Session

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Session:

Session实现原理:

浏览器未禁用Cookie:

Jsp代码：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>My JSP 'index.jsp' starting page</title>  </head>    <body>    <a href="/day07/servlet/SessionDemo1">购买</a>    <a href="/day07/servlet/SessionDemo2">结账</a>  </body></html>

Servlet代码：

//购买public class SessionDemo1 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//第一次getSession时创建Session，默认30分钟没人用Session就自动摧毁了HttpSession session = request.getSession();//Session技术是基于Cookie技术实现的，每次创建完Session，都会将JSESSIONID写给浏览器//但是默认存放JSESSIONID的Cookie有效时间为0，即关闭浏览器Cookie就消失，所以默认情况下，一个浏览器独占一个Session//所以电子商务网站必须有以下过程，手动设置存放JSESSIONID的Cookie的有效时间和Session的一致//即重写存放JSESSIONID的Cookie,这样就实现了多浏览共享一个Session，即关闭浏览器再打开也能得到上次的SessionString sessionid = session.getId();Cookie cookie = new Cookie("JSESSIONID",sessionid);cookie.setPath("/day07");cookie.setMaxAge(30*60);response.addCookie(cookie);session.setAttribute("name", "洗衣机");//不创建只获取,用于显示购物车,有人闲的不买直接结账查看购物车，这时不必创建session//request.getSession(false);//invalidate摧毁Session，或者在web.xml里<session-config>配置摧毁时间//session.invalidate();}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//结账public class SessionDemo2 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setCharacterEncoding("UTF-8");response.setHeader("content-Type", "text/html;charset=utf-8");PrintWriter out = response.getWriter();HttpSession session = request.getSession(false);String product = (String)session.getAttribute("name");out.write("您购买的商品是："+product); }public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

浏览器禁用Cookie:

Servlet代码：

//首页public class WelcomeServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setCharacterEncoding("UTF-8");response.setHeader("Content-Type", "text/html;charset=UTF-8");PrintWriter out = response.getWriter();//一访问首页自动创建Session，getSession首先检查cookie是否有JSESSIONID，再检查url后是否有JSESSIONID,如果都没有则新创建个Sessionrequest.getSession();//如果禁用了cookie，那么电子商务使用Session则需要重写url(但是这种方法却无法解决关闭浏览器再打开后，获取上一次Session)//让用户点击超链接自动带上JSESSIONID//以下两句实现了Url地址后自动加上JSESSIONID，Sun公司提供的方法//如果服务器发现用户没有禁用cookie，则不会重写url(第一次访问服务器既重写url又返回cookie，第二次访问，服务器发现有cookie，则url不会带参数)String url1 = response.encodeRedirectURL("/day07/servlet/SessionDemo1");String url2 = response.encodeRedirectURL("/day07/servlet/SessionDemo2");out.print("<a href='"+url1+"'>购买</a>    ");out.print("<a href='"+url2+"'>结账</a>");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

Session案例——实现简单的购物:

Servlet代码：

//商品类（书籍）class Book{private String id;private String name;private String author;private String description;public Book() {super();// TODO Auto-generated constructor stub}public Book(String id, String name, String author, String description) {super();this.id = id;this.name = name;this.author = author;this.description = description;}public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}}

//数据库(如果有检索数据需求，则用双列(Map)，如果不检索，则用单列(List))class Db{private static Map<String,Book> map = new LinkedHashMap();  //如果用HashMap，则获取商品顺序和存入顺序不一致，hashMap是根据hash值排列的//静态块，一使用Db类就自动执行static{map.put("1", new Book("1","javaweb开发","老张","一本好书"));map.put("2", new Book("2","jdbc开发","老张","一本好书"));map.put("3", new Book("3","spring开发","老黎","一本好书"));map.put("4", new Book("4","struts开发","老毕","一本好书"));map.put("5", new Book("5","android开发","老黎","一本好书"));}public static Map getAll(){return map;}}

//代表网站首页，列出所有书public class ListBookServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//以后学习过滤器filter，设置一次，则所有资源都解决中文乱码，不必每次都设置response.setCharacterEncoding("UTF-8");response.setHeader("Content-Type", "text/html;charset=UTF-8");PrintWriter out = response.getWriter();request.getSession();//一访问首页就建立session，以防cookie禁用,则用重写urlout.print("本网站有如下商品：<br/>");Map<String,Book> map = Db.getAll();for(Map.Entry<String, Book> entry : map.entrySet()){Book book = (Book)entry.getValue();String url = response.encodeRedirectURL(request.getContextPath()+"/servlet/BuyServlet?id="+book.getId());out.print(book.getName()+" <a href='"+url+"' target='_blank'>购买</a><br/>");}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//完成购买public class BuyServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String id = request.getParameter("id");Book book = (Book)Db.getAll().get(id);HttpSession session = request.getSession(false);//手工以cookie形式发sessionid，来解决关闭浏览器后，上次买的东西还在String sessionid = session.getId();Cookie cookie = new Cookie("JSESSIONID",sessionid);cookie.setMaxAge(30*60);cookie.setPath(request.getContextPath());response.addCookie(cookie);//从Session中得到用户用于保存所有书的集合(得到用户的购物车)List list = (List)session.getAttribute("list");if(list==null){list = new ArrayList();session.setAttribute("list", list);}list.add(book);//到结账界面要用重定向response.setStatus(302);//最好不写死跳转路径，用request.getContextPath()得到当前web应用目录String url = response.encodeRedirectURL(request.getContextPath()+"/servlet/ListCartServlet");response.setHeader("Location", url);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//显示用户购买的商品public class ListCartServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setCharacterEncoding("UTF-8");response.setHeader("content-type", "text/html;charset=UTF-8");PrintWriter out = response.getWriter();HttpSession session = request.getSession(false);if(session==null){out.print("您没有购买任何商品!!");return;}out.print("您购买了如下商品：<br/>");List<Book> list = (List)session.getAttribute("list");for(Book book : list){out.print(book.getName()+"<br/>");}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

Session案例——完成用户的登录:
html代码：

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>login.html</title>  </head>    <body>    <form action="/day07/servlet/LoginServlet" method="post">    用户名：<input type="text" name="username"/><br/>    密码：<input type="password" name="password"/><br/>     <input type="submit" value="登录"/>        </form>  </body></html>

Servlet代码：

//用户类public class User {private String username;private String password;public User() {super();// TODO Auto-generated constructor stub}public User(String username, String password) {super();this.username = username;this.password = password;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}}

//数据库class DB{public static List list = new ArrayList();static{list.add(new User("aaa","123"));list.add(new User("bbb","123"));list.add(new User("ccc","123"));}public static List getAll(){return list;}}

//完成用户登录public class LoginServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setCharacterEncoding("UTF-8");response.setHeader("Content-Type", "text/html;charset=UTF-8");PrintWriter out = response.getWriter();String username = request.getParameter("username");String password = request.getParameter("password");List<User> list = DB.getAll();for(User user : list){if(user.getUsername().equals(username)&&user.getPassword().equals(password)){request.getSession().setAttribute("user", user);//登录成功，向Session存入一个登录标记response.setStatus(302);response.setHeader("Location", "/day07/index.jsp");return;}}out.write("用户名或密码不对！！");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

//完成用户注销public class LogoutServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {HttpSession session = request.getSession(false);if(session==null){response.setStatus(302);response.setHeader("Location", "/day07/index.jsp");return;}session.removeAttribute("user");response.setStatus(302);response.setHeader("Location", "/day07/index.jsp");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

Jsp代码：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>My JSP 'index.jsp' starting page</title>  </head>    <body>  欢迎您：${user.username} <a href="/day07/login.html">登录</a> <a href="/day07/servlet/LogoutServlet">退出登录</a>  <br/><br/><br/>    <a href="/day07/servlet/SessionDemo1">购买</a>    <a href="/day07/servlet/SessionDemo2">结账</a>  </body></html>

Session案例——防止表单重复提交:
客户端javascript防止表单重复提交：

html代码：

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>form.html</title>    <!-- 用js阻止表单重复提交(属于客户端阻止重复提交，不安全，用户可以自己重写提交页面或者刷新/后退页面继续提交)     但是还是要用客户端阻止一下，再用服务器阻止-->    <script type="text/javascript">    /*    var iscommitted = false;    function dosubmit(){    if(!iscommitted){    iscommitted=true;    return true;    }    else{    return false;    }    }    */    function dosubmit(){    var input = document.getElementById("submit");    input.disabled = 'disabled';    return true;    }    </script>  </head>    <body>    <form action="/day07/servlet/DoFormServlet" method="post" onsubmit="return dosubmit()">    用户名：<input type="text" name="username"/>    <input id="submit" type="submit" value="提交" />    </form>  </body></html>

服务器端session防止表单重复提交：

Servlet代码：

//令牌发生器，为了保证发生的令牌唯一性（低重复概率），要设计成单类class TokenProcessor{/** 单类设计方法： * 1.把构造方法私有 * 2.自己创建一个实例 * 3.对外暴露一个方法，允许获取上面创建的对象 */private TokenProcessor(){}private static final TokenProcessor instance = new TokenProcessor();public static TokenProcessor getInstance(){return instance;}//产生令牌(随机数)的方法public String generateToken(){//为了随机数尽可能唯一，令牌里用 当前毫秒值+随机数String token = System.currentTimeMillis() + new Random().nextInt() + "";try {//为了保证随机数长度固定，需要得到数据指纹(即数据摘要，只有128位（bit）,即16字节(byte))MessageDigest md = MessageDigest.getInstance("md5");//用md5算法算出数据摘要byte[] md5 = md.digest(token.getBytes());//得到数据摘要，数组长度始终未16//base64编码BASE64Encoder encoder = new BASE64Encoder();return encoder.encode(md5);} catch (NoSuchAlgorithmException e) {throw new RuntimeException(e);}}}

//产生表单public class FormServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//产生一个随机数(表单号)TokenProcessor tp = TokenProcessor.getInstance();String token = tp.generateToken();//服务器保存一份表单号(token)request.getSession().setAttribute("token", token);//转发到表单页面request.getRequestDispatcher("/form.jsp").forward(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

jsp代码：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>My JSP 'form.jsp' starting page</title>  </head>    <body>    <form action="/day07/servlet/DoFormServlet" method="post">    <input type="hidden" name="token" value="${token }"/>    用户名：<input type="text" name="username"/><br/>    <input type="submit" value="提交"/>    </form>  </body></html>

Servlet代码：

//处理表单public class DoFormServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {boolean b = isTokenValid(request);if(!b){System.out.println("请不要重复提交!");return;}request.getSession().removeAttribute("token");System.out.println("处理：向数据库注册用户~~~~");}//判断表单号是否有效private boolean isTokenValid(HttpServletRequest request) {//得到客户端提交表单时带的token（表单号）String client_token = request.getParameter("token");if(client_token==null){ //客户端未通过程序输出的表单提交，则不带tokenreturn false;}//得到服务器端session中存放的token(表单号)String server_token = (String)request.getSession().getAttribute("token");if(server_token==null){ //服务器端没有token，表示已经提交过了return false;}if(!client_token.equals(server_token)){ //客户端带来的token和服务器端token不一致return false;}return true;}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

Session案例——校验图片认证码:

Servlet代码：

//输出一张随机图片   public class ImageServlet extends HttpServlet {        public static final int WIDTH = 120;      public static final int HEIGHT = 35;            public void doGet(HttpServletRequest request, HttpServletResponse response)              throws ServletException, IOException {                    BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);                    Graphics g = image.getGraphics();                    //1.设置背景色           setBackground(g);                    //2.设置边框           setBorder(g);                    //3.画干扰线           drawRandomLine(g);                    //4.写随机数           String random = drawRandomNum((Graphics2D)g);          request.getSession().setAttribute("checkcode", random);                  //5.图形写给浏览器           response.setHeader("Content-Type", "image/jpeg");          //发头控制浏览器不要缓存           response.setDateHeader("expries", -1);          response.setHeader("Cache-Control", "no-cache");          response.setHeader("Pragma", "no-cache");                    ImageIO.write(image,"jpg",response.getOutputStream());                }            private void setBackground(Graphics g){          g.setColor(Color.WHITE);          g.fillRect(0, 0, WIDTH, HEIGHT);      }            private void setBorder(Graphics g){          g.setColor(Color.BLUE);          g.drawRect(1, 1, WIDTH-2, HEIGHT-2);      }            private void drawRandomLine(Graphics g){          g.setColor(Color.GREEN);          for(int i = 0 ;i < 5; i++){              int x1 = new Random().nextInt(WIDTH);              int y1 = new Random().nextInt(HEIGHT);                            int x2 = new Random().nextInt(WIDTH);              int y2 = new Random().nextInt(HEIGHT);                            g.drawLine(x1, y1, x2, y2);          }      }            private String drawRandomNum(Graphics2D g){                    g.setColor(Color.RED);          g.setFont(new Font("宋体",Font.BOLD,20));                    StringBuffer sb = new StringBuffer();        //[\u4e00-\u9fa5] 表示：所有的汉字在unicode编码4e00~9fa5之间           //常用汉字的unicode编码           String base = "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728\u4eba\u4eec\u6709\u6765\u4ed6\u8fd9\u4e0a\u7740\u4e2a\u5730\u5230\u5927\u91cc\u8bf4\u5c31\u53bb\u5b50\u5f97\u4e5f\u548c\u90a3\u8981\u4e0b\u770b\u5929\u65f6\u8fc7\u51fa\u5c0f\u4e48\u8d77\u4f60\u90fd\u628a\u597d\u8fd8\u591a\u6ca1\u4e3a\u53c8\u53ef\u5bb6\u5b66\u53ea\u4ee5\u4e3b\u4f1a\u6837\u5e74\u60f3\u751f\u540c\u8001\u4e2d\u5341\u4ece\u81ea\u9762\u524d\u5934\u9053\u5b83\u540e\u7136\u8d70\u5f88\u50cf\u89c1\u4e24\u7528\u5979\u56fd\u52a8\u8fdb\u6210\u56de\u4ec0\u8fb9\u4f5c\u5bf9\u5f00\u800c\u5df1\u4e9b\u73b0\u5c71\u6c11\u5019\u7ecf\u53d1\u5de5\u5411\u4e8b\u547d\u7ed9\u957f\u6c34\u51e0\u4e49\u4e09\u58f0\u4e8e\u9ad8\u624b\u77e5\u7406\u773c\u5fd7\u70b9\u5fc3\u6218\u4e8c\u95ee\u4f46\u8eab\u65b9\u5b9e\u5403\u505a\u53eb\u5f53\u4f4f\u542c\u9769\u6253\u5462\u771f\u5168\u624d\u56db\u5df2\u6240\u654c\u4e4b\u6700\u5149\u4ea7\u60c5\u8def\u5206\u603b\u6761\u767d\u8bdd\u4e1c\u5e2d\u6b21\u4eb2\u5982\u88ab\u82b1\u53e3\u653e\u513f\u5e38\u6c14\u4e94\u7b2c\u4f7f\u5199\u519b\u5427\u6587\u8fd0\u518d\u679c\u600e\u5b9a\u8bb8\u5feb\u660e\u884c\u56e0\u522b\u98de\u5916\u6811\u7269\u6d3b\u90e8\u95e8\u65e0\u5f80\u8239\u671b\u65b0\u5e26\u961f\u5148\u529b\u5b8c\u5374\u7ad9\u4ee3\u5458\u673a\u66f4\u4e5d\u60a8\u6bcf\u98ce\u7ea7\u8ddf\u7b11\u554a\u5b69\u4e07\u5c11\u76f4\u610f\u591c\u6bd4\u9636\u8fde\u8f66\u91cd\u4fbf\u6597\u9a6c\u54ea\u5316\u592a\u6307\u53d8\u793e\u4f3c\u58eb\u8005\u5e72\u77f3\u6ee1\u65e5\u51b3\u767e\u539f\u62ff\u7fa4\u7a76\u5404\u516d\u672c\u601d\u89e3\u7acb\u6cb3\u6751\u516b\u96be\u65e9\u8bba\u5417\u6839\u5171\u8ba9\u76f8\u7814\u4eca\u5176\u4e66\u5750\u63a5\u5e94\u5173\u4fe1\u89c9\u6b65\u53cd\u5904\u8bb0\u5c06\u5343\u627e\u4e89\u9886\u6216\u5e08\u7ed3\u5757\u8dd1\u8c01\u8349\u8d8a\u5b57\u52a0\u811a\u7d27\u7231\u7b49\u4e60\u9635\u6015\u6708\u9752\u534a\u706b\u6cd5\u9898\u5efa\u8d76\u4f4d\u5531\u6d77\u4e03\u5973\u4efb\u4ef6\u611f\u51c6\u5f20\u56e2\u5c4b\u79bb\u8272\u8138\u7247\u79d1\u5012\u775b\u5229\u4e16\u521a\u4e14\u7531\u9001\u5207\u661f\u5bfc\u665a\u8868\u591f\u6574\u8ba4\u54cd\u96ea\u6d41\u672a\u573a\u8be5\u5e76\u5e95\u6df1\u523b\u5e73\u4f1f\u5fd9\u63d0\u786e\u8fd1\u4eae\u8f7b\u8bb2\u519c\u53e4\u9ed1\u544a\u754c\u62c9\u540d\u5440\u571f\u6e05\u9633\u7167\u529e\u53f2\u6539\u5386\u8f6c\u753b\u9020\u5634\u6b64\u6cbb\u5317\u5fc5\u670d\u96e8\u7a7f\u5185\u8bc6\u9a8c\u4f20\u4e1a\u83dc\u722c\u7761\u5174\u5f62\u91cf\u54b1\u89c2\u82e6\u4f53\u4f17\u901a\u51b2\u5408\u7834\u53cb\u5ea6\u672f\u996d\u516c\u65c1\u623f\u6781\u5357\u67aa\u8bfb\u6c99\u5c81\u7ebf\u91ce\u575a\u7a7a\u6536\u7b97\u81f3\u653f\u57ce\u52b3\u843d\u94b1\u7279\u56f4\u5f1f\u80dc\u6559\u70ed\u5c55\u5305\u6b4c\u7c7b\u6e10\u5f3a\u6570\u4e61\u547c\u6027\u97f3\u7b54\u54e5\u9645\u65e7\u795e\u5ea7\u7ae0\u5e2e\u5566\u53d7\u7cfb\u4ee4\u8df3\u975e\u4f55\u725b\u53d6\u5165\u5cb8\u6562\u6389\u5ffd\u79cd\u88c5\u9876\u6025\u6797\u505c\u606f\u53e5\u533a\u8863\u822c\u62a5\u53f6\u538b\u6162\u53d4\u80cc\u7ec6";          int x = 5;  //第一个字的x坐标           for(int i = 0;i<4;i++){              int degree = new Random().nextInt()%30;//-30~30               String ch = base.charAt(new Random().nextInt(base.length()))+"";            sb.append(ch);              g.rotate(degree*Math.PI/180, x, 20);//设置旋转角度               g.drawString(ch, x, 20);              g.rotate(-degree*Math.PI/180, x, 20);              x = x + 30;          }          return sb.toString();    }            public void doPost(HttpServletRequest request, HttpServletResponse response)              throws ServletException, IOException {          doGet(request, response);      }    }

html代码：

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">  <html>    <head>      <title>register.html</title>      <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"/>         <script type="text/javascript">          function changeImage(img){              img.src = img.src + "?" + new Date().getTime();          }      </script>          </head>        <body>      <form action="/day07/servlet/RegisterServlet" method="post">          用户名：<input type="text" name="username"/><br/>          密码：<input type="password" name="password"/><br/>          认证码：<input type="text" name="checkcode"/>          <img src="/day07/servlet/ImageServlet" onclick="changeImage(this)" title="换一张" style="cursor:hand"/><br/>          <input type="submit" value="注册"/>      </form>    </body>  </html>

Servlet代码：

//处理注册请求public class RegisterServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//认证码是汉字，所以要设置一下request编码request.setCharacterEncoding("UTF-8");//处理注册请求之前，检验认证码是否有效String client_checkcode = request.getParameter("checkcode");String server_checkcode = (String)request.getSession().getAttribute("checkcode");if(client_checkcode!=null&&server_checkcode!=null&&client_checkcode.equals(server_checkcode)){System.out.println("client_checkcode = " + client_checkcode);System.out.println("server_checkcode = " + server_checkcode);System.out.println("处理注册请求!");}else{System.out.println("client_checkcode = " + client_checkcode);System.out.println("server_checkcode = " + server_checkcode);System.out.println("认证码错误!");}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}