C#采用HttpWebRequest实现保持会话上传文件到HTTP的方法

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：

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：

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：

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。