转自MSDN
WebRequest是一个抽象类, HttpWebRequest和FtpWebRequest都是它的子类。
WebResponse也是一个抽象类, HttpWebResponse和FtpWebResponse都是它的子类。
WebRequest, HttpWebRequest能完成的工作WebClient也都能做,那他们有何区别?.Net框架中已经为我们提供了WebRequest和WebResponse两个强大的类来处理向URI标示的资源和获取数据了。然后,不足的是利用WebRequest和WebResponse时设置过于复杂。使用起来颇为费劲。于是乎有了现在的WebClient,WebClient其实可以理解为对WebRequest和WebResponse等协作的封装。它使人们使用起来更加简单方便,然后它也有先天不足的地方。那就是缺少对cookies/session的支持,用户无法对是否自动url转向的控制,还有就是缺少对代理服务器的支持。
使用异步操作将文件上载到 FTP 服务器
using System; using System.Net; using System.Threading; using System.IO; namespace Examples.System.Net { public class FtpState { private ManualResetEvent wait; private FtpWebRequest request; private string fileName; private Exception operationException = null; string status; public FtpState() { wait = new ManualResetEvent(false); } public ManualResetEvent OperationComplete { get {return wait;} } public FtpWebRequest Request { get {return request;} set {request = value;} } public string FileName { get {return fileName;} set {fileName = value;} } public Exception OperationException { get {return operationException;} set {operationException = value;} } public string StatusDescription { get {return status;} set {status = value;} } } public class AsynchronousFtpUpLoader { // Command line arguments are two strings: // 1. The url that is the name of the file being uploaded to the server. // 2. The name of the file on the local machine. // public static void Main(string[] args) { // Create a Uri instance with the specified URI string. // If the URI is not correctly formed, the Uri constructor // will throw an exception. ManualResetEvent waitObject; Uri target = new Uri (args[0]); string fileName = args[1]; FtpState state = new FtpState(); FtpWebRequest request = (FtpWebRequest)WebRequest.Create(target); request.Method = WebRequestMethods.Ftp.UploadFile; // This example uses anonymous logon. // The request is anonymous by default; the credential does not have to be specified. // The example specifies the credential only to // control how actions are logged on the server. request.Credentials = new NetworkCredential ("anonymous","[email protected]"); // Store the request in the object that we pass into the // asynchronous operations. state.Request = request; state.FileName = fileName; // Get the event to wait on. waitObject = state.OperationComplete; // Asynchronously get the stream for the file contents. request.BeginGetRequestStream( new AsyncCallback (EndGetStreamCallback), state ); // Block the current thread until all operations are complete. waitObject.WaitOne(); // The operations either completed or threw an exception. if (state.OperationException != null) { throw state.OperationException; } else { Console.WriteLine("The operation completed - {0}", state.StatusDescription); } } private static void EndGetStreamCallback(IAsyncResult ar) { FtpState state = (FtpState) ar.AsyncState; Stream requestStream = null; // End the asynchronous call to get the request stream. try { requestStream = state.Request.EndGetRequestStream(ar); // Copy the file contents to the request stream. const int bufferLength = 2048; byte[] buffer = new byte[bufferLength]; int count = 0; int readBytes = 0; FileStream stream = File.OpenRead(state.FileName); do { readBytes = stream.Read(buffer, 0, bufferLength); requestStream.Write(buffer, 0, readBytes); count += readBytes; } while (readBytes != 0); Console.WriteLine ("Writing {0} bytes to the stream.", count); // IMPORTANT: Close the request stream before sending the request. requestStream.Close(); // Asynchronously get the response to the upload request. state.Request.BeginGetResponse( new AsyncCallback (EndGetResponseCallback), state ); } // Return exceptions to the main application thread. catch (Exception e) { Console.WriteLine("Could not get the request stream."); state.OperationException = e; state.OperationComplete.Set(); return; } } // The EndGetResponseCallback method // completes a call to BeginGetResponse. private static void EndGetResponseCallback(IAsyncResult ar) { FtpState state = (FtpState) ar.AsyncState; FtpWebResponse response = null; try { response = (FtpWebResponse) state.Request.EndGetResponse(ar); response.Close(); state.StatusDescription = response.StatusDescription; // Signal the main application thread that // the operation is complete. state.OperationComplete.Set(); } // Return exceptions to the main application thread. catch (Exception e) { Console.WriteLine ("Error getting response."); state.OperationException = e; state.OperationComplete.Set(); } } } }如何使用 WebClient 类从 FTP 服务器下载文件
public static bool DisplayFileFromServer(Uri serverUri) { // The serverUri parameter should start with the ftp:// scheme. if (serverUri.Scheme != Uri.UriSchemeFtp) { return false; } // Get the object used to communicate with the server. WebClient request = new WebClient(); // This example assumes the FTP site uses anonymous logon. request.Credentials = new NetworkCredential ("anonymous","[email protected]"); try { byte [] newFileData = request.DownloadData (serverUri.ToString()); string fileString = System.Text.Encoding.UTF8.GetString(newFileData); Console.WriteLine(fileString); } catch (WebException e) { Console.WriteLine(e.ToString()); } return true; }
如何从 FTP 服务器上删除文件
public static bool DeleteFileOnServer(Uri serverUri) { // The serverUri parameter should use the ftp:// scheme. // It contains the name of the server file that is to be deleted. // Example: ftp://contoso.com/someFile.txt. // if (serverUri.Scheme != Uri.UriSchemeFtp) { return false; } // Get the object used to communicate with the server. FtpWebRequest request = (FtpWebRequest)WebRequest.Create(serverUri); request.Method = WebRequestMethods.Ftp.DeleteFile; FtpWebResponse response = (FtpWebResponse) request.GetResponse(); Console.WriteLine("Delete status: {0}",response.StatusDescription); response.Close(); return true; }