servlet显示商品浏览历史记录

矫情吗；* 2022-08-12 01:19 203阅读 0赞

假设有一个数据库和书本对象

//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;
    	}
    	
    }

第一个servlet显示商品列表和历史记录

第二个servlet显示商品具体信息，存储cookie

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");
    				
    		//显示商品信息
    		PrintWriter out = response.getWriter();
    		
    		//根据用户带来的id显示商品信息
    		String id = request.getParameter("id");
    		Book book = (Book) Db.getAll().get(id);
    		out.print(book.getId()+"<br>");
    		out.print(book.getName()+"<br>");
    		out.print(book.getAuthor()+"<br>");
    		
    		//构建Cookie回写给浏览器
    		String cookieValue = buildCookie(id,request);
    		Cookie cookie = new Cookie("bookHistory", cookieValue);
    		cookie.setPath("/day07");
    		cookie.setMaxAge(3600*24);
    		response.addCookie(cookie);
    	}
    
    	
    	private String buildCookie(String id, HttpServletRequest request) {
    		
    		String bookHistory = null;
    		Cookie cookies[] = request.getCookies();
    		for(int i=0; cookies!=null&&i<cookies.length; i++){
    			if(cookies[i].getName().equals("bookHistory")){
    				bookHistory = cookies[i].getValue();
    			}
    		}
    		
    		/*分情况谈论 
    		 * old   id   now
    		 * null  1    1
    		 * 2,3   1 	  1,2,3
    		 * 1      1   1
    		 *  ...
    		 */
    		if(bookHistory==null){
    			return id;
    		}
    		
    		//LinkedList便于增删改查
    		LinkedList list = new LinkedList(Arrays.asList(bookHistory.split("\\,")));
    		if(list.contains(id)){
    			list.remove(id);
    			list.addFirst(id);
    		}else{
    			if(list.size()>=3){
    				list.removeLast();
    				list.addFirst(id);
    			}else{
    				list.addFirst(id);
    			}
    		}
    		
    		StringBuilder sb = new StringBuilder();
    		for(Object ob : list){
    			sb.append(ob+",");
    		}
    		
    		return sb.deleteCharAt(sb.length()-1).toString();
    	}