会话技术

会话，现实生活中会话的含义：交谈、谈话。

在web访问过程中，会话代表什么意思呢？

浏览器打开一个网站，然后访问当前网站的诸多页面，最后关闭，整个的过程叫做一个会话。

HTTP协议，是一个无状态协议。在服务器看来，任何浏览器发送过来的请求数据都是完全相同的，一模一样，服务器是无法却别该请求来自于哪个浏览器。

比如：http://192.168.2.100/app/index.html

A和B用户同时访问了当前页面，发送的HTTP请求报文是完全相同的，对于服务器来说，它是无法区别该请求来自于a还是b

实际场景下，又有这样的需求，我们需要服务器可以给我们浏览器去保存一些数据，比如浏览记录、购物车

就会涉及到我们今天介绍的技术，会话技术。

会话技术i其实是为了解决HTTP协议无状态性而产生的一个解决方案。

会话技术可以分为两种，一个是客户端技术，一个是服务器技术。

客户端技术Cookie

Cookie是由服务器创建的，然后接下来，Cookie会被发送给客户端（响应报文，响应头 Set-Cookie:name=value），客户端会将cookie信息保存下来，下次再次访问服务器时，它会把整个cookie重新带回去给服务器（请求报文，请求头 Cookie:name=value），服务器接收到cookie（又由于cookie的值是唯一的），所以就可以利用cookie来进行会话管理。

服务器技术Session

Cookie

  1. package com.cskaoyan.cookie;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.Cookie;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.io.IOException;
  10. import java.util.Date;
  12. @WebServlet("/cookie1")
  13. public class CookieServlet extends HttpServlet {
  14.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  16.     }
  18.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  19.         //接收cookie的代码应该写在上面
  20.         Cookie[] cookies = request.getCookies();
  21.         if(cookies != null){
  22.             for (Cookie cookie : cookies) {
  23.                 if("lastVisit".equals(cookie.getName())){
  24.                     String value = cookie.getValue();
  25.                     Date date = new Date(Long.parseLong(value));
  26.                     response.getWriter().println(date);
  27.                 }
  28.             }
  29.         }
  30.         //在内部调用了getHeaders(Cookie)
  31.         //显示用户的上次访问时间
  32.         //生成cookie cookie的value值里面不能有空格
  33.         Cookie cookie = new Cookie("lastVisit", System.currentTimeMillis() + "");
  34.         // 以Set-Cookie响应头发送给客户端
  35.         //response.setHeader("Set-Cookie", "latLogin=xxx");
  36.         //EE规范同样给我们封装了一个简便的设置cookie的方法
  37.         response.addCookie(cookie);
  38.         //addCookie{
  39.         //    setHeader(Set-cookie, cookie.getName = cookie.getValue)
  40.         // }
  41.     }
  42. }

设置存活时间

cookie默认情况下只存在于浏览器的内存中，关闭浏览器，则cookie失效，如果希望cookie能够进行持久化保存，那么可以设置一个存活时间

  1. Cookie cookie = new Cookie("username", username);
  2. //单位是秒
  3. cookie.setMaxAge(180);

设置一个以秒为单位的时间（正数），表示它会在硬盘上存活多久，如果设置的是负数，和不设置是一样的

0表示的是删除cookie

  1. package com.cskaoyan.cookie;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.Cookie;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.io.IOException;
  11. @WebServlet("/login")
  12. public class LoginServlet extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  14.         request.setCharacterEncoding("utf-8");
  15.         response.setContentType("text/html;charset=utf-8");
  16.         String username = request.getParameter("username");
  17.         String password = request.getParameter("password");
  18.         //假设登录成功，那么需要将用户名放入到cookie中
  19.         Cookie cookie = new Cookie("username", username);
  20.         //单位是秒
  21.         cookie.setMaxAge(180);
  22.         response.addCookie(cookie);
  23.         response.getWriter().println("登录成功，即将跳转至个人主页....");
  24.         response.setHeader("refresh", "2;url=" + request.getContextPath() + "/info");
  25.     }
  27.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  29.     }
  30. }
  1. package com.cskaoyan.cookie;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.Cookie;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.io.IOException;
  11. @WebServlet("/info")
  12. public class InfoServlet extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         response.setContentType("text/html;charset=utf-8");
  19.         Cookie[] cookies = request.getCookies();
  20.         if(cookies != null){
  21.             for (Cookie cookie : cookies) {
  22.                 if("username".equals(cookie.getName())){
  23.                     response.getWriter().println("欢迎您，" + cookie.getValue());
  24.                     //0表示删除cookie
  25.                     cookie.setMaxAge(0);
  26.                     response.addCookie(cookie);
  27.                 }
  28.             }
  29.         }
  30.     }
  31. }

设置路径

默认情况下，当访问当前服务器下面所有的资源时，默认都会携带cookie，如果希望仅某些页面去携带cookie，那么可以设置一个path

  1. package com.cskaoyan.cookie.path;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.Cookie;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.io.IOException;
  11. @WebServlet("/path1")
  12. public class PathServlet1 extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         Cookie cookie = new Cookie("key", "path");
  19.         //直接写/应用名开头的路径
  20.         cookie.setPath(request.getContextPath() + "/path2");
  21.         response.addCookie(cookie);
  22.     }
  23. }
  1. package com.cskaoyan.cookie.path;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.Cookie;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.io.IOException;
  11. @WebServlet("/path2")
  12. public class PathServlet2 extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         //如果cookie设置了path，这个时候希望将cookie删除，那么可以怎么做呢
  19.         //需要特别注意一点，在删除cookie的时候，有一个注意事项，如果当前cookie设置了path
  20.         //那么删除cookie的时候，需要再将path再写一遍
  21.         //注意：删除cookie时浏览器删除
  22.         Cookie[] cookies = request.getCookies();
  23.         if(cookies != null){
  24.             for (Cookie cookie : cookies) {
  25.                 if("key".equals(cookie.getName())){
  26.                     response.getWriter().println(cookie.getValue());
  27.                     cookie.setMaxAge(0);
  28.                     cookie.setPath(request.getContextPath() + "/path2");
  29.                     response.addCookie(cookie);
  30.                 }
  31.             }
  32.         }
  33.     }
  34. }

设置域名

注意：cookie有一个大的原则，不可以设置和当前域名无关的cookie，比如当前域名localhost，然后你设置了一个域名叫做cskaoyan.com的cookie，那么其实时设置不成功的。

aaa.com ——— 你申请的

sub.aaa.com ———- 这个域名是属于你的

third.sub.aaa.com————这个域名也是属于你的

父子域名

如果你设置了一个aaa.com域名的cookie，那么默认情况下，下面所有的子域名都可以共享该cookie

  1. package com.cskaoyan.cookie.domain;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.Cookie;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.io.IOException;
  11. @WebServlet("/domain2")
  12. public class DomainServlet2 extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         Cookie cookie = new Cookie("user", "aaa.com");
  19.         cookie.setDomain("aaa.com");
  20.         response.addCookie(cookie);
  21.     }
  22. }

cookie的优缺点

优点：小、轻便、放在浏览器，服务器没有压力

缺点：存储数据比较少，value值只能是字符串类型，有限制；安全问题；

cookie其实可以用来存放一些非敏感性数据，

Session

服务器技术。session对象是在服务器产生的，但是呢，保存也是在服务器上面。

session你可以认为是服务器给每个浏览器所开辟的一块内存空间，将这块内存空间和浏览器做一个绑定，如果今后当前浏览器再次访问服务器，如果需要进行数据的存取，那么就放置在当前内存空间中。

浏览器在访问session的时候，session会给浏览器创建一个独一无二的session对象，session对象有一个id，会把session的id加上响应报文中发送给客户端，客户端接收到之后将其保存，下次再次访问服务器时，将该id再携带回来，服务器就可以取出session的id值，那么就可以拿到原先的session对象。

只需要记住一点，每个浏览器拿到的都是不同的session对象。

创建session

会话技术 - 图1

本质：请求头中是否有Cookie:JSESSIONID=XXXX

第一次访问，请求头中肯定没有Cookie:JSESSIONID=xxxx,所以执行到request.getSession的时候，那么就会创建一个session对象，同时以set-Cookie：JSESSIONID=xxxx将session的id返回给浏览器，浏览器会将id保存下来

第二次访问，请求头中会携带Cookie:JSESSIONID=xxxx,所以执行到request.getSession的时候，（根据session的id去找到对应的session对象），就i把当前的session对象返回。

关闭服务器，session对象会销毁吗

肯定会。

关闭浏览器，session对象会销毁吗

没有销毁。此时session对象类似不可达。不可达的原因在于cookie请求头默认情况下只存在浏览器的内存中，关闭浏览器则失效，

JSESSIONID就会丢失。

session的使用

存取数据。

session域。

关闭服务器，重启服务器，还可以访问到原先session中的数据吗

注意：不要使用idea的tomcat关闭来验证，否则你将得不到正确的结论。

还可以进一步验证，比如使用本地的tomcat来部署我们的应用。

需要使用tomcat自带的管理系统来将应用给卸载。

在本地安装的tomcat conf/tomcat-users.xml文件中增加如下设置

  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import javax.servlet.http.HttpSession;
  9. import java.io.IOException;
  11. @WebServlet("/session1")
  12. public class SessionServlet extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         //如何去创建一个session呢？
  19.         HttpSession session = request.getSession();
  20.         session.setAttribute("username", "zhangsan");
  21.         System.out.println(session.getId());
  22.         System.out.println(session);
  23.     }
  24. }
  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import javax.servlet.http.HttpSession;
  9. import java.io.IOException;
  11. @WebServlet("/session2")
  12. public class SessionServlet2 extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         //如何去创建一个session呢？
  19.         HttpSession session = request.getSession();
  20.         String username = (String) session.getAttribute("username");
  21.         System.out.println(session.getId());
  22.         System.out.println(session);
  23.         System.out.println(username);
  24.     }
  25. }

会话技术 - 图2

最终session里面的数据还是存在的，还可以访问到。session的地址发生了变化，但是session的id没有变。

秽土转生。

session在临死之前，它会序列化到本地硬盘上面（把里面的id、attributes属性全部序列化到本地硬盘上面），形成一个文件，当应用重新被启动的时候，读取文件，将里面的数据重新读取到内存中，会创建新的session，将这些id、属性值全部赋值给新的session对象。

关闭浏览器，如果我希望还可以访问到原先session中的数据，应该怎么办

  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.*;
  6. import java.io.IOException;
  8. @WebServlet("/session3")
  9. public class SessionServlet3 extends HttpServlet {
  10.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  12.     }
  14.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.         HttpSession session = request.getSession();
  16.         session.setAttribute("username", "sssss");
  17.         Cookie cookie = new Cookie("JSESSIONID", session.getId());
  18.         cookie.setMaxAge(180);
  19.         response.addCookie(cookie);
  20.     }
  21. }
  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import javax.servlet.http.HttpSession;
  9. import java.io.IOException;
  11. @WebServlet("/session4")
  12. public class SessionServlet4 extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         HttpSession session = request.getSession();
  19.         String username = (String) session.getAttribute("username");
  20.         System.out.println(username);
  21.     }
  22. }

session域

Context、Request、Session

Context > Session > Request

使用：

Context域：范围最大的一个域。和用户无关的。所以可以用来存放一些和用户无关的，所有用户都相同的数据，比如商城的商品分类

Session域：可以用来存放用户相关的数据。比如用户的购物车数据、用户的浏览记录、用户名等

Request域：非常的小，如果希望在一次请求中用到该数据，那么就可以使用request域，让转发的两个组件之间进行共享该数据。

session的生命周期

创建：对象的创建（request.getSession()）

销毁：对象的销毁（应用被卸载、服务器关闭）

数据赋值：setAttribute、getAttribute、removeAttribute

对象的销毁并不意味着数据的销毁，如果希望数据销毁只有两种方式：

1.主动调用session.invalidate();

2.session默认有效期到达，session也会失效 如果30min内没有访问当前session，那么session失效，如果在30min内访问了一次session，那么重新开始计时

  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  10. @WebServlet("/login")
  11. public class LoginServlet extends HttpServlet {
  12.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  13.         response.setContentType("text/html;charset=utf-8");
  14.         String username = request.getParameter("username");
  15.         String password = request.getParameter("password");
  16.         request.getSession().setAttribute("username", username);
  17.         response.getWriter().println("登录成功，跳转中......");
  18.         response.setHeader("refresh", "2;url=" + request.getContextPath() + "/info");
  20.     }
  22.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  24.     }
  25. }
  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  10. @WebServlet("/info")
  11. public class InfoServlet extends HttpServlet {
  12.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  14.     }
  16.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  17.         response.setContentType("text/html;charset=utf-8");
  18.         String username = (String) request.getSession().getAttribute("username");
  19.         response.getWriter().println("欢迎您 " + username + "<a href='" + request.getContextPath() + "/logout" + "'>点我注销</a>");
  20.     }
  21. }
  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  10. @WebServlet("/logout")
  11. public class LogoutServlet extends HttpServlet {
  12.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  14.     }
  16.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  17.         //注销的逻辑应该怎么写？
  18.         request.getSession().invalidate();
  19.     }
  20. }

重构到一个servlet中。因为我们发现这些servlet都是在说用户相关，所以可以放到一个servlet中。

  1. package com.cskaoyan.session;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  10. @WebServlet("/user")
  11. public class UserServlet extends HttpServlet {
  12.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  13.         String op = request.getParameter("op");
  14.         if("login".equals(op)){
  15.             login(request, response);
  16.         }
  17.     }
  19.     private void login(HttpServletRequest request, HttpServletResponse response) throws IOException {
  20.         response.setContentType("text/html;charset=utf-8");
  21.         String username = request.getParameter("username");
  22.         String password = request.getParameter("password");
  23.         request.getSession().setAttribute("username", username);
  24.         response.getWriter().println("登录成功，跳转中......");
  25.         response.setHeader("refresh", "2;url=" + request.getContextPath() + "/user?op=info");
  27.     }
  29.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  30.         String op = request.getParameter("op");
  31.         if("info".equals(op)){
  32.             info(request, response);
  33.         }else if("logout".equals(op)){
  34.             logout(request, response);
  35.         }
  36.     }
  38.     private void logout(HttpServletRequest request, HttpServletResponse response) {
  39.         request.getSession().invalidate();
  40.         //跳转
  41.     }
  43.     private void info(HttpServletRequest request, HttpServletResponse response) throws IOException {
  44.         response.setContentType("text/html;charset=utf-8");
  45.         String username = (String) request.getSession().getAttribute("username");
  46.         response.getWriter().println("欢迎您 " + username + "<a href='" + request.getContextPath() + "/user?op=logout" + "'>点我注销</a>");
  48.     }
  49. }

购物车案例

  1. package com.cskaoyan.cart;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  9. import java.util.ArrayList;
  10. import java.util.List;
  12. @WebServlet(value = "/index",loadOnStartup = 1)
  13. public class IndexServlet extends HttpServlet {
  15.     @Override
  16.     public void init() throws ServletException {
  17.         //初始化商品信息
  18.         Product iphone12 = new Product("1", "iphone12", 6999.0);
  19.         Product mate40 = new Product("2", "huawei mate40", 6699.0);
  20.         Product product = new Product("3", "mi 11 pro", 5999.0);
  21.         List<Product> products = new ArrayList<>();
  22.         products.add(iphone12);
  23.         products.add(mate40);
  24.         products.add(product);
  25.         getServletContext().setAttribute("products", products);
  26.     }
  28.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  30.     }
  32.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  33.         //初始化商品信息
  34.         List<Product> products = (List<Product>) getServletContext().getAttribute("products");
  35.         for (Product product : products) {
  36.             response.getWriter().println("<a href='" + request.getContextPath() + "/detail?id=" + product.getId() + "'>" + product.getName() +"</a>");
  37.         }
  38.     }
  39. }
  1. package com.cskaoyan.cart;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  9. import java.util.List;
  11. @WebServlet("/detail")
  12. public class DetailServlet extends HttpServlet {
  13.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  15.     }
  17.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  18.         response.setContentType("text/html;charset=utf-8");
  19.         String id = request.getParameter("id");
  20.         if(id == null || id.isEmpty()){
  21.             response.getWriter().println("invalid parameter");
  22.             return;
  23.         }
  24.         response.getWriter().println("<!DOCTYPE html>\n" +
  25.                 "<html lang=\"en\">\n" +
  26.                 "<head>\n" +
  27.                 "    <meta charset=\"UTF-8\">\n" +
  28.                 "    <title>Title</title>\n" +
  29.                 "</head>\n" +
  30.                 "<body>");
  31.         List<Product> products = (List<Product>) getServletContext().getAttribute("products");
  32.         for (Product product : products) {
  33.             if(product.getId().equals(id)){
  34.                 response.getWriter().println(product);
  35.             }
  36.         }
  39.         String index = request.getContextPath() + "/index";
  40.         String addCart = request.getContextPath() + "/addCart?id=" + id;
  41.         String viewCart = request.getContextPath() + "/viewCart";
  42.         response.getWriter().println("<a href='" + index + "'>返回首页</a>");
  43.         response.getWriter().println("<a href='" + addCart + "'>加入购物车</a>");
  44.         response.getWriter().println("<a href='" + viewCart + "'>查看购物车</a>");
  46.         response.getWriter().println("</body>\n" +
  47.                 "</html>");
  48.     }
  49. }
  1. package com.cskaoyan.cart;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import javax.servlet.http.HttpSession;
  9. import java.io.IOException;
  10. import java.util.List;
  12. @WebServlet("/viewCart")
  13. public class ViewCartServlet extends HttpServlet {
  14.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  16.     }
  18.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  19.         response.setContentType("text/html;charset=utf-8");
  20.         HttpSession session = request.getSession();
  21.         List<String> cart = (List<String>) session.getAttribute("cart");
  22.         if(cart == null){
  23.             response.getWriter().println("购物车为空，去选购吧.....");
  24.             String index = request.getContextPath() + "/index";
  25.             response.setHeader("refresh", "2;url=" + index);
  26.             return;
  27.         }
  28.         List<Product> products = (List<Product>) getServletContext().getAttribute("products");
  29.         for (Product product : products) {
  30.             for (String id : cart) {
  31.                 if(id.equals(product.getId())){
  32.                     response.getWriter().println(product);
  33.                 }
  34.             }
  35.         }
  36.         String index = request.getContextPath() + "/index";
  37.         response.getWriter().println("<a href='" + index + "'>返回首页</a>");
  40.     }
  41. }
  1. package com.cskaoyan.cart;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.annotation.WebServlet;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import javax.servlet.http.HttpSession;
  9. import java.io.IOException;
  10. import java.util.ArrayList;
  11. import java.util.List;
  13. @WebServlet("/addCart")
  14. public class AddCartServlet extends HttpServlet {
  15.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  17.     }
  19.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  20.         response.setContentType("text/html;charset=utf-8");
  21.         String id = request.getParameter("id");
  22.         if(id == null || id.isEmpty()){
  23.             response.getWriter().println("invalid parameter");
  24.             return;
  25.         }
  26.         HttpSession session = request.getSession();
  27.         List<String> cart = (List<String>) session.getAttribute("cart");
  28.         if(cart == null){
  29.             cart = new ArrayList<>();
  30.             session.setAttribute("cart", cart);
  31.         }
  32.         cart.add(id);
  33.         response.getWriter().println("添加到购物车成功....");
  34.         String index = request.getContextPath() + "/index";
  35.         response.setHeader("refresh", "2;url=" + index);
  37. //        List<String> list = new ArrayList<>();
  38. //        list.add(id);
  39.         //不能用set，因为永远只有一个 session.setAttribute("id", id);
  40.     }
  41. }
  1. package com.cskaoyan.cart;
  3. public class Product {
  5.     private String id;
  7.     private String name;
  9.     private Double price;
  11.     public String getId() {
  12.         return id;
  13.     }
  15.     public void setId(String id) {
  16.         this.id = id;
  17.     }
  19.     public String getName() {
  20.         return name;
  21.     }
  23.     public void setName(String name) {
  24.         this.name = name;
  25.     }
  27.     public Double getPrice() {
  28.         return price;
  29.     }
  32.     public void setPrice(Double price) {
  33.         this.price = price;
  34.     }
  36.     public Product(String id, String name, Double price) {
  37.         this.id = id;
  38.         this.name = name;
  39.         this.price = price;
  40.     }
  42.     public Product() {
  43.     }
  45.     @Override
  46.     public String toString() {
  47.         return "Product{" +
  48.                 "id='" + id + '\'' +
  49.                 ", name='" + name + '\'' +
  50.                 ", price=" + price +
  51.                 '}';
  52.     }
  53. }

session依赖于cookie，如果cookie禁用会怎么样

EE规范提供了一个URL重写方法，此时JSESSIONID会附着在地址栏的后面

今晚可以做的

1.提到了数量问题

2.实现历史足迹。