概念
Cookie是存储在客户端计算机上的文本文件，并保留了各种跟踪信息。Java Servlet支持HTTP Cookie。
识别返回用户包括三个步骤：
(1) 服务器脚本向浏览器发送一组Cookie。例如：姓名、年龄或识别号码等。
(2) 浏览器将这些信息存储在本地计算机上，以备将来使用。
(3) 当下一次浏览器向Web服务器发送任何请求时，浏览器会把这些Cookie信息发送到服务器，服务器将使用这些信息来识别用户。
注意事项
(1) 创建一个Cookie对象(注意要Encode / 无论是名字还是值，都不应该包含这字符: [ ] ( ) = , " / ? @ : ;)
Cookie name = new Cookie("name", URLEncoder.encode(request.getParameter("name"), "UTF-8"));
(2) 设置Cookie的有效时间(当设置0时意思为删除Cookie)
cookie.setMaxAge(60*60*24);
cookie.setMaxAge(0);
例子
(1) 登录成功后，[Welcome.Servlet]Response了两个Cookie: userId, password给浏览器
(2) 浏览器点[返回],发送Request给[Login.Servlet]并且把Cookie信息又发送到服务器
(3) 最终[Login.Servlet]Response了Cookie的一览信息
1 package com.servlettest.cookie; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.annotation.WebServlet; 8 import javax.servlet.http.Cookie; 9 import javax.servlet.http.HttpServlet; 10 import javax.servlet.http.HttpServletRequest; 11 import javax.servlet.http.HttpServletResponse; 12 13 /** 14 * Servlet implementation class Login 15 */ 16 @WebServlet("/login") 17 public class Login extends HttpServlet { 18 19 private static final long serialVersionUID = 1L; 20 21 /** 22 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 23 */ 24 @Override 25 protected void doGet(HttpServletRequest request, HttpServletResponse response) 26 throws ServletException, IOException { 27 28 response.setContentType("text/html"); 29 30 request.setCharacterEncoding("UTF-8"); 31 response.setCharacterEncoding("UTF-8"); 32 33 // 获取Session 34 Cookie[] cookies = request.getCookies(); 35 36 PrintWriter out = response.getWriter(); 37 out.println("<!DOCTYPE html>"); 38 out.println("<html>"); 39 out.println("<head>"); 40 out.println("<title>Login Page</title>"); 41 out.println("</head>"); 42 out.println("<body>"); 43 if (cookies != null && cookies.length > 0) { 44 out.println("<p>Cookies:</p>"); 45 out.println("<table border="1">"); 46 out.println( 47 "<tr><td>Name</td><td>Comment</td><td>Domain</td><td>MaxAge</td><td>Path</td><td>Value</td><td>Version</td></tr>"); 48 for (int i = 0; i < cookies.length; i++) { 49 out.println("<tr>"); 50 out.println("<td>" + cookies[i].getName() + "</td>"); 51 out.println("<td>" + cookies[i].getComment() + "</td>"); 52 out.println("<td>" + cookies[i].getDomain() + "</td>"); 53 out.println("<td>" + cookies[i].getMaxAge() + "</td>"); 54 out.println("<td>" + cookies[i].getPath() + "</td>"); 55 out.println("<td>" + cookies[i].getValue() + "</td>"); 56 out.println("<td>" + cookies[i].getVersion() + "</td>"); 57 out.println("</tr>"); 58 } 59 out.println("</table>"); 60 out.println("<br/>"); 61 } 62 out.println("<form action="welcome" method="POST">"); 63 out.println("帐号: <input type="text" name="userId"/><br/>"); 64 out.println("密码: <input type="password" name="password"/><br/>"); 65 out.println("<input type="submit" value="提交"/>"); 66 out.println("</body>"); 67 out.println("</html>"); 68 } 69 70 /** 71 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 72 */ 73 @Override 74 protected void doPost(HttpServletRequest request, HttpServletResponse response) 75 throws ServletException, IOException { 76 doGet(request, response); 77 } 78 }
package com.servlettest.cookie; import java.io.IOException; import java.io.PrintWriter; import java.net.URLEncoder; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class Welcome */ @WebServlet("/welcome") public class Welcome extends HttpServlet { private static final long serialVersionUID = 1L; private static final int VALID_TIME = 60; /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("UTF-8"); String userId = request.getParameter("userId"); String password = request.getParameter("password"); PrintWriter out = response.getWriter(); out.println("<!DOCTYPE html>"); out.println("<html>"); out.println("<head>"); out.println("<title>Login Page</title>"); out.println("</head>"); out.println("<body>"); if ("123".equals(password)) { out.println("欢迎您, " + userId); // 创建Ssession addCookie(userId, password, response); } else { out.println("您的帐号或密码错误!"); } out.println("<a href = "login">返回</a>"); out.println("</body>"); out.println("</html>"); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } private void addCookie(String userId, String password, HttpServletResponse response) throws IOException { Cookie userIdCookie = new Cookie("userId", URLEncoder.encode(userId, "UTF-8")); Cookie passwordCookie = new Cookie("password", URLEncoder.encode(password, "UTF-8")); userIdCookie.setMaxAge(VALID_TIME); passwordCookie.setMaxAge(VALID_TIME); response.addCookie(userIdCookie); response.addCookie(passwordCookie); } }
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1"> <welcome-file-list> <welcome-file>login</welcome-file> </welcome-file-list> </web-app>