使用cookie法，查看最近看过的书

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import java.io.Serializable;

public class Book implements Serializable {
	private String id;
	private String name;
	private String price;
	private String auth;
	private String publish;
	private String description;
	
	public Book() {
	}
	
	public Book(String id,String name,String price,String auth,String publish,String description) {
		super();
		this.id = id;
		this.name = name;
		this.price = price;
		this.auth = auth;
		this.publish = publish;
		this.description = description;
	}

	public String getDescription() {
		return description;
	}

	public void setDescription(String description) {
		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 getPrice() {
		return price;
	}
	public void setPrice(String price) {
		this.price = price;
	}
	public String getAuth() {
		return auth;
	}
	public void setAuth(String auth) {
		this.auth = auth;
	}
	public String getPublish() {
		return publish;
	}
	public void setPublish(String publish) {
		this.publish = publish;
	}

}

import java.util.LinkedHashMap;
import java.util.Map;

import cn.huiyu.ben.Book;



public class BookDao {
	private static Map<String,Book> bookMap = new LinkedHashMap<String,Book>();
	private BookDao() {
	}
	static{
		bookMap.put("1",new Book("1","1111","11.0","zqwang","111出版社","222221111"));
		bookMap.put("2",new Book("2","2222","22.0","222出版社","222222222"));
		bookMap.put("3",new Book("3","3333","33.0","333出版社","333333333"));
	}
	
	public static Map<String,Book> getBooks(){
		return bookMap;
	}
	
	public static Book getBook(String id){
		return bookMap.get(id);
	}
}

public void doGet(HttpServletRequest request,HttpServletResponse response)
			throws ServletException,IOException {
		response.setContentType("text/html;charset=utf-8");
		//1.查询数据库中所有的书展示
		Map<String,Book> map = BookDao.getBooks();
		for(Map.Entry<String,Book> entry : map.entrySet()){
			Book book = entry.getValue();
			response.getWriter().write("<a href='"+request.getContextPath()+"/servlet/BookInfoServlet?id="+book.getId()+"'>"+book.getName()+"</a><br>");
		}
		response.getWriter().write("<hr>");
		
		//2.显示之前看过的书
		Cookie [] cs = request.getCookies();
		Cookie findC = null;
		if(cs!=null){
			for(Cookie c : cs){
				if("last".equals(c.getName())){
					findC = c;
				}
			}
		}
		if(findC == null){
			response.getWriter().write("没有看过任何书!");
		}else{
			response.getWriter().write("您曾经浏览过的书:<br>");
			String[] ids = findC.getValue().split(",");
			for(String id : ids){
				Book book = BookDao.getBook(id);
				response.getWriter().write(book.getName()+"<br>");
			}
		}
	}

public void doGet(HttpServletRequest request,IOException {
		response.setContentType("text/html;charset=utf-8");
		//1.获取要看的书的id,查询数据库找出书,输出书的详细信息
		String id = request.getParameter("id");
		Book book = BookDao.getBook(id);
		if(book==null){
			response.getWriter().write("找不到这本书!");
			return;
		}else{
			response.getWriter().write("<h1>书名:"+book.getName()+"</h1>");
			response.getWriter().write("<h3>作者:"+book.getAuth()+"</h3>");
			response.getWriter().write("<h3>售价:"+book.getPrice()+"</h3>");
			response.getWriter().write("<h3>出版社:"+book.getPublish()+"</h3>");
			response.getWriter().write("<h3>描述信息:"+book.getDescription()+"</h3>");
		}
		
		//2.发送cookie保存最后看过的书
		// --- 1 --> 1
		// 1 --2,1 --> 2,1
		// 2,1--3,2,1 --> 3,1
		// 3,1 -- 4,3,2 --> 4,2
		// 4,2 --3,4,2 --> 3,2
		String ids = "";
		
		Cookie [] cs = request.getCookies();
		Cookie findC = null;
		if(cs!=null){
			for(Cookie c : cs){
				if("last".equals(c.getName())){
					findC = c;
				}
			}
		}
		
		if(findC == null){
			//说明之前没有看过书的记录
			ids += book.getId();
		}else{
			//说明之前有历史看过的书的记录,需要根据历史记录算一个新的记录出来
			String [] olds = findC.getValue().split(","); 
			StringBuffer buffer = new StringBuffer();
			buffer.append(book.getId()+",");
			for(int i = 0;i<olds.length && buffer.toString().split(",").length<3 ;i++){
				String old = olds[i];
				if(!old.equals(book.getId())){
					buffer.append(old+",");
				}
			}
			ids = buffer.substring(0,buffer.length()-1);
		}
		
		
		
		Cookie lastC = new Cookie("last",ids);
		lastC.setMaxAge(3600*24*30);
		lastC.setPath(request.getContextPath());
		response.addCookie(lastC);
	}

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