JavaWeb学习-会话管理系列-6-cookie练习-浏览历史记录

ゝ一纸荒年。 2022-01-30 15:29 207阅读 0赞

本篇继续来做一个cookie的经典练习场景，如何显示用户浏览器网站上的商品的历史纪录。这个功能很多购物网站上都有，我们来模拟这个场景的实现过程。例如一个卖书的网站，我们定义这个网站有4本书，然后我们历史纪录只显示用户最近浏览的三本书，当然也可能用户只浏览了一本，两本或者没有一本书，这些场景都需要考虑。

需求场景

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70][]

上面就是用户第一次打开这个卖书网站，这个时候没有浏览任何一本书详情页，所以没有cookie也就没有历史纪录。下面点击四本书任何一本，跳转到详情页。

![20190520140218725.png][]

返回带主页

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70 1][]

1.项目结构

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70 2][]

web.xml

<?xml version="1.0" encoding="UTF-8"?>
 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
 
 <servlet>
 <servlet-name>showAllBooksServlet</servlet-name>
 <servlet-class>com.anthony.history.ShowAllBooksServlet</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>showAllBooksServlet</servlet-name>
 <url-pattern>/cookie/showAllBook</url-pattern>
 </servlet-mapping>
 
 <servlet>
 <servlet-name>showBookDetail</servlet-name>
 <servlet-class>com.anthony.history.ShowBookDetail</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>showBookDetail</servlet-name>
 <url-pattern>/cookie/showBookDetail</url-pattern>
 </servlet-mapping>
 
 <welcome-file-list>
 <welcome-file>index.html</welcome-file>
 <welcome-file>index.htm</welcome-file>
 <welcome-file>index.jsp</welcome-file>
 <welcome-file>default.html</welcome-file>
 <welcome-file>default.htm</welcome-file>
 <welcome-file>default.jsp</welcome-file>
 </welcome-file-list>
 </web-app>

Book.java

package com.anthony.entity;
    
    public class Book {
    	private String id;
    	private String name;
    	private double price;
    	private String author;
    	
    	public Book(String id, String name, double price, String author) {
    		super();
    		this.id = id;
    		this.name = name;
    		this.price = price;
    		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 double getPrice() {
    		return price;
    	}
    	public void setPrice(double price) {
    		this.price = price;
    	}
    	public String getAuthor() {
    		return author;
    	}
    	public void setAuthor(String author) {
    		this.author = author;
    	}
    	@Override
    	public String toString() {
    		return "Book [id=" + id + ", name=" + name + ", price=" + price + ", author=" + author + "]";
    	}
    	
    }

DBUtil.java

package com.anthony.util;
 
 import java.util.HashMap;
 import java.util.Map;
 
 import com.anthony.entity.Book;
 
 public class DBUtil {
 	
 	private static Map<String, Book> books = new HashMap<String, Book>();
 	
 	//这里不走数据库查询，直接生成几本书来模拟下
 	static {
 		books.put("1", new Book("1", "西游记", 16.9, "吴承恩"));
 		books.put("2", new Book("2", "红楼梦", 37.3, "曹雪芹"));
 		books.put("3", new Book("3", "三国演义", 25.8, "罗贯中"));
 		books.put("4", new Book("4", "水浒传", 33.0, "施耐庵"));
 	}
 	
 	//得到所有图书
 	public static Map<String, Book> findAllBooks() {
 		return books;
 	}	
 	
 	//根据id查找到书
 	public static Book findBookById(String id) {
 		return books.get(id);
 	}
 }

com.anthony.history.ShowAllBooksServlet.java

package com.anthony.history;
 
 import java.io.IOException;
 import java.io.PrintWriter;
 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;
 
 import com.anthony.entity.Book;
 import com.anthony.util.DBUtil;
 
 public class ShowAllBooksServlet extends HttpServlet {
 
 	@Override
 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 		resp.setContentType("text/html;charset=UTF-8");
 		PrintWriter out = resp.getWriter();
 		out.write("本网站有以下好书： ");
 		Map<String, Book> books = DBUtil.findAllBooks();
 		for (Map.Entry<String, Book> b : books.entrySet()) {
 			out.write("<a href='"+req.getContextPath()+"/cookie/showBookDetail?id="+b.getKey()+" ' target='_blank'>"+b.getValue().getName()+"</a> ");
 		}
 		
 		out.write("<hr/>你最近浏览过的书有： ");
 		//拿到cookie
 		Cookie[] cookies = req.getCookies();
 		for (int i = 0; cookies != null && i < cookies.length; i++) {
 			if("bookHistoryId".equals(cookies[i].getName())) {
 				String value = cookies[i].getValue();
 				String[] ids = value.split("-"); //切割 然后遍历
 				for (int j = 0; j < ids.length; j++) {
 					//根据id查找书
 					Book book = DBUtil.findBookById(ids[j]);
 					//out.print(book.getName() + " ");
 					out.write("<a href='"+req.getContextPath()+"/cookie/showBookDetail?id=" + book.getId()+" ' target='_blank'>" + book.getName()+"</a> ");
 				}
 			}
 		}
 	}
 
 	@Override
 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 		doGet(req, resp);
 	}
 
 }

com.anthony.history.ShowBookDetail.java

package com.anthony.history;
 
 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;
 
 import com.anthony.entity.Book;
 import com.anthony.util.DBUtil;
 
 public class ShowBookDetail extends HttpServlet {
 	
 	@Override
 	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 		resp.setContentType("text/html;charset=UTF-8");
 		PrintWriter out = resp.getWriter();
 		//显示图书的详细信息
 		
 		//获得id
 		String id = req.getParameter("id");
 		Book book = DBUtil.findBookById(id);
 		out.print(book);
 		//把当前浏览过书的ID写到cookie(客户端)
 		String bookHistoryId = organizeId( id, req);
 		Cookie ck = new Cookie("bookHistoryId", bookHistoryId);
 		ck.setPath("/");
 		ck.setMaxAge(Integer.MAX_VALUE);// 一直保存
 		resp.addCookie(ck);
 		
 	}
 	
 	private String organizeId(String id, HttpServletRequest req) {
 		//拿到cookie
 		Cookie[] cookies = req.getCookies();
 		if(cookies == null) {
 			return id; //第一次请求时没有cookie
 		}
 		//判断cookie数组中有没有叫做historyBookId的cookie
 		Cookie historyBookId = null;
 		for (int i = 0; i < cookies.length; i++) {
 			if("bookHistoryId".equals(cookies[i].getName())) {
 				historyBookId = cookies[i];
 			}
 		}
 		//如果没有想要的cookie
 		if(historyBookId == null) {
 			return id;
 		}
 		
 		String value = historyBookId.getValue(); //得到可能时 2-1-3这样字符串
 		String[] values = value.split("-"); //切割拿到全部id
 		LinkedList<String> list = new LinkedList<String>(Arrays.asList(values));
 		
 		//这里我们模拟历史纪录只能存3本书的场景
 		if(list.size() < 3) { // 1-2
 			if(list.contains(id)) {
 				list.remove(id); // 如果 1-2 中包含2， 那么就删除2
 			}
 		}else { //三本数
 			if(list.contains(id)) {
 				list.remove(id);// 从3本书中删除id对应这本，后面还会添加回来
 			}else {
 				list.removeLast(); //删除最后一本，后面会添加id新纪录进去
 			}
 			
 		}
 		list.addFirst(id); // 62行删除的id，这行会加回来，这样浏览先后顺序就对了
 		
 		//从浏览先后顺序倒叙输出三本书ID
 		StringBuffer sb = new StringBuffer();
 		for (int i = 0; i < list.size(); i++) {
 			if( i > 0) {
 				sb.append("-"); // 1-2-3
 			}
 			sb.append(list.get(i));
 		}
 		
 		return sb.toString();
 	}
 
 	@Override
 	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 		doGet(req,resp);
 	}
 }

启动tomcat，部署代码，就可以看到需求描述的场景。

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[20190520140218725.png]: /images/20220130/0ebf52d6a9d646a79a71c8c69f458f3b.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70 1]: /images/20220130/61f2332b12fc47afaa1af389635e8647.png
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