用session实现简单的购物

大型的购物网站，都是使用cookie,因为cookie是存在浏览器端。session是存在服务器端，对服务器的压力较大。

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package shopsession;

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;

public class ListBookServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter pw = response.getWriter();
request.getSession();
pw.print("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("/servletdemo/servlet/Buyservlet?id=" + book.getId());
pw.print(book.getName()
+ "<a href='"+url+"' target=_blank'>购买</a><br/>");
}
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}

}

class Db {
private static Map<String, Book> map = new LinkedHashMap();
static {
map.put("1", new Book("1", "java开发", "战三", "报错的书籍"));
map.put("2", new Book("2", "servlet开发", "李四", "破玩意"));
map.put("3", new Book("3", "web开发", "万物", "没有评价"));
map.put("4", new Book("4", "appium开发", "麻子", "一阿班一阿班"));
map.put("5", new Book("5", "ios开发", "哈哈", "还好吧"));
}

public static Map getAll() {
return map;

}
}

class Book implements Serializable {
private String id;
private String name;
private String author;
private String description;

public Book() {
super();
}

public Book(String id, String name, String author, String description) {
super();
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;
}

}

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package shopsession;

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;

public class Buyservlet extends HttpServlet {
//完成购买
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String id=request.getParameter("id");
Book book=(Book) Db.getAll().get(id);
HttpSession session= request.getSession(false);
//手工发sessionid.解决关闭浏览器之后上次买的东西还在。

//从session得到用户用于保存所有书的集合（购物车）
List list=(List) session.getAttribute("list");
if(list==null){
list=new ArrayList();
session.setAttribute("list", list);
}
list.add(book);
//重定向
String url=response.encodeRedirectURL(request.getContextPath()+"/servlet/ListCartServlet");
response.sendRedirect(url);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}

}

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package shopsession;

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;
//显示用户购买的商品
public class ListCartServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter pw=response.getWriter();
HttpSession session=request.getSession(false);
if(session==null){
pw.write("您没有购买任何商品+<br/>");
return;
}

pw.write("您购买的商品如下+<br/>");
List<Book> list=(List) session.getAttribute("list");

for(Book book:list){
pw.write(book.getName());
}
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}

}