实现购物车的Session

                        [图-1]整体结构图

package cn.itcast;import java.io.IOException;
import java.io.PrintWriter;
import java.util.Collection;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;/*** Servlet implementation class ListBookServlet*/
public class ListBookServlet extends HttpServlet {private static final long serialVersionUID = 1L;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//设置中文编码。response.setContentType ( "text/html;charset=utf-8");//提示PrintWriter out = response.getWriter();Collection<Book> books = BookDB.getAll();out.write("本站提供的图书有:<br />");//把数目列出来for (Book book : books){String url = "/chapter5/PurchaseServlet?id=" + book. getId ();System.out.println(url);//地址是/chapter5/PurchaseServlet?id=1out.write (book.getName ()+ "<a href='"+ url+"'>点击购买</a><br />");}}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)*/protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubdoGet(request, response);}}

package cn.itcast;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;/*** Servlet implementation class CartServlet*/
public class CartServlet extends HttpServlet {private static final long serialVersionUID = 1L;/*** @see HttpServlet#HttpServlet()*/public CartServlet() {super();// TODO Auto-generated constructor stub}/*** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)*/protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.setContentType("text/html;charset=utf-8");PrintWriter out=response.getWriter();List<Book> cart=null;boolean purFlag=true;HttpSession session=request.getSession(false);if(session==null){purFlag=false;}else{cart=(List) session.getAttribute("cart");if(cart==null){purFlag=false;}}//页面展示if(!purFlag){out.write("对不起");}else{out.write("您购买的书有");double price=0;for(Book book:cart) {out.write(book.getName());}}}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)*/protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubdoGet(request, response);}}

package cn.itcast;import java.io.IOException;
import java.util.ArrayList;
import java.util.List;import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;/*** Servlet implementation class PurchaseServlet*/
public class PurchaseServlet extends HttpServlet {private static final long serialVersionUID = 1L;/*** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse*      response)*/protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//设置一个ID接受量String id=request.getParameter("id");//id没有，就到数目列表页面if(id==null){String url="/chapter5/ListBookServlet";response.sendRedirect(url);return ;}Book book =BookDB.getBook(id);//创建或者获得session对象HttpSession session =request.getSession();//从session中获得购物车List<Book> cart=(List) session.getAttribute("cart");//创建购物车if(cart==null){//首次购买，创建一个购物车cart=new ArrayList<Book>();//将购物车存入session对象session.setAttribute("cart", cart);}//将商品放入购物车cart.add(book);//创建cookie存放session的标识符Cookie cookie =new Cookie("jsess",session.getId());System.out.println(session.getId());cookie.setMaxAge(60*30);cookie.setPath("/chapter5");response.addCookie(cookie);//重定向到购物车界面String url="/chapter5/CartServlet";response.sendRedirect(url);}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)*/protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubdoGet(request, response);}}

Session创建的时候会返回一个存放此session的id的cookie给浏览器保存在缓存中。
session id会由服务器端写入到cookie中，后期访问服务器端会以此id为标识。cookie失效时间可以服务器端自己设置。

案例中又手动创建了一个Cookie所以又两个Cookie

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