C#采用HttpWebRequest實現保持會話上傳文件到HTTP的方法

2020-01-24 02:34:05

字體：大中小

來源：轉載

供稿：網友

本文實例講述了C#采用HttpWebRequest實現保持會話上傳文件到HTTP的方法，在項目開發中有一定的實用價值，具體方法如下：

一、前言：

這篇文章翻譯來自madmik3 寫在 CodeProject 上的文章，原標題為: C#'s WebClient.UploadFile with more functionality.

二、正文：

我們使用 WebRequest 來獲取網頁內容是非常簡單的，可是用他來上傳文件就沒有那么簡單了。

如果我們在網頁中上傳文件，加入下面代碼即可：

HTML 文件上傳代碼實例：

<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 上傳，必須對本地文件進行相應的處理才能提交到指定的HTTP地址，下面這個函數哦就幫我們做了這煩惱的操作

UploadFileEx 上傳文件函數：

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();  }

調用代碼如下：

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，所有主要功能代碼都已經介紹完畢，至于美化你的程序就要讀者根據自己的喜好完成了。

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