一、会话管理的基本原理
web应用程序的请求与响应是基于HTTP，为无状态的通信协议，服务器不会记得这次请求和下次请求的关系，如购物车，用户可能在多个购物网页之间采购商品，web应用程序必须有个方式来得知用户在这些网页中采购了哪些商品，这种记得此次请求与之后请求间关系的方式，就称为会话管理(Session Management).
1、使用隐藏域
隐藏域就是主动告知服务器多次请求间必要信息的方式之一。以问卷作答的为例，上一页的问卷答案，可以用隐藏域的方式放在下一页的窗体中，这样发送下一页窗体，就可以一并发送这些隐藏域，每一页的问卷答案就可以保留下来。上一次的结果如何成为下一页的隐藏域呢？做法之一就是将上一页的结果发送至服务器，由服务器将上一页结果以隐藏域的方式再响应给浏览器。
例1：程序中有两页问卷，第一页的结果会在第二页成为隐藏域，当第二页发送时，就可以看到两页问卷的所有答案。
1 package Session.Management; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 import java.io.UnsupportedEncodingException; 6 7 import javax.servlet.ServletException; 8 import javax.servlet.annotation.WebServlet; 9 import javax.servlet.http.HttpServlet; 10 import javax.servlet.http.HttpServletRequest; 11 import javax.servlet.http.HttpServletResponse; 12 import javax.servlet.http.HttpSession; 13 14 /** 15 * Servlet implementation class Questionnaire 16 */ 17 @WebServlet("/questionnaire") 18 public class Questionnaire extends HttpServlet { 19 private static final long serialVersionUID = 1L; 20 21 /** 22 * @see HttpServlet#HttpServlet() 23 */ 24 public Questionnaire() { 25 super(); 26 // TODO Auto-generated constructor stub 27 } 28 29 /** 30 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 31 */ 32 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 33 // TODO Auto-generated method stub 34 processRequest(request,response); 35 } 36 37 private void processRequest(HttpServletRequest request, 38 HttpServletResponse response) throws IOException { 39 // TODO Auto-generated method stub 40 request.setCharacterEncoding("UTF-8"); 41 response.setContentType("text/html;charset=UTF-8"); 42 PrintWriter out=response.getWriter(); 43 out.println("<!DOCTYPE html>"); 44 out.println("<html>"); 45 out.println("<head>"); 46 out.println("<meta content='text/html; charset=UTF-8' http-equiv='content-type'>"); 47 out.println("<title>Questionnaire</title>"); 48 out.println("</head>"); 49 out.println("<body>"); 50 String page=request.getParameter("page");//page请求参数决定哪一个页面问卷 51 out.println("<form action='questionnaire' method='post'>"); 52 if(page==null){ 53 out.println("问题一：<input type='text' name='p1q1'><br>"); 54 out.println("问题二：<input type='text' name='p1q2'><br>");//第一页的问卷题目 55 out.println("<input type='submit' name='page' value='下一页'>"); 56 }else if("下一页".equals(page)){ 57 String p1q1=request.getParameter("p1q1"); 58 String p1q2=request.getParameter("p1q2"); 59 60 //使用隐藏域 61 // out.println("<input type='hidden' name='p1q1' value='"+p1q1+"'>"); 62 // out.println("<input type='hidden' name='p1q2' value='"+p1q2+"'>"); 63 64 //使用HttpSession存储第一页的答案 65 HttpSession session=request.getSession(); 66 session.setAttribute("p1q1", p1q1); 67 session.setAttribute("p1q2", p1q2); 68 69 out.println("问题三：<input type='text' name='p2q1'><br>");//第二页的问卷题目 70 //out.println("问题四：<input type='text' name='p2q2'><br>"); 71 out.println("<input type='submit' name='page' value='完成'>");//第一页问卷答案，使用隐藏域发送答案 72 }else if("完成".equals(page)){ 73 74 HttpSession session=request.getSession(); 75 session.getAttribute("p1q1"); 76 77 out.println(session.getAttribute("p1q1")+"<br>"); 78 out.println(session.getAttribute("p1q2")+"<br>"); 79 out.println(request.getParameter("p2q1")+"<br>");//问卷结果网页 80 } 81 out.println("</form>"); 82 out.println("</body>"); 83 out.println("</html>"); 84 out.close(); 85 } 86 87 /** 88 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 89 */ 90 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 91 // TODO Auto-generated method stub 92 processRequest(request,response); 93 } 94 95 }
使用隐藏域的方式，在关掉网页后，显然会丢失先前的请求的信息，所以仅适合用于一些简单的状态管理，如在线问卷。在查看网页源代码时，就可以看到隐藏域的值，这个方法不适合隐秘性较高的数据。
2、使用Cookie
Cookie是在浏览器存储信息的一种方式，服务器可以响应浏览器set-cookie标头，浏览器收到这个标头与数值后，会将它以文件的形式存储在计算机上，这个文件就是Cookie。可以给Cookie设定一个存活期限，保留一些有用的信息在客户端，如果在关闭浏览器之后，再次打开浏览器并连接服务器时，这些cookie仍在有效期限中，浏览器会使用cookie标头自动将Cookie发送给服务器，服务器就可以得知一些先前请求的信息。
如果创建Cookie，可以使用Cookie类，创建时指定Cookie中的名称与数值，并使用HttpServletResponse的addCookie()方法在响应中新增Cookie。例如：
Cookie cookie=new Cookie("user","caterpillar");
cookie.setMaxAge(7*24*60*60);//单位是秒，所以一星期有效
response.addCookie(cookie);
如果想要取得浏览器上存储的Cookie，则可以HttpServletRequest的getCookie()来取得，这可取得属于该网页所有域的所有Cookie，所以返回值时cookie[]数组。取得cookie对象后，可以使用Cookie的getName()与getValues()方法，分别取得Cookie的名称和数值。
Cookie[] cookies=request.getCookies();
if(cookies != null){
for(Cookie cookie : cookies){
String name = cookie.getName();
String value = cookie.getValue();
}
}
例2：用Cookie实现自动登录功能。当访问首页时，会检查用户先前时是否允许自动登录，如果是的话，就直接转送至用户界面。
1 package Session.Management; 2 3 import java.io.IOException; 4 5 import javax.servlet.ServletException; 6 import javax.servlet.annotation.WebServlet; 7 import javax.servlet.http.Cookie; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 12 /** 13 * Servlet implementation class Index 14 */ 15 @WebServlet("/index.do") 16 public class Index extends HttpServlet { 17 private static final long serialVersionUID = 1L; 18 19 /** 20 * @see HttpServlet#HttpServlet() 21 */ 22 public Index() { 23 super(); 24 // TODO Auto-generated constructor stub 25 } 26 27 /** 28 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 29 */ 30 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 31 // TODO Auto-generated method stub 32 processRequest(request,response); 33 } 34 35 private void processRequest(HttpServletRequest request, 36 HttpServletResponse response) throws IOException, ServletException { 37 // TODO Auto-generated method stub 38 Cookie[] cookies=request.getCookies();//取得Cookie 39 if(cookies!=null){ 40 for(Cookie cookie:cookies){ 41 String name=cookie.getName(); 42 String value=cookie.getValue(); 43 if("user".equals(name)&&"caterpillar".equals(value)){ 44 request.setAttribute(name, value); 45 request.getRequestDispatcher("/user.view").forward(request, response); 46 return; 47 } 48 } 49 } 50 response.sendRedirect("index.html");//如果没有相对应的Cookie名称与数值，表示尚未允许自动登录，重定向到登录窗体。 51 52 } 53 54 /** 55 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 56 */ 57 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 58 // TODO Auto-generated method stub 59 processRequest(request,response); 60 } 61 62 }
运行结果：
1 package Session.Management; 2 3 import java.io.IOException; 4 5 import javax.servlet.ServletException; 6 import javax.servlet.annotation.WebServlet; 7 import javax.servlet.http.Cookie; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 12 /** 13 * Servlet implementation class Login1 14 */ 15 @WebServlet("/login1.do") 16 public class Login1 extends HttpServlet { 17 private static final long serialVersionUID = 1L; 18 19 /** 20 * @see HttpServlet#HttpServlet() 21 */ 22 public Login1() { 23 super(); 24 // TODO Auto-generated constructor stub 25 } 26 27 /** 28 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 29 */ 30 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 31 // TODO Auto-generated method stub 32 } 33 34 /** 35 * *- 36 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 37 */ 38 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 39 // TODO Auto-generated method stub 40 String user=request.getParameter("user"); 41 String passwd=request.getParameter("password"); 42 if("nihao".equals(user)&&"123456789".equals(passwd)){ 43 // String login=request.getParameter("login"); 44 // if("auto".equals(login)){ 45 // Cookie cookie=new Cookie("user", "nihao"); 46 // cookie.setMaxAge(7*24*60*60); 47 // response.addCookie(cookie); 48 // } 49 //request.setAttribute("user", user); 50 51 request.getSession().setAttribute("login", user); 52 53 request.getRequestDispatcher("user.view").forward(request, response); 54 }else{ 55 response.sendRedirect("index.html"); 56 } 57 } 58 59 }
1 package Session.Management; 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.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 import javax.servlet.http.HttpSession; 12 13 /** 14 * Servlet implementation class User 15 */ 16 @WebServlet("/user.view") 17 public class User extends HttpServlet { 18 private static final long serialVersionUID = 1L; 19 20 /** 21 * @see HttpServlet#HttpServlet() 22 */ 23 public User() { 24 super(); 25 // TODO Auto-generated constructor stub 26 } 27 28 /** 29 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 30 */ 31 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 32 // TODO Auto-generated method stub 33 processRequest(request,response); 34 } 35 36 private void processRequest(HttpServletRequest request, 37 HttpServletResponse response) throws IOException { 38 // TODO Auto-generated method stub 39 response.setContentType("text/html;charset=UTF-8"); 40 HttpSession session=request.getSession(); 41 if(session.getAttribute("login")==null){ 42 response.sendRedirect("index.html"); 43 }else{ 44 PrintWriter out=response.getWriter(); 45 out.println("<!DOCTYPE html>"); 46 out.println("<html>"); 47 out.println("<head>"); 48 out.println("<meta content='text/html; charset=UTF-8' http-equiv='content-type'>"); 49 out.println("<title>欢迎"+session.getAttribute("login")+"</title>"); 50 out.println("</head>"); 51 out.println("<body>"); 52 out.println("<h1>用户 "+session.getAttribute("login")+"已登录</h1><br><br>"); 53 out.println("<a href='logout.view'>注销</a>"); 54 out.println("</body>"); 55 out.println("</html>"); 56 out.close(); 57 } 58 59 } 60 61 /** 62 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 63 */ 64 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 65 // TODO Auto-generated method stub 66 processRequest(request,response); 67 } 68 69 }
当登录名正确时候，下次再次登录atuoindex.java时就会自动登录，并转到user.java
3、使用URL重写
所谓URL重写，其实就是GET请求参数的应用，当服务器响应浏览器上一次请求时，将某些信息以超链接的方式响应给浏览器，超链接中包括请求参数信息。
例3：模拟搜索分页结果，比如当点击第五页的时候，就会显示第五页的内容。
1 package Session.Management; 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.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 12 /** 13 * Servlet implementation class Search 14 */ 15 @WebServlet("/search") 16 public class Search extends HttpServlet { 17 private static final long serialVersionUID = 1L; 18 19 /** 20 * @see HttpServlet#HttpServlet() 21 */ 22 public Search() { 23 super(); 24 // TODO Auto-generated constructor stub 25 } 26 27 /** 28 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 29 */ 30 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 31 // TODO Auto-generated method stub 32 response.setContentType("text/html;charset=UTF-8"); 33 34 PrintWriter out=response.getWriter(); 35 out.println("<!DOCTYPE html>"); 36 out.println("<html>"); 37 out.println("<head>"); 38 out.println("<meta content='text/html; charset=UTF-8' http-equiv='content-type'>"); 39 out.println("<title>搜索结果</title>"); 40 out.println("</head>"); 41 out.println("<body>"); 42 String start=request.getParameter("start"); 43 while(start==null){ 44 start="1"; 45 } 46 int count=Integer.parseInt(start); 47 int begin=10*count-9; 48 int end=10*count; 49 out.println("第 "+begin+" 到 "+end+" 搜索结果<br>"); 50 out.println("<ul>"); 51 for(int i=1;i<=10;i++){ 52 out.println("<li>搜寻结果"+i+"</li>"); 53 } 54 out.println("</ul>"); 55 for(int i=1;i<10;i++){ 56 if(i==count){ 57 out.println(i); 58 continue; 59 } 60 out.println("<a href='search?start="+i+"'>"+i+"</a>"); 61 } 62 out.println("</body>"); 63 out.println("</html>"); 64 out.close(); 65 } 66 67 /** 68 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 69 */ 70 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 71 // TODO Auto-generated method stub 72 73 } 74 75 }
运行结果：
二、HttpSession会话管理
可以将必须共享的数据，保存在HttpSession中成为属性，当关掉浏览器接收Cookie的功能，HttpSession也可以改用URL重写继续其会话管理。
1、使用HttpSession
使用HttpServletRequest的getSession()方法取得HttpSession对象。
HttpSession session = request.getSession();
HttpSession最常用的方法大概是setAttribute()与getAttribute()，这与HttpServletRequest的setAttribute()和getAttribute()类似，可以让你在对象中设置及取得属性，这是可以存放属性的第二个地方。(ServletAPI 中第三个可以存放属性的地方是在ServletContext中)。
例3：将例1的在线问答，从隐藏域改为HttpSession方式来实现会话管理。
1 package Session.Management; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 import java.io.UnsupportedEncodingException; 6 7 import javax.servlet.ServletException; 8 import javax.servlet.annotation.WebServlet; 9 import javax.servlet.http.HttpServlet; 10 import javax.servlet.http.HttpServletRequest; 11 import javax.servlet.http.HttpServletResponse; 12 import javax.servlet.http.HttpSession; 13 14 /** 15 * Servlet implementation class Questionnaire 16 */ 17 @WebServlet("/questionnaire") 18 public class Questionnaire extends HttpServlet { 19 private static final long serialVersionUID = 1L; 20 21 /** 22 * @see HttpServlet#HttpServlet() 23 */ 24 public Questionnaire() { 25 super(); 26 // TODO Auto-generated constructor stub 27 } 28 29 /** 30 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 31 */ 32 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 33 // TODO Auto-generated method stub 34 processRequest(request,response); 35 } 36 37 private void processRequest(HttpServletRequest request, 38 HttpServletResponse response) throws IOException { 39 // TODO Auto-generated method stub 40 request.setCharacterEncoding("UTF-8"); 41 response.setContentType("text/html;charset=UTF-8"); 42 PrintWriter out=response.getWriter(); 43 out.println("<!DOCTYPE html>"); 44 out.println("<html>"); 45 out.println("<head>"); 46 out.println("<meta content='text/html; charset=UTF-8' http-equiv='content-type'>"); 47 out.println("<title>Questionnaire</title>"); 48 out.println("</head>"); 49 out.println("<body>"); 50 String page=request.getParameter("page");//page请求参数决定哪一个页面问卷 51 out.println("<form action='questionnaire' method='post'>"); 52 if(page==null){ 53 out.println("问题一：<input type='text' name='p1q1'><br>"); 54 out.println("问题二：<input type='text' name='p1q2'><br>");//第一页的问卷题目 55 out.println("<input type='submit' name='page' value='下一页'>"); 56 }else if("下一页".equals(page)){ 57 String p1q1=request.getParameter("p1q1"); 58 String p1q2=request.getParameter("p1q2"); 59 60 //使用隐藏域 61 // out.println("<input type='hidden' name='p1q1' value='"+p1q1+"'>"); 62 // out.println("<input type='hidden' name='p1q2' value='"+p1q2+"'>"); 63 64 //使用HttpSession存储第一页的答案 65 HttpSession session=request.getSession(); 66 session.setAttribute("p1q1", p1q1); 67 session.setAttribute("p1q2", p1q2); 68 69 out.println("问题三：<input type='text' name='p2q1'><br>");//第二页的问卷题目 70 //out.println("问题四：<input type='text' name='p2q2'><br>"); 71 out.println("<input type='submit' name='page' value='完成'>");//第一页问卷答案，使用隐藏域发送答案 72 }else if("完成".equals(page)){ 73 74 HttpSession session=request.getSession(); 75 session.getAttribute("p1q1"); 76 77 out.println(session.getAttribute("p1q1")+"<br>"); 78 out.println(session.getAttribute("p1q2")+"<br>"); 79 out.println(request.getParameter("p2q1")+"<br>");//问卷结果网页 80 } 81 out.println("</form>"); 82 out.println("</body>"); 83 out.println("</html>"); 84 out.close(); 85 } 86 87 /** 88 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 89 */ 90 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 91 // TODO Auto-generated method stub 92 processRequest(request,response); 93 } 94 95 }
默认在浏览器关闭之前，取得HttpSession都是相同的实例。如果在次会话期间，直接让目前的HttpSession失效，可以执行HttpSession的invalidate()方法，一个使用的时机是实现注销机制。
例4：注销机制。
1 package Session.Management; 2 3 import java.io.IOException; 4 5 import javax.servlet.ServletException; 6 import javax.servlet.annotation.WebServlet; 7 import javax.servlet.http.Cookie; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 12 /** 13 * Servlet implementation class Login1 14 */ 15 @WebServlet("/login1.do") 16 public class Login1 extends HttpServlet { 17 private static final long serialVersionUID = 1L; 18 19 /** 20 * @see HttpServlet#HttpServlet() 21 */ 22 public Login1() { 23 super(); 24 // TODO Auto-generated constructor stub 25 } 26 27 /** 28 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 29 */ 30 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 31 // TODO Auto-generated method stub 32 } 33 34 /** 35 * *- 36 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 37 */ 38 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 39 // TODO Auto-generated method stub 40 String user=request.getParameter("user"); 41 String passwd=request.getParameter("password"); 42 if("nihao".equals(user)&&"123456789".equals(passwd)){ 43 // String login=request.getParameter("login"); 44 // if("auto".equals(login)){ 45 // Cookie cookie=new Cookie("user", "nihao"); 46 // cookie.setMaxAge(7*24*60*60); 47 // response.addCookie(cookie); 48 // } 49 //request.setAttribute("user", user); 50 51 request.getSession().setAttribute("login", user); 52 53 request.getRequestDispatcher("user.view").forward(request, response); 54 }else{ 55 response.sendRedirect("index.html"); 56 } 57 } 58 59 }
1 package Session.Management; 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.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 import javax.servlet.http.HttpSession; 12 13 /** 14 * Servlet implementation class Logout 15 */ 16 @WebServlet("/logout.view") 17 public class Logout extends HttpServlet { 18 private static final long serialVersionUID = 1L; 19 20 21 /** 22 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 23 */ 24 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 25 // TODO Auto-generated method stub 26 response.setContentType("text/html;charset=UTF-8"); 27 HttpSession session=request.getSession(); 28 String user=(String) session.getAttribute("login"); 29 session.invalidate();//使HttpSession失效 30 31 PrintWriter out=response.getWriter(); 32 out.println("<!DOCTYPE html>"); 33 out.println("<html>"); 34 out.println("<head>"); 35 out.println("<meta content='text/html; charset=UTF-8' http-equiv='content-type'>"); 36 out.println("<title>注销</title>"); 37 out.println("</head>"); 38 out.println("<body>"); 39 out.println("<h1>用户 "+user+"已注销</h1>"); 40 out.println("</body>"); 41 out.println("</html>"); 42 out.close(); 43 } 44 45 46 47 }
2、HttpSession会话管理原理
尝试运行HttpServletRequest的getSession()时，web容器会创建HttpSession()对象，关键在每个HttpSession对象都有个特殊的ID,成为Session ID，你可以执行HttpSession的getId()来取得Session ID。这个Session ID会默认使用Cookie存放在浏览器中。当浏览器请求应用程序时，会找Cookie存放的Session ID一并发送给应用程序，Web容器会根据Session ID来找出对应的HttpSession对象，这样就可以取得各浏览器个别的会话数据。
使用HttpSession来进行进行会话管理时，设定为属性的对象是存储在服务器端，而Session ID默认使用Cookie存放于浏览器端。web容器存储Session ID的Cookie默认为关闭浏览器就失效。(默认关闭浏览器会马上失效的是浏览器上的Cookie，而不是HttpSession，要让HttpSesson立即失效必须运行invalidate()方法，或者等到设定的失效期间过后才会被容器销毁回收。)
使用setMaxInactiveInterval()方法，设定浏览器多久没有请求的话，HttpSession自动失效。
3、HttpSession与URL重写
HttpSession默认使用Cookie存储Session ID，如果用户关闭浏览器接收Cookie的功能，就无法使用Cookie在浏览器存储SessionID，如果在用户禁用Cookie的情况下，扔打算用HttpSession来进行会话管理，就可以搭配URL重写，向浏览器响应一段超链接，超链接URL后附加Session ID，当用户点击超链接时，将Session ID以GET请求发送给Web应用程序。
如：<a href='"+response.encodeURL("counter")+"'>递增</a>
例5：实现页面自增1
1 package Session.Management; 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.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 import javax.servlet.http.HttpSession; 12 13 /** 14 * Servlet implementation class Counter 15 */ 16 @WebServlet("/counter") 17 public class Counter extends HttpServlet { 18 private static final long serialVersionUID = 1L; 19 20 /** 21 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 22 */ 23 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 24 // TODO Auto-generated method stub 25 response.setContentType("text/html;charset=UTF-8"); 26 27 PrintWriter out=response.getWriter(); 28 int count=0; 29 HttpSession session=request.getSession(); 30 if(session.getAttribute("count")!=null){ 31 Integer c=(Integer) session.getAttribute("count"); 32 count=c+1; 33 } 34 session.setAttribute("count", count); 35 out.println("<!DOCTYPE html>"); 36 out.println("<html>"); 37 out.println("<head>"); 38 out.println("<meta content='text/html; charset=UTF-8' http-equiv='content-type'>"); 39 out.println("<title>注销</title>"); 40 out.println("</head>"); 41 out.println("<body>"); 42 out.println("<h1>Servlet Count "+count+"</h1>"); 43 out.println("<a href='"+response.encodeURL("counter")+"'>递增</a>");//使用encodeURL 44 out.println("</body>"); 45 out.println("</html>"); 46 out.close(); 47 } 48 }
运行结果：
当神已无能为力，那便是魔渡众生
