Cookie&Session

首页（显示用户上次访问的时间）

response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter  out = response.getWriter();
out.write("您上次访问时间是：");
//1.获取用户上次访问的时间，显示
Cookie cookies[] = request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++){
	Cookie cookie = cookies[i];
	if(cookie.getName().equals("lastAccessTime")){
		long time = Long.parseLong(cookie.getValue());
		Date date = new Date(time);
		out.write(DateFormat.getDateInstance(DateFormat.FULL).format(date));
	}
}
	
//2.把本次的时间以cookie的形式回写给客户机   (lastAccessTime)
Cookie cookie = new Cookie("lastAccessTime",System.currentTimeMillis()+"");
response.addCookie(cookie);

• 一个Cookie只能标识一种信息，它至少含有一个标识该信息的名称（NAME）和设置值（VALUE）。 
• 一个WEB站点可以给一个WEB浏览器发送多个Cookie，一个WEB浏览器也可以存储多个WEB站点提供的Cookie。
• 浏览器一般只允许存放300个Cookie，每个站点最多存放20个Cookie，每个Cookie的大小限制为4KB。
• 如果创建了一个cookie，并将他发送到浏览器，默认情况下它是一个会话级别的cookie（即存储在浏览器的内存中），用户退出浏览器之后即被删除。若希望浏览器将该cookie存储在磁盘上，则需要使用maxAge，并给出一个以秒为单位的时间。将最大时效设为0则是命令浏览器删除该cookie。
• 注意，删除cookie时，path必须一致，否则不会删除

显示用户上次浏览过的商品

public class CookieDemo1 extends HttpServlet {

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

		response.setContentType("text/html;charset=UTF-8");
		response.setCharacterEncoding("UTF-8");
		PrintWriter  out = response.getWriter();
		
		//1.显示网站所有商品
		out.print("本网站有如下书籍：<br/>");
		Map<String,Book> map = DB.getMap();
		for(Map.Entry<String, Book> entry : map.entrySet()){
			Book book = entry.getValue();
			out.print("<a href='/com/servlet/CookieDemo2?id="+book.getId()+"' target='_blank'>"+book.getName()+"</a><br/>");
		}
		
		
		
		out.print("您曾经看过如下商品：<br/>");
		//2.显示用户曾经浏览过的商品    //   bookHistory
		Cookie cookie = null;
		Cookie cookies[] = request.getCookies();
		for(int i=0;cookies!=null && i<cookies.length;i++){
			if(cookies[i].getName().equals("bookHistory")){
				cookie = cookies[i];
			}
		}
		if(cookie!=null){
			//找到了bookHistory这个cookie
			String bookHistory = cookie.getValue();   //4_6_1
			String ids[] = bookHistory.split("\\_");
			for(String id: ids){
				Book book = (Book) DB.getMap().get(id);
				out.print(book.getName() + "<br/>");
			}
		}
		
	}

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

}


class DB{
	private static Map<String,Book> map = new HashMap<String, Book>();
	static{
		map.put("1", new Book("1","图书1","张三"));
		map.put("2", new Book("2","图书2","李四"));
		map.put("3", new Book("3","图书3","王五"));
		map.put("4", new Book("4","图书4","赵六"));
		map.put("5", new Book("5","图书5","韩七"));
	}
	
	public static Map<String, Book> getMap(){
		return map;
	}
	
}

class Book{
	private String id;
	private String name;
	private String author;
	
	public Book() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Book(String id, String name, String author) {
		super();
		this.id = id;
		this.name = name;
		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;
	}
}

public class CookieDemo3 extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html;charset=UTF-8");
		response.setCharacterEncoding("UTF-8");
		PrintWriter  out = response.getWriter();
		
		//1.根据用户带过来的id值，显示相应商品的信息
		out.print("您想看的书的详细信息为：<br/>");
		String id = request.getParameter("id");
		Book book = (Book) DB.getMap().get(id);
		out.print(book.getId() + "<br/>");
		out.print(book.getName() + "<br/>");
		out.print(book.getAuthor() + "<br/>");
		
		
		//2.以cookie的形式回写该商品的id号给浏览器
		String bookHistory = makeCookie(book.getId(),request);
		Cookie cookie = new Cookie("bookHistory",bookHistory);
		cookie.setMaxAge(10000);
		response.addCookie(cookie);
		
	}

	//根据用户原来看过的书，以及现在看的书的id，构建新的cookie值
	private String makeCookie(String id, HttpServletRequest request) {
		
		//bookHistory=null    3     bookHistory=3
		//bookHistory=2_1_5   3     bookHistory=3_2_1
		//bookHistory=2       3     bookHistory=3_2
		//bookHistory=2_3     3     bookHistory=3_2
		
		
		//1.得到用户曾经看过的书
		String bookHistory = null;
		Cookie cookies[] = request.getCookies();
		for(int i=0;cookies!=null && i<cookies.length;i++){
			if(cookies[i].getName().equals("bookHistory")){
				bookHistory = cookies[i].getValue();
			}
		}
		
		if(bookHistory==null){
			bookHistory = id;
			return bookHistory;
		}

		//bookHistory=1_2_5    代表用户曾经看一些书，接着程序要得到用户曾经看过什么书
		String ids[] = bookHistory.split("_");
		//为了检测数组中是否包含当前id，我们应该把数据转成集合，并且还要转成链表结构的集合
		LinkedList<String> idList = new LinkedList(Arrays.asList(ids));
		/*if(idList.contains(id)){
			//bookHistory=2_3     3     bookHistory=3_2
			idList.remove(id);
			idList.addFirst(id);
		}else{
			//bookHistory=2_1_5   3     bookHistory=3_2_1
			if(idList.size()>=3){
				idList.removeLast();
				idList.addFirst(id);
			}else{
				//bookHistory=2       3     bookHistory=3_2
				idList.addFirst(id);
			}
		}*/
		if(idList.contains(id)){
			idList.remove(id);
		}else{
			if(idList.size()>=3){
				idList.removeLast();
			}
		}
		idList.addFirst(id);
		
		StringBuffer sb = new StringBuffer();
		for(String lid: idList){   //1_2_3_
			sb.append(lid + "_");
		}
		
		return sb.deleteCharAt(sb.length()-1).toString();
	}

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

} 

数据指纹(MD5:32|64)

public static String md5(String plainText) {
		
		try {
			MessageDigest md = MessageDigest.getInstance("MD5");
			md.update(plainText.getBytes());
			byte b[] = md.digest();
			int i;
			StringBuffer buf = new StringBuffer("");
			for (int offset = 0; offset < b.length; offset++) {
				i = b[offset];
				if (i < 0)
					i += 256;
				if (i < 16)
					buf.append("0");
				buf.append(Integer.toHexString(i));
			}
			System.out.println("result: " + buf.toString());// 32位的加密
			return buf.toString();
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException(e);
		}
	}

class TokenProcessor{
	//1.  把构造方法私有
	//2.  自己产生一个类的对象
	//3.  定义一个方法返回上面产生的对象
	
	private TokenProcessor(){};
	public static final TokenProcessor instance = new TokenProcessor();
	public static TokenProcessor getInstance(){
		return instance;
	}
	
	public String generateToken(){
		
		//3843849384   9849238402840243802  983434
		String token = System.currentTimeMillis() + "" + new Random().nextInt(99999999);
		
		//数据指纹 数据摘要  md5
		try {
			MessageDigest md = MessageDigest.getInstance("md5"); 
			byte md5[] = md.digest(token.getBytes());   //128位  16【12，23，34，544543543543，】
			
			//base64编码    SABDSSDSD
			BASE64Encoder encoder = new BASE64Encoder();
			return encoder.encode(md5);
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException(e);
		}
	}
}

 防止表单重复提交

<form action="/com/servlet/FormSubmitServlet" method="post" onsubmit="return dosubmit()">
    	用户名：<input type="text" name="username"><br/>
    	<input id="submit" type="submit" value="提交">
</form>

function dosubmit(){
			document.getElementById("submit").disabled = 'disabled';
			return true;
		}

response.setContentType("text/html;charset=UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter  out = response.getWriter();
String token = TokenProcessor.getInstance().generateToken();
request.getSession().setAttribute("token", token);		
out.print("<form action='/com/servlet/FormSubmitServlet' method='post'>");
out.print("<input type='hidden' name='token' value='"+token+"'>");
out.print("<input type='text' name='username'>");
out.print("<input type='submit' value='提交'>");
out.print("</form>");

public void doGet(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {
	boolean b = isToken(request);
	if(!b){
		//用户带过来的令牌无效，阻止提交
		System.out.println("你是重复提交！！");
		return;
	}
	
	//用户带过来的令牌有效，处理提交
	request.getSession().removeAttribute("token");
	
	String username = request.getParameter("username");
	//把用户提交的数据保存到数据库中
	System.out.println("处理提交请求，把" + username + "保存到数库中！！");
	
}
	//判断用户带过来的令牌是否有效
private synchronized boolean isToken(HttpServletRequest request) {
	String client_token = request.getParameter("token");
	if(client_token==null){
		return false;
	}
	
	String server_token = (String) request.getSession().getAttribute("token");
	if(server_token==null){
		return false;
	}
	
	if(!client_token.equals(server_token)){
		return false;
	}
	
	return true;
}

 

评论

1 楼 zone8089653 2013-05-12  

请教lz 在https下request.getCookies()值为null，应该怎么处理