Session案例，显示商品浏览记录

相对于Cookie而言，Session并不经常在服务器中使用，因为session为每一个浏览器用户创建了一个session，这样对服务器的要求无形之中高了很多，而cookie是对每个浏览器发送数据，所以服务器负担小，所以大部分浏览器还是选择使用cookie来实现浏览记录的显示。

当用户的浏览器禁用Cookie的时候，可以使用超链接里面带着指定的id去访问servlet，具体代码为response.encodeURL("/");里面放具体的servlet访问地址,这样的话，就能带着指定的id去访问从而解决了禁用cookie问题,
如果用户没有禁用cookie，则第一次他会将超链接和cookie同时发送回去，但是，当第二次访问的时候，服务器发现他返回了cookie,则就不在重新写超链接了

本案例是使用session来实现模仿当用户在首页点击了商品名字的时候，通过session记录了各个他点击的商品的名字，然后当选择结账的时候，自动将他选择购买的商品显示出来，下面上代码

第一段代码是用来充当首页的servlet,里面假设了如果用户禁用cookie的情况

package com.bird.shopping;import java.io.IOException;import java.io.PrintWriter;import java.io.Serializable;import java.util.LinkedHashMap;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * @category 模拟网站首页的servlet用来显示所有的商品 * @author Bird * */public class ListBookServlet extends HttpServlet {private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();request.getSession();//注意，一定要得到session，否则无法进行自动的id添加out.write("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 = entry.getValue();String url = response.encodeURL("/Web/servlet/BuyServlet?id="+book.getId()+"");out.write(book.getName()+"<a href='"+url+"' target='_blank'>购买</a></br>");}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {}}class DB{//必须使用链表Map进行有序存储private static Map<String,Book> map = new LinkedHashMap<String,Book>();static{map.put("1", new Book("1","javaweb开发详解","老张","一本好书!!!"));map.put("2", new Book("2","jdbc开发详解","老张","一本好书!!!"));map.put("3", new Book("3","sping开发详解","老黎","一本好书!!!"));map.put("4", new Book("4","struts开发详解","老宇","一本好书!!!"));map.put("5", new Book("5","heibrate开发详解","老毕","一本好书!!!"));}public static Map<String,Book> getAll(){return map;}}class Book implements Serializable{private static final long serialVersionUID = 1L;private String id;private String name;private String author;private String description;public Book(){}public Book(String id, String name, String author, String description) {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;}}

第二段代码，是根据带过来的id将对应的商品名称放入到session中，以备下面的结账，当然，最终的跳转一定要使用浏览器的本地重定向，而不是服务器的请求重定向，否则会反复访问这个servlet干同样的事情，导致多次的购买

package com.bird.shopping;import java.io.IOException;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * @category 购买 * @author Bird * */public class BuyServlet extends HttpServlet {private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String id = request.getParameter("id");Book book = DB.getAll().get(id);HttpSession session = request.getSession();//从session获得用户保存的数据（购物车）@SuppressWarnings("unchecked")List<Book> list = (List<Book>) session.getAttribute("list");if(list==null){list = new ArrayList<Book>();session.setAttribute("list", list);}list.add(book);String url = response.encodeRedirectURL(request.getContextPath()+"/servlet/ListCarServlet");//request.getRequestDispatcher("/servlet/ListCarServlet").forward(request, response);response.sendRedirect(url);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {}}

第三段代码，用来显示已经购买的商品名称

package com.bird.shopping;import java.io.IOException;import java.io.PrintWriter;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * @category 显示用户购买的商品 * @author Bird * */public class ListCarServlet extends HttpServlet {private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();HttpSession session = request.getSession();if(session == null){out.write("您没有购买任何商品");return;}out.write("您购买了如下商品:</br>");@SuppressWarnings("unchecked")List<Book> list = (List<Book>) session.getAttribute("list");for(Book book: list){out.write(book.getName());out.write("</br>");}}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {}}