使用cookie技术实现历史浏览记录并控制显示的个数

static{
	books.put(1, new Book(1,"java入门学习","tom"));
	books.put(2, new Book(2, "c#", "jack"));
	books.put(3, new Book(3, "python", "marray"));
	books.put(4, new Book(4,"大数据","kevin"));
	books.put(5, new Book(5, "javascipt入门", "lilie"));
	
}

public static Map<Integer, Book> getBookAll(){
	return DBUtils.books;
}

//根据id 获取书籍信息 key 就是数的id。
public static Book getBookById(Integer id){
	return books.get(id);
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 response.setContentType("text/html;charset=utf-8");
 //显示所有的书籍
 PrintWriter writer = response.getWriter();
 writer.println("图书列表:");
 
 Map<Integer, Book> bookMap = DBUtils.getBookAll();
 Set<Entry<Integer,Book>> entrySet = bookMap.entrySet();
 for (Entry<Integer, Book> entry : entrySet) {
	Book book = entry.getValue();
	 
	 writer.print("<br/><a href='http://localhost:8080"+request.getContextPath()+"/bookView?id="+book.getId()+"'>"+book.getName()+"</a>");
	 
}
 
 writer.println("<br/>访问的历史记录<br/>");
 //获取cookie
 Cookie[] cs = request.getCookies();
 if(cs !=null){
	 for (Cookie c : cs) {
		if("historyIDs".equals(c.getName())){
			String historyIDs = c.getValue();
			String[] split = historyIDs.split("-");
			for (String id : split) {
				Book book = DBUtils.getBookById(Integer.parseInt(id));
				writer.println("<br><a href='http://localhost:8080"+request.getContextPath()+"/bookView?id="+book.getId()+"'>"+book.getName()+"</a>");
			
			}
		}
	}
 }
 
 
}

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

	response.getWriter().println("详细信息:" + book.toString());

	LinkedList<String> list = new LinkedList<>();

	StringBuffer sb = new StringBuffer();

	// TODO 记录浏览信息，把id保存在cookie中，显示在页面
	// 把访问的id放入到cookie中
	Cookie[] cs = request.getCookies();
	if (cs != null) {
		// 说明原来已经有cookie其中保存了id
		// historyIDs = 1-2-3-4

		// 1-2-3-4-1 1-2-3-4-4 1-2-3-4 3
		for (Cookie c : cs) {
			if ("historyIDs".equals(c.getName())) {
				String idValues = c.getValue();
				System.out.println("以前访问的histroyIDs:" + idValues);

				// 页面只显示3个
				String[] ids = idValues.split("-");
				System.out.println("分割后的数组：" + Arrays.toString(ids));

				for (String id : ids) {
					list.add(id);
				}

				System.out.println("原来的集合元素:" + list);

				// 控制只添加三个id
				if (!list.contains(idStr)) {
					// 不包含重复元素

					if (list.size() == 3) {
						// 里面的元素等于3
						list.removeFirst();
					}
				} else {
					// 包含了重复的元素
					list.remove(idStr);

				}
				list.addFirst(idStr);

				System.out.println("添加新的id之后的集合元素:" + list);

				for (String id : list) {
					sb.append(id + "-");
				}

				idValues = sb.substring(0, sb.length() - 1);
				System.out.println("拼接后的histroyIDs:" + idValues);
				c.setValue(idValues);
				response.addCookie(c);

				/*
				 * //如果第一次访问和后来有范问同一个就直接结束方法 if
				 * (idValues.equals(idStr)){return;}
				 * 
				 * if(idValues.startsWith(idStr)){ idValues =
				 * idValues.replaceAll(idStr+"-", ""); }else{ idValues =
				 * idValues.replaceAll("-"+idStr, ""); }
				 * 
				 * 
				 * 
				 * 
				 * idValues += "-" + idStr;
				 * 
				 * System.out.println("现在histroyIDs:" + idValues); //
				 * 设置cookie的值 c.setValue(idValues); response.addCookie(c);
				 */

			}

		}
	} else {
		// 说明没有创建cookie
		Cookie cookie = new Cookie("historyIDs", idStr);
		cookie.setMaxAge(60 * 1);
		response.addCookie(cookie);
	}

}

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