利用cookie实现查看最近浏览

package entity;
//书的实体类
public class Book {
private String id;
private String name;
private double price ;
public double getPrice() {
return price ;
}
public void setPrice(double price) {
this.price = price ;
}
private String author;
public Book(String id,String name, double price,String author ) {
// TODO Auto-generated constructor stub
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 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 + "]" ;
}

}

package utils;
import java.util.HashMap;
import java.util.Map;
//模拟数据库操作

import entity.Book;

public class DBUtils {
private static Map<String, Book> books= new HashMap<String,Book>();
//模拟数据库数据
static{
books.put("1" , new Book("1", "java入门",10,"小明" ));
books.put("2" , new Book("2", "oracle入门",10,"小红" ));
books.put("3" , new Book("3", "android入门",50,"小李" ));
books.put("4" , new Book("4", "大数据",90,"小刚" ));
}
//得到所有的书
public static Map<String, Book> getBooks(){
return books ;
}
//根据id查找书籍
public static Book  findBookById(String id ) {

return books .get(id );
}
}

package servlet;

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.sun.prism.impl.Disposer.Target;

import entity.Book;
import utils.DBUtils;

public class BookServlet extends HttpServlet {

/**
* Constructor of the object.
*/
public BookServlet() {
super();
}

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

response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.write("书籍推荐：<br/>");
Map<String, Book> books = DBUtils.getBooks();
//遍历books
for (Map.Entry<String, Book> book:books.entrySet()) {
out.write("<a href='"+request.getContextPath()+"/servlet/BookDetailsServlet"
+ "?id="+book.getKey()+"'"+"target='_blank'"+">"+book.getValue().getName()+"</a><
4000
br>");

}

out.write("<hr/>最近浏览的书有：<br>");
Cookie[] cookies = request.getCookies();
//遍历cookies
for (int i = 0;cookies!=null&& i < cookies.length; i++) {
if("historyBookId".equals(cookies[i].getName())){
String value = cookies[i].getValue();//1-2-3
String[] ids = value.split("-");
//遍历ids
for (int j = 0; j < ids.length; j++) {
Book book = DBUtils.findBookById(ids[j]);
out.print(" "+book.getName());
}
}
}
}

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

doGet(request, response);

}

}

import entity.Book;
import utils.DBUtils;

public class BookDetailsServlet extends HttpServlet {

/**
* Constructor of the object.
*/
public BookDetailsServlet() {
super();
}

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

response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
//显示图书的详细信息

//获得id
String id=request.getParameter("id");
Book book = DBUtils.findBookById(id);
//          out.write(book.toString());
out.print(book);
//把当前浏览过的书的id写回客户端
String historyBookId=organizeId(id,request);
Cookie cookie=new Cookie("historyBookId", historyBookId);
cookie.setPath("/");
cookie.setMaxAge(Integer.MAX_VALUE);
response.addCookie(cookie);
}

/**
*
客户端                  BookServlet          BookDetailsServlet
1.没有cookie的情况          1                    historyBook=1
2.有cookie，但没有historyBook                    historyBook=1
3.historyBook=1          2                    historyBook=2-1
4.historyBook=1-2          2                    historyBook=2-2
5.historyBook=1-2-3     3               historyBook=2-1-3
6.historyBook=1-2-3     4               historyBook=4-1-2
*/

private String organizeId(String id, HttpServletRequest request) {
// TODO Auto-generated method stub
//得到客户端Cookie
Cookie[] cookies = request.getCookies();
if(cookies==null){
return id;
}
Cookie historyBook=null;
//遍历cookies
for (int i = 0; i < cookies.length; i++) {
if("historyBookId".equals(cookies[i].getName())){
historyBook=cookies[i];
}
}
//如果没有historyBookId的cookie，则返回id
if(historyBook==null){
return id;
}
String value = historyBook.getValue();
//切割组织的id
String[] values = value.split("-");
LinkedList<String> list=new LinkedList<String>(Arrays.asList(values));
//如果小于3本书
if(list.size()<3){
//如何集合中包含该id，则删除原来的id，将id重新加到first
if(list.contains(id)){
list.remove(id);
}
}else {
if(list.contains(id)){
list.remove(id);
}else {//如果已经有3个id了，则将集合的最后一个id删除
list.removeLast();
}
}
list.addFirst(id);//将最新的书添加到最前面
StringBuffer sb=new StringBuffer();
//遍历list,在id之间加上'-'
for (int i = 0; i < list.size(); i++) {
if(i>0){
sb.append("-");
}
sb.append(list.get(i));
}
System.out.println(sb);
return sb.toString();
}

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

doGet(request, response);
}

}