTTP请求头中添加字段cookie,在服务器使用HttpServletRequest.getCookies()获取cookies

![这里写图片描述][SouthEast]

\#\#代码实现  
**LoginServlet**

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		
    		String uname = request.getParameter("uname");
    		String pwd = request.getParameter("pwd");
    		UserBiz biz = new UserBiz();
    		try {
    			BUser user = biz.login(uname, pwd);
    			if(user != null){
    				request.getSession().setAttribute("user", user);
    				//使用cookie实现自动登录
    				Cookie cookie = new Cookie("user",uname+","+pwd);
    				cookie.setMaxAge(60*60*24);//设置生命周期
    				response.addCookie(cookie);
    				//统计在线用户数
    				OnlineUser.addUser(request.getSession().getId(), user);
    				System.out.println(user.getUname() + "登录成功！当前在线人数：" + OnlineUser.getUsers().size());
    				request.getRequestDispatcher("/MainSvl").forward(request, response);
    			}else{
    				request.setAttribute("msg", "用户名或密码错误");
    				request.getRequestDispatcher("/WEB-INF/main/login.jsp").forward(request, response);
    			}
    		} catch (Exception e) {
    			e.printStackTrace();
    			request.setAttribute("errMsg", "网络异常，请和管理员联系");
    			request.getRequestDispatcher("/error.jsp").forward(request, response);
    		}
    	}

**index.jsp**

<%@page import="javax.servlet.jsp.tagext.TryCatchFinally"%>
    <%@ page language="java" import="java.util.*,com.icss.biz.*,com.icss.entity.*,com.icss.util.*" pageEncoding="UTF-8"%>
    <%
    String path = request.getContextPath();
    String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
    // 自动登录校验
    Object  obj = request.getSession().getAttribute("user");
    if(obj == null){
    	Cookie[] cookies = request.getCookies();
    	if(cookies != null){
    		for(int i = 0; i < cookies.length; i++){
    			Cookie cookie = cookies[i];
    			if(cookie.getName().equals("user")){
    				String value = cookie.getValue();
    				String [] upwd = value.split(",");
    				UserBiz biz = new UserBiz();
    				try{
    					BUser buser = biz.login(upwd[0], upwd[1]);
    					if(buser != null){
    						request.getSession().setAttribute("user", buser);
    					}
    				}catch(Exception e){
    					Log.logger.error(e.getMessage());
    				}
    				break;
    			}
    		}
    	}
    }
    request.getRequestDispatcher("/MainSvl").forward(request,response);
    %>
    
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
    <html>
      <head>
        <base href="<%=basePath%>">
        
        <title>My JSP 'index.jsp' starting page</title>
    	<meta http-equiv="pragma" content="no-cache">
    	<meta http-equiv="cache-control" content="no-cache">
    	<meta http-equiv="expires" content="0">    
    	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    	<meta http-equiv="description" content="This is my page">
    	
      </head>
      
      <body>
        This is my JSP page. <br>
      </body>
    </html>

**为什么在jsp页面中进行校验？**  
      在用户访问通过项目名访问时，会在index.jsp页面转发到MainServlet，进行主页展示。当用户在LogoutServlet退出时，会重定向到MainServlet。如果在MainServlet中进行自动登录校验，则会发生**无法退出**的情况。

\*其他优秀博文\*：http://blog.163.com/xiexueyong1987@126/blog/static/126267342201031993557704/

[Cookie_Session]: http://blog.csdn.net/sinat_36553913/article/details/75905563
[SouthEast]: /images/20220607/db0b30bde8bf4cdd8ba818d779cc33f9.png