请求头
    Accept: text/html,image/* —支持数据类型
    Accept-Charset: ISO-8859-1 —字符集
    Accept-Encoding: gzip —支持压缩
    Accept-Language:zh-cn —语言环境
    Host: www.itcast.cn:80 —访问主机
    If-Modified-Since: Tue, 11 Jul 2000 18:23:51 GMT —缓存文件的最后修改时间
    Referer: http://www.itcast.com/index.jsp —来自哪个页面、防盗链
    User-Agent: Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0)
    Cookie
    Connection: close/Keep-Alive —链接状态
    响应头
    Location: http://www.it315.org/index.jsp —跳转方向
    Server:apache tomcat —服务器型号
    Content-Encoding: gzip —数据压缩
    Content-Length: 80 —数据长度
    Content-Language: zh-cn —语言环境
    Content-Type: text/html; charset=GB2312 —数据类型
    Last-Modified: Tue, 11 Jul 2000 18:23:51 GMT —最后修改时间
    Refresh: 1;url=http://www.it315.org —定时刷新
    Content-Disposition: attachment; filename=aaa.zip —下载
    Set-Cookie:SS=Q0=5Lb_nQ; path=/search
    Expires: -1 —缓存
    Cache-Control: no-cache —缓存
    Pragma: no-cache —缓存
    Connection: close/Keep-Alive —连接