学步园

j假设一个数据库和书对象

//数据库
class Db{
	private static Map<String, Book> map = new LinkedHashMap();
	
	static{
		map.put("1", new Book("1","web开发","老张"));
		map.put("2", new Book("2","spring","老毕"));
		map.put("3", new Book("3","struts","老张"));
		map.put("4", new Book("4","jdbc","老黎"));
	}
	
	//拿到书
	public static Map getAll(){
		return map;
	}
}

//书对象
class Book{
	private String id;
	private String name;
	private String author;
	
	public Book() {
		super();
	}

	public Book(String id, String name, String author) {
		super();
		this.id = id;
		this.name = name;
		this.author = author;
	}
	
	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;
	}
	
}

将书的列表显示出来

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//设置防止乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		out.write("本网站有如下商品：<br>");
		
		request.getSession();
		
		Map<String,Book> map = Db.getAll();
		for(Map.Entry<String,Book> entry : map.entrySet()){
			Book book = entry.getValue();
			
			//重写url防止用户禁用cookie
			String url = response.encodeURL("BuyServlet?id="+book.getId());
			out.write(book.getName()+"<a href='"+url+"' target='_blank'>购买</a><br>");
		}
	}

点击购买后

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String id = request.getParameter("id");
		
		//根据id号找到书
		Map<String, Book> map = Db.getAll();
		Book book = map.get(id);
		
		HttpSession session = request.getSession(false);
		
		//从session得到书,使用list存放
		List list = (List) session.getAttribute("list");
		if(list==null){
			list = new ArrayList();
			session.setAttribute("list", list);
		}
		list.add(book);
		
		//重写url
		String url = response.encodeRedirectURL("/day07/ListCartServlet");
		response.sendRedirect(url);
	}

最后显示购买的界面

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		//设置防止乱码
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		//由session得到书目
		HttpSession session = request.getSession(false);
		
		
		//对session进行判断
		if(session==null){
			out.write("you do not hava to purchase any goods<br>");
			return;
		}
		
		out.write("You purchase the following commodity: <br>");
		List<Book> list = (List) session.getAttribute("list");
		for(Book book : list){
			out.write(book.getName()+"<br>");
		}
	}