【IT168 技术文档】

    最近一个项目中，需要让每个镜像站点同步更新。我在服务器A生成文件，再调到BCDE四台服务器的WebService进行下载更新。

    调动时把所以文件的地址作为一个字符串参数传递，最初的下载方法如下：

public static void DownloadFile(string uri, string filename)
{
WebClient wc = new WebClient();
wc.DownloadFile(uri, filename);
} 

    下载少量文件没有出现问题，当文件数达到几万级时，就出现文件没有更新过去。跟踪错误显示WebRequest请求超时，这时想到设定
    TimeOut的值来让它不超时，可是WebClient似乎没有这一属性，只得改用HttpWebRequest了，更改后如下：

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(SiteDomain);
request.Timeout = TIME_OUT;
private bool DownloadFile(string uri, string FileName, HttpWebRequest request)
{
request = (HttpWebRequest)WebRequest.Create(uri);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream resStream = response.GetResponseStream();
StreamReader streamReader = new StreamReader(resStream, System.Text.Encoding.Default);
string content = streamReader.ReadToEnd();
Business.IO.WriteFile(FileName, content);
return true;
} 

    把HttpWebRequest的Timeout在方法外面赋值，就不用每下载一个文件赋值一次。这样改后就搞定超时问题。下载大文件就采用异步处理，源码如下：

private bool DownloadBigFile(string uri, string FileName)
{
//创建文件 
if (!File.Exists(FileName))
{
FileStream s = File.Create(FileName);
s.Close();
}
else
{
FileStream s = new FileStream(FileName, FileMode.Create, FileAccess.Write);
s.Close();
}
//请求URL 
WebRequest request = WebRequest.Create(uri);
request.Timeout = TIME_OUT;
RequestState state = new RequestState(FileName);
state.Req = request;
//异步获取 
request.BeginGetResponse(new AsyncCallback(RespCallback), state);
//线程等侍 
reset.WaitOne();
return true;
}
//返回流回调方法 
private void RespCallback(IAsyncResult ar)
{
RequestState state = (RequestState)ar.AsyncState;
WebRequest request = state.Req;
//获取返回流 
WebResponse response = request.EndGetResponse(ar);
state.Res = response;
Stream stream = response.GetResponseStream();
IAsyncResult isar = stream.BeginRead(state.Buffer, 0, BUFFER_SIZE, new AsyncCallback(ReadCallack), state);
}
//读取字符串回调方法 
private void ReadCallack(IAsyncResult ar)
{
RequestState state = (RequestState)ar.AsyncState;
WebResponse response = state.Res;
Stream stream = response.GetResponseStream();
int i = stream.EndRead(ar);
if (i > 0)
{
state.WriteByte(i);
stream.BeginRead(state.Buffer, 0, BUFFER_SIZE, new AsyncCallback(ReadCallack), state);
}
else
{
//读取完成 
stream.Close();
//关闭文件输出流 
state.Close();
reset.Set();
}
return;
}
//异步状态私有类 
private class RequestState
{
private static Stream stream;
public byte[] Buffer;
public WebRequest Req;
public WebResponse Res;
public RequestState(string FileName)
{
Buffer = new byte[BUFFER_SIZE];
stream = new FileStream(FileName, FileMode.Append, FileAccess.Write);
}
public void WriteByte(int i)
{
stream.Write(Buffer, 0, i);
stream.Flush();
}
public void Close()
{
stream.Close();
}
}