cookie02--回显浏览过的商品

1.

package cn.itcast.cookie;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.LinkedHashMap;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//代表首页的servlet
public class CookieDemo3 extends HttpServlet {
	
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//1. 输出网站所有的商品
		request.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		PrintWriter writer = response.getWriter();
		writer.write("本网站有如下商品:<br/>"); // 浏览器换行用br,java用/r/n
		
		//1.2 从DB中获取所有的商品信息
		Map<String, Book> map = DB.getAll();
		for(Map.Entry<String, Book> entry : map.entrySet()){
			Book book = entry.getValue();
			writer.print("<a href='/day07/CookieDemo4?id="+ book.getId() +" ' target='_blank'>"+  book.getName() +"</a><br/>");
		}
		
		//2.显示用户曾经看过的商品
		writer.print("<br/>您曾经浏览过的商品: <br/>");
		Cookie[] cookies = request.getCookies();
		
		for(int i = 0; cookies != null && i < cookies.length; i++){
			if (cookies[i].getName().equals("bookHistory")) {
				String[] ids = cookies[i].getValue().split("\,"); //推荐转意
				for( String id : ids) { // 通过id去db中查找对应的书
					Book book = DB.getAll().get(id);
					writer.print(book.getName() + "<br/>");
				}
			}
		}
	}
	
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException ,IOException {
		
		this.doGet(request, response);
	}

}

class DB{
	//想存的数据的顺序与显示的顺序一致,用LinkedHashMap
	private static Map<String, Book> map = new LinkedHashMap<String, Book>(); 
	
	static{ //静态代码块确保只加载一次
		map.put("1", new Book("1", "javaweb开发", "老张", "高薪书"));
		map.put("2", new Book("2", "andorid开发", "老张", "高薪书"));
		map.put("3", new Book("3", "ios开发", "老张", "高薪书"));
		map.put("4", new Book("4", "javaEE开发", "老张", "高薪书"));
		map.put("5", new Book("5", "疯狂的java开发", "老张", "高薪书"));
	}
	
	public static Map<String, Book> getAll(){
		return map;
	}
}


class Book{
	
	private String id;
	private String name;
	private String author;
	private String description;
	
	public Book(){}

	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;
	}
	
	
	
}

　　2.

package cn.itcast.cookie;


import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.LinkedList;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CookieDemo4 extends HttpServlet {
	
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		
		//根据用户传过来的id,显示相应商品的详细信息
		String id = request.getParameter("id");
		Book book = DB.getAll().get(id);
		out.write(book.getId() + "<br/>");
		out.write(book.getName() + "<br/>");
		out.write(book.getAuthor() + "<br/>");
		out.write(book.getDescription() + "<br/>");
		
		//构建cookie, 回写给浏览器
		String cookieValue = buildCookie(id, request);
		Cookie cookie = new Cookie("bookHistory", cookieValue);
		cookie.setMaxAge(3600*24*30);
		cookie.setPath(request.getContextPath());
		response.addCookie(cookie);
	}

	private String buildCookie(String id, HttpServletRequest request) {
		//bookHistory = null   1    1
		//bookHistory = 2,5,1   1    1,2,5
		//bookHistory = 2,5,4   1    1,2,5
		//bookHistory = 2,5     1    1,2,5
		
		Cookie[] cookies = request.getCookies();
		String bookHistory = null;
		for(int i = 0; cookies != null && i < cookies.length; i++) {
			if(cookies[i].getName().equals("bookHistory")){
				bookHistory = cookies[i].getValue();
			}
		}
		if(bookHistory == null){ //第一次
			return id;
		}
		
		LinkedList<String> list = new LinkedList<String>(Arrays.asList(bookHistory.split("\,")));
		/*if(list.contains(id)){ //当前浏览的商品在cookie中存在
			list.remove(id); //把存在的删除
			list.addFirst(id);//把当前的放在第一个
		} else{ //不存在; 
			if(list.size() >= 3){// 如何list满了把当前的放在第一个并删除最后一个
				list.removeLast();
				list.addFirst(id);
			} else{ //直接添加到list头部
				list.addFirst(id);
			}
		}*/
		
		if(list.contains(id)){ 
			list.remove(id);
		} else{ 
			if(list.size() >= 3){
				list.removeLast();
			} 
		}
		list.addFirst(id);
		
		StringBuilder sb = new StringBuilder();
		for(String bookId : list) {
			sb.append(bookId).append(",");
		}
		sb.deleteCharAt(sb.length() - 1);
		bookHistory = sb.toString();

		return bookHistory;
	}

}