2.Servlet与Cookie：
马克-to-win：Cookie有点像Session。Session是把键值对存在服务器端，一个Servlet存值 ，另外一个Servlet可以取值。Cookie也是以键值对的形式用于读取，不过是保存在客户端 浏览器的某个文本里面。取时，也要从这台机器的这个浏览器上去取。像Session一样，你 也可以设置过期时间，比如“一年”。和Session不同的是：用户可以把自己浏览器的Cookie工作系统关掉。这就是Cookie不如Session的重要的原因。不可靠，不保险。程序员编的程序都白费了。另外，对于Cookie来讲，servlet只能拿回属于自己整个Web应用的Cookie（别人的Web应用不行）。当然了，Session范围更小，只能拿回自己用户浏览器写过的东西。
马克-to-win：底下，我就给出一个Cookie的增删改查的例子。只需运行cookie.html。这个html带动四个增删改查Servlet。读者可以先增加Cookie,之后查询一下，再删除，再查询一下。反正自己研究研究这个例子。实验使用ie8做的，cookie的查找在例子当中。
注意此文件不能直接打开，只能拷贝到别的目录下，之后用记事本打开。我就这样打开后，给大家看一下。
mark-to-win0
yes0
localhost/ServletHello/
1024
2493888000
30731375
472266800
30657950
*
mark-to-win
yes
localhost/ServletHello/
1024
2172629504
30657951
472376800
30657950
*
执行了下面的delete之后，变成了:
mark-to-win0
yes0
localhost/ServletHello/
1024
414149632
30731383
2685375728
30657957
*
例：4.2.1:
cookie.html:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Cookie Test</title>
</head>
<body>
<FORM ACTION="AddCookie" METHOD="POST">
add<INPUT TYPE="SUBMIT" VALUE="Submit">
</FORM><br>
<FORM ACTION="DeleteCookie" METHOD="POST">
delete<INPUT TYPE="SUBMIT" VALUE="Submit">
</FORM><br>
<FORM ACTION="QueryCookie" METHOD="POST">
Query<INPUT TYPE="SUBMIT" VALUE="Submit">
</FORM><br>
<FORM ACTION="ModifyCookie" METHOD="POST">
Modify<INPUT TYPE="SUBMIT" VALUE="Submit">
</FORM><br>
</body>
</html>
package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class AddCookie extends HttpServlet {
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
Cookie returnVisitorCookie0 = new Cookie("mark-to-win0", "yes0");
Cookie returnVisitorCookie = new Cookie("mark-to-win", "yes");
Cookie returnVisitorCookie1 = new Cookie("mark-to-win1", "yes1");
/* public void setMaxAge(int expiry) Sets the maximum age of the cookie
* in seconds. A positive value indicates that the cookie will expire
* after that many seconds have passed. A negative value means that the
* cookie is not stored persistently and it won't be recorded in the
* file. will be deleted when the Web browser exits. A zero value causes
* the cookie to be deleted. By default, the value is -1, -1 indicating
* the cookie will persist until browser shutdown. in the cookie file,
* if the value is negative, it won't be recorded in the file. As long
* as the value is positive, itself and its expiry time will be recorded
* in the file. After that moment, that cookie expires, but that cookie
* is not deleted from the file, any way, there is schedule to expire in
* the file.另外，当你设置cookie时长为0，删除它后，如文件中所有cookie都被你用这种方法删除后，文件也会被ie自动删掉。你如果想删cookie文件，正常的得通过ie8设置中的删除钮。如果想看cookie文件，得拷贝文件到其他地方，之后用记事本看。*/
returnVisitorCookie0.setMaxAge(60 * 60 * 24 * 365); // 1 yea
returnVisitorCookie.setMaxAge(10 * 60 * 1);
response.addCookie(returnVisitorCookie0);
response.addCookie(returnVisitorCookie);
response.addCookie(returnVisitorCookie1);
response.sendRedirect("cookie.html");
}
}
更多请看：https://blog.csdn.net/qq_44594371/article/details/103166189
