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  • C#教程之C#采用HttpWebRequest实现保持会话上传文件

本文实例讲述了C#采用HttpWebRequest实现保持会话上传文件到HTTP的方法,在项目开发中有一定的实用价值,具体方法如下:

一、前言:

这篇文章翻译来自madmik3 写在 CodeProject 上的文章,原标题为: C#'s WebClient.UploadFile with more functionality.

二、正文:

我们使用 WebRequest 来获取网页内容是非常简单的,可是用他来上传文件就没有那么简单了。

如果我们在网页中上传文件,加入下面代码即可:

HTML 文件上传代码实例:

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<form action ="http://localhost/test.php" method = POST>
 <input type = text name = uname>
 <input type = password name =passwd>
 <input type = FILE name = uploadfile>
 <input type=submit>
</form>

但,如果在C#中使用 WebRequest 上传,必须对本地文件进行相应的处理才能提交到指定的HTTP地址,下面这个函数哦就帮我们做了这烦恼的操作

UploadFileEx 上传文件函数:

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public static string UploadFileEx( string uploadfile, string url, 
  string fileFormName, string contenttype,NameValueCollection querystring, 
  CookieContainer cookies) 
  if( (fileFormName== null) || 
    (fileFormName.Length ==0)) 
  
    fileFormName = "file"
  
 
  if( (contenttype== null) || 
    (contenttype.Length ==0)) 
  
    contenttype = "application/octet-stream"
  
   string postdata; 
  postdata = "?"
  if (querystring!=null
  
    foreach(string key in querystring.Keys) 
    
      postdata+= key +"=" + querystring.Get(key)+"&"
    
  
  Uri uri = new Uri(url+postdata); 
 
  string boundary = "----------" + DateTime.Now.Ticks.ToString("x"); 
  HttpWebRequest webrequest = (HttpWebRequest)WebRequest.Create(uri); 
  webrequest.CookieContainer = cookies; 
  webrequest.ContentType = "multipart/form-data; boundary=" + boundary; 
  webrequest.Method = "POST"
 
  // Build up the post message header 
  StringBuilder sb = new StringBuilder(); 
  sb.Append("--"); 
  sb.Append(boundary); 
  sb.Append(""); 
  sb.Append("Content-Disposition: form-data; name=\""); 
  sb.Append(fileFormName); 
  sb.Append("\"; filename=\""); 
  sb.Append(Path.GetFileName(uploadfile)); 
  sb.Append("\""); 
  sb.Append(""); 
  sb.Append("Content-Type: "); 
  sb.Append(contenttype); 
  sb.Append(""); 
  sb.Append("");       
 
  string postHeader = sb.ToString(); 
  byte[] postHeaderBytes = Encoding.UTF8.GetBytes(postHeader); 
 
  // Build the trailing boundary string as a byte array 
  // ensuring the boundary appears on a line by itself 
  byte[] boundaryBytes = 
      Encoding.ASCII.GetBytes("--" + boundary + ""); 
 
  FileStream fileStream = new FileStream(uploadfile, 
                FileMode.Open, FileAccess.Read); 
  long length = postHeaderBytes.Length + fileStream.Length + 
                      boundaryBytes.Length; 
  webrequest.ContentLength = length; 
 
  Stream requestStream = webrequest.GetRequestStream(); 
 
  // Write out our post header 
  requestStream.Write(postHeaderBytes, 0, postHeaderBytes.Length); 
 
  // Write out the file contents 
  byte[] buffer = new Byte[checked((uint)Math.Min(4096, 
               (int)fileStream.Length))]; 
  int bytesRead = 0; 
  while ( (bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0 ) 
    requestStream.Write(buffer, 0, bytesRead); 
 
  // Write out the trailing boundary 
  requestStream.Write(boundaryBytes, 0, boundaryBytes.Length); 
  WebResponse responce = webrequest.GetResponse(); 
  Stream s = responce.GetResponseStream(); 
  StreamReader sr = new StreamReader(s); 
 
  return sr.ReadToEnd(); 
}

调用代码如下:

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CookieContainer cookies = new CookieContainer(); 
//add or use cookies 
NameValueCollection querystring = new NameValueCollection(); 
querystring["uname"]="uname"
querystring["passwd"]="snake3"
string uploadfile;// set to file to upload 
uploadfile = "c:\\test.jpg"
 
//everything except upload file and url can be left blank if needed 
string outdata = UploadFileEx(uploadfile, 
   "http://localhost/test.php","uploadfile", "image/pjpeg"
   querystring,cookies);

至此,所有主要功能代码都已经介绍完毕,至于美化你的程序就要读者根据自己的喜好完成了。

作者还提供了接收文件的PHP代码,,个人觉得既然能写上传的程序,接收文件的Server Page应该不在话下的,况且又不是PHP才能接收提交的文件,ASP,ASP.NET,JSP都可以,这里就不再啰嗦了。


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