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 }
Questionnaire.java
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 }
autoindex.java
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 }
autologin.java
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 }
User.java
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 }
Search.java
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 }
Questionnaire.java
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 }
Login.java
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 }
Logout.java
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 }
count.java
运行结果：
时间： 2024-10-14 21:54:01