Cookie学习笔记《一》

一、什么是Cookie

     Cookie是一小段的文本信息,客户端请求服务器,如果服务器需要记录该用户状态,就使用response向客户端浏览器颁发一个Cookie.
客户端浏览器会把Cookie保存起来.当浏览器再请求该网站时,浏览器把请求的网址连同该Cookie一同提交给服务器.
     服务器检查该Cookie,以此来辨认用户状态.服务器还可以根据需要修改Cookie的内容.

     查看某个网站颁发的Cookie很简单：
     javascript:alert(document.cookie)

二、练习

Cookie.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" errorPage="login.jsp" %>
<%@ page import="javax.servlet.http.*"%> 

<%
	
	request.setCharacterEncoding("UTF-8"); //设置request编码
	String username = "";	//用户名
	int visitTimes = 0;		//访问次数
	
	Cookie[] cookies = request.getCookies();	//所有的Cookie
	for(int i=0; cookies!=null&&i<cookies.length;i++){		//遍历Cookie寻找账号与登录次数
		Cookie cookie = cookies[i];		//第i个Cookie
		if("username".equals(cookie.getName())){	//如果Cookie名为Username
			System.out.println(cookie.getValue());
			username = cookie.getValue();	//则记录该Cookie的内容
		}else if("visitTimes".equals(cookie.getName())){	//如果Cookie名为visitTimes
			visitTimes = Integer.parseInt(cookie.getValue());	//则记录Cookie的内容
		}
	}
	if(username == null || username.trim().equals("")){		//如果没有找到用户名，则转到登录界面 
		throw new Exception("您还没有登录,请先登录.");
	}
	//修改Cookie,更新用户的访问次数
	Cookie visitTimesCookie = new Cookie("visitTimes",Integer.toString(++visitTimes));
	response.addCookie(visitTimesCookie);
%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>cookie.jsp</title>
</head>
<body>
	<div align="center" style="margin:10px;">
		<fieldset>
			<legend>登录信息</legend>
			<form action="login.jsp" method="post">
				<table>
					<tr>
						<td>您的账号：</td>
						<td><%= username%></td>
					</tr>
					<tr>
						<td>登陆次数：</td>
						<td><%= visitTimes%></td>
					</tr>
					<tr>
						<td></td>					
						<td>
						<input type="button" value="刷新" onclick="location='<%= request.getRequestURI() %>?ts=' + new Date().getTime();" class="button">
						</td>
					</tr>
				</table>
			</form>
		</fieldset>
	</div>
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" isErrorPage="true" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<%
	request.setCharacterEncoding("UTF-8");
	response.setCharacterEncoding("UTF-8");
	
	if("POST".equals(request.getMethod())){
		
		Cookie usernameCookie = new Cookie("username",request.getParameter("username"));
		//Cookie visittimesCookie = new Cookie("visitTimes","0");
		
		response.addCookie(usernameCookie);
		//response.addCookie(visittimesCookie);
		
		//System.out.println(visittimesCookie.getValue());
		
		response.sendRedirect(request.getContextPath() + "/cookie.jsp");
		return;
	}
%>


<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>login.jsp</title>
</head>
<body>
	<div align="center" style="margin:10px;">
		<fieldset>
			<legend>登录</legend>
			<form action="login.jsp" method="POST">
				<table>
					<tr>
						<td></td>
						<td>
							<span style="color:red; ">
								<%= exception.getMessage() %>
							</span>
						</td>					
					</tr>
					<tr>
						<td>账号：</td>
						<td>
							<input type="text" name="username" style="width:200px; ">
						</td>
					</tr>
					<tr>
						<td>密码：</td>
						<td>
							<input type="password" name="password" style="width:200px; ">
						</td>
					</tr>
					<tr>
						<td></td>
						<td>
							<input type="submit" value="登录" class="button">
						</td>
					</tr>
				</table>
			</form>
		</fieldset>
	</div>
</body>
</html>

三、Cookie的不可跨域名性

       Cookie具有不可跨域名性.根据Cookie规范,浏览器访问某个网站只会携带该网站的Cookie,而不会携带别的网站的Cookie.
       需要注意的是：虽然网站images.google.com和www.google.com同属于Google，但是域名不一样，二者同样不能互相操作彼此的Cookie.

四、Unicode编码：保存中文

        中文与英文字符不同，中文属于Unicode字符,在内存中占4个字符,而英文属于ASCII字符,内存中占2个字节.
        Cookie中使用Unicode字符时需要对Unicode字符进行编码,否则会乱码.
        编码可以使用java.net.URLEncoder类的 encode(String str,String encoding)方法.
        解码使用java.net.URLDecoder类的decode(String str,String encoding)方法.

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@page import="java.net.URLDecoder"%>
<%@page import="java.net.URLEncoder"%>

<%
	//使用中文的Cookie. name与value都使用UTF-8编码
	Cookie cookie = new Cookie(URLEncoder.encode("姓名","UTF-8"),
							   URLEncoder.encode("刘京华","UTF-8"));
	response.addCookie(cookie);	//发送到客户端	
%>


<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Cookie Encoding</title>
</head>
<body>
<%
	Cookie[] cookie1 = request.getCookies();
	if(cookie1 != null){
		for(Cookie cc : cookie1){
			String cookieName = URLDecoder.decode(cc.getName(),"UTF-8");
			String cookieValue = URLDecoder.decode(cc.getValue(),"UTF-8");			
			out.println(cookieName + "=" + cookieValue + "; <br/>");
		}
	}else{
		out.println("Cookie 已经写入客户端.请刷新页面.");
	}
%>
</body>
</html>

Cookie学习笔记《一》

猜你喜欢