http://www.jb51.net/article/77726.htm

PHP第一次会话时会有Set-Cookie响应头返回,设置上PHPSESSID cookie

1. Cache-Control:
   no-store, no-cache, must-revalidate, post-check=0, pre-check=0
2. Connection:
   Keep-Alive
3. Content-Length:
   4865
4. Content-Type:
   text/html; charset=utf-8
5. Date:
   Mon, 09 Apr 2018 03:24:55 GMT
6. Expires:
   Thu, 19 Nov 1981 08:52:00 GMT
7. Keep-Alive:
   timeout=5, max=99
8. Pragma:
   no-cache
9. Server:
   ***********************************************
10. Set-Cookie:
    PHPSESSID=710f5dca0eb5ded010b840603c469f2d; path=/
11. X-Powered-By:
    **********

PHP之后的请求都会带上这个cookie作为标识，从而php能够从服务端的seesion管理中根据seesionid找到该回话的信息

1. Accept:
   image/webp,image/apng,image/*,*/*;q=0.8
2. Accept-Encoding:
   gzip, deflate
3. Accept-Language:
   zh-CN,zh;q=0.9
4. Connection:
   keep-alive
5. Cookie:
   PHPSESSID=710f5dca0eb5ded010b840603c469f2d
6. Host:
   production.whport.com.cn:30000
7. Referer:
   http://production.whport.com.cn:30000/SON_EXAM/user/login.php
8. User-Agent:
   Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36

关了浏览器，自然这个会话就没了。

如果设置了 session生存期，即使一直开着浏览器，超过生存期后访问，session实际已经被php释放了。自然就失效了(带过去之前的PHPSESSID也没用)。

JSP类似