使用HttpWebRequest 一定要保证GetRequestStream和GetResponse对象关闭，否则容易造成连接处于CLOSE_WAIT状态
using (Stream stream = webReq.GetRequestStream())
{
stream.Write(buffer, , buffer.Length);
}
HttpWebResponse response = null;
try
{
response = webReq.GetResponse() as HttpWebResponse;
}
finally
{
try
{
if (response != null)
response.Close();
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