1 String currentUrl=“http://www.cnblogs.com/notech”; //URL ?后面的内容为HTTP请求的正文URL url = new URL(currentUrl);
 2  
 3 HttpURLConnection httpurlconnection = url.openConnection();//下面的设置对应HTTP请求中的消息报头
 4 httpurlconnection.setRequestProperty("User-Agent",CommonValues.User_Agent);
 5 httpurlconnection.setRequestProperty("Accept",CommonValues.Accept);
 6 httpurlconnection.setRequestProperty("Accept-Charset",CommonValues.Accept_Charset);
 7 httpurlconnection.setRequestProperty("Accept-Language",CommonValues.Accept_Language);
 8 httpurlconnection.setRequestProperty("Connection",CommonValues.Connection);
 9 httpurlconnection.setRequestProperty("Keep-Alive",CommonValues.Keep_Alive);
10 httpurlconnection.setConnectTimeout(CommonValues.ConnectionTimeOut);
11 httpurlconnection.setReadTimeout(CommonValues.ReadTimeOut);
12              
13 httpurlconnection.connect();
14             
15 int responsecode = httpurlconnection.getResponseCode();
16              
17 if(responsecode == HttpURLConnection.HTTP_OK) //对应HTTP响应中状态行的响应码{
18 　　//操作请求流，这里对应HTTP响应中的响应正文
19 }
20              
21 if (httpurlconnection != null) 
22 {
23    httpurlconnection.disconnect();
24 }

We structure our discussion by (somewhat arbitrarily) dividing the protocol changes into nine major areas:

1.
Extensibility
2.
Caching
3.
Bandwidth optimization
4.
Network connection management
5.
Message transmission
6.
Internet address conservation
7.
Error notification
8.
Security, integrity, and authentication
9.
Content negotiation

Keepalive messages were not officially supported in HTTP 1.0. In HTTP 1.1 all connections are considered persistent, unless declared otherwise[1]. However, the default keepalive timeout of Apache 2.0 httpd is as little as 15 seconds]  and for Apache 2.2 only 5 seconds. The advantage of a short timeout is the ability to deliver multiple components of a web page quickly while not tying up multiple server processes or threads for too long.