javaweb之Cookie显示商品的浏览记录和Cookie的常见应用有哪些

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 {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 1.显示网站的所有商品
response.setCharacterEncoding("UTF-8");
response.setHeader("Content-type", "text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.print("本网站有如下商品：<br/>");
Map<String, Book> map = Db.getAll();
// 遍历存有数据信息的“数据库”显示到页面中
for (Map.Entry<String, Book> entry : map.entrySet()) {
Book book = entry.getValue();
// 点击超链接后，在新的页面打开target="_blank"
out.print("<a href='/day07/servlet/CookieDemo4?id=" + book.getId()
+ "' target='_blank'>" + book.getName() + "</a><br/>");
}

// 2.显示用户曾经看过的商品
out.print("<br/>您曾经看过如下商品：</br>");
// 拿到请求中所有的Cookie
Cookie cookies[] = request.getCookies();
// 遍历Cookie，看看有没有浏览商品的Cookie
for (int i = 0; cookies != null && i < cookies.length; i++) {
// 如果有浏览商品的Cookie则拿到其中的商品，浏览过的商品是很多件的，商品是以,分割的
if (cookies[i].getName().equals("bookHistory")) {
// 分割字符串，拿到留有浏览过的商品的id
// 不管,有没有在正则表达式中定义，都以,分割
String[] ids = cookies[i].getValue().split("\\,"); // 2,3,1
// 遍历所有商品id获得商品
for (String id : ids) {
Book book = Db.getAll().get(id);
out.print(book.getName() + "<br />");
}
}
}
}

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

}

// 模拟数据库，从这个类中提取书的信息
class Db {
// 实际开发中存储数据的集合有检索数据的需求，都用双列的（map），如果没有检索数据需求，用单列的（list、set）
// LinkedHashMap是有序存储
private static Map<String, Book> map = new LinkedHashMap<String, Book>();
// 对书进行静态初始化
static {
// key是商品的id，value是商品，商品中也是有商品的id的
map.put("1", new Book("1", "javaweb开发", "老张", "一本好书！"));
map.put("2", new Book("2", "jdbc开发", "老张", "一本好书！"));
map.put("3", new Book("3", "spring开发", "老黎", "一本好书！"));
map.put("4", new Book("4", "struts开发", "老毕", "一本好书！"));
map.put("5", new Book("5", "android开发", "老黎", "一本好书！"));
}

public static Map<String, Book> getAll() {
return map;
}
}

// 模拟书类
class Book {
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;
}
}

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;

//显示商品详细信息的servlet
public class CookieDemo4 extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 1.根据用户带过来的id，显示相应商品的详细信息
response.setCharacterEncoding("UTF-8");
response.setHeader("Content-type", "text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
// 获取浏览的书的id
String id = request.getParameter("id");
// 根据id拿到书的信息
Book book = Db.getAll().get(id);
out.print(book.getId() + "<br/>");
out.print(book.getAuthor() + "<br/>");
out.print(book.getName() + "<br/>");
out.print(book.getDescription() + "<br/>");

// 2.构建Cookie，回写给浏览器
String cookieValue = buildCookie(id, request);

Cookie cookie = new Cookie("bookHistory", cookieValue);
cookie.setMaxAge(1 * 3600 * 24 * 30);
cookie.setPath("/day07");
response.addCookie(cookie);
}

// 构建Cookie的方法
private String buildCookie(String id, HttpServletRequest request) {
// 1.用户没有带Cookie过来 bookHistory=null id=1 return 1
// 2.用户带Cookie过来 bookHistory=2,5,1 id=1 bookHistory中包含id
// 要把2,5,1中的1删掉加在最前面 return1,2,5
// 3.用户带Cookie过来 bookHistory=2,5,4 id=1 假设列表最大显示3个Cookie return1,2,5
// 4.用户带Cookie过来 bookHistory=2,5 id=1 并且列表没有超出范围 return 1,2,5

// 先把要Cookie的值创建出来
String bookHistory = null;
// 得到Cookie，看看有没有bookHistory这个Cookie，有的话，把它的值赋给bookHistory（要返回的String类型的）
Cookie[] cookies = request.getCookies();
for (int i = 0; cookies != null && i < cookies.length; i++) {
if (cookies[i].getName().equals("bookHistory")) {
bookHistory = cookies[i].getValue();
}
}

// 第一种可能，那么返回的就是浏览的这个商品的id
if (bookHistory == null) {
return id;
}
// 第二种可能，要判断有没有包含，要先转成List，调用List的方法判断String.content判断出来的数据是有错误的，判断1的话21也包含
// 由于增删改查操作较多，所以用链表
LinkedList<String> list = new LinkedList(Arrays.asList(bookHistory
.split("\\,")));
/*
* if(list.contains(id)) { list.remove(id); list.addFirst(id); } else {
* //第三种和第四种可能 //第三种可能 if(list.size()>=3) { list.removeLast();
* list.addFirst(id); } else { //第四种可能 list.addFirst(id); } }
*/
// 上面的代码优化，不管怎么样都要list.addFirst(id);
if (list.contains(id)) {
list.remove(id);
} else {
if (list.size() >= 3) {
list.removeLast();
}
}
list.addFirst(id);

// 将list中的数据构建字符串返回
StringBuffer sb = new StringBuffer();
for (String bid : list) {
sb.append(bid + ",");
}
return sb.deleteCharAt(sb.length() - 1).toString();
}

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

}