异步获取远程文件

using System;
using System.IO;
using System.Net;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace Test
{
    public class RequestState
    {
        const int BUFFER_SIZE = 1024;
        public StringBuilder requestData;
        public byte[] BufferRead;
        public HttpWebRequest request;
        public HttpWebResponse response;
        public Stream streamResponse;

        public RequestState()
        {
            BufferRead = new byte[BUFFER_SIZE];
            requestData = new StringBuilder("");
            request = null;
            streamResponse = null;
        }
    }

    public class HttpWebRequest_BeginGetResponse
    {
        public static ManualResetEvent allDone = new ManualResetEvent(false);
        const int BUFFER_SIZE = 1024;
        const int DefaultTimeout = 2 * 60 * 1000; // 2 minutes timeout

        // Abort the request if the timer fires.
        private static void TimeoutCallback(object state, bool timedOut)
        {
            if (timedOut)
            {
                HttpWebRequest request = state as HttpWebRequest;
                if (request != null)
                {
                    request.Abort();
                }
            }
        }

        public void Read()
        {
            try
            {
                // Create a HttpWebrequest object to the desired URL. 
                HttpWebRequest myHttpWebRequest = (HttpWebRequest)WebRequest.Create(@"http://passport.cnblogs.com/login.aspx");

                RequestState myRequestState = new RequestState();
                myRequestState.request = myHttpWebRequest;

                IAsyncResult result = (IAsyncResult)myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback), myRequestState);
                ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle, new WaitOrTimerCallback(TimeoutCallback), myHttpWebRequest, DefaultTimeout, true);
                allDone.WaitOne();
                myRequestState.response.Close();
            }
            catch (WebException e)
            {
                Console.WriteLine("\nMain Exception raised!");
                Console.WriteLine("\nMessage:{0}", e.Message);
                Console.WriteLine("\nStatus:{0}", e.Status);
                Console.WriteLine("Press any key to continue..........");
            }
            catch (Exception e)
            {
                Console.WriteLine("\nMain Exception raised!");
                Console.WriteLine("Source :{0} ", e.Source);
                Console.WriteLine("Message :{0} ", e.Message);
                Console.WriteLine("Press any key to continue..........");
                Console.Read();
            }
        }
        private static void RespCallback(IAsyncResult asynchronousResult)
        {
            try
            {
                // State of request is asynchronous.
                RequestState myRequestState = (RequestState)asynchronousResult.AsyncState;
                HttpWebRequest myHttpWebRequest = myRequestState.request;
                myRequestState.response = (HttpWebResponse)myHttpWebRequest.EndGetResponse(asynchronousResult);

                // Read the response into a Stream object.
                Stream responseStream = myRequestState.response.GetResponseStream();
                myRequestState.streamResponse = responseStream;

                // Begin the Reading of the contents of the HTML page and print it to the console.
                IAsyncResult asynchronousInputRead = responseStream.BeginRead(myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
                return;
            }
            catch (WebException e)
            {
                Console.WriteLine("\nRespCallback Exception raised!");
                Console.WriteLine("\nMessage:{0}", e.Message);
                Console.WriteLine("\nStatus:{0}", e.Status);
            }
            allDone.Set();
        }

        private static void ReadCallBack(IAsyncResult asyncResult)
        {
            try
            {
                RequestState myRequestState = (RequestState)asyncResult.AsyncState;
                Stream responseStream = myRequestState.streamResponse;
                int read = responseStream.EndRead(asyncResult);
                // Read the HTML page and then print it to the console.
                if (read > 0)
                {
                    myRequestState.requestData.Append(Encoding.ASCII.GetString(myRequestState.BufferRead, 0, read));
                    IAsyncResult asynchronousResult = responseStream.BeginRead(myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
                    return;
                }
                else
                {
                    Console.WriteLine("\nThe contents of the Html page are : ");
                    if (myRequestState.requestData.Length > 1)
                    {
                        string stringContent;
                        stringContent = myRequestState.requestData.ToString();
                        Console.WriteLine("\t");
                        Console.WriteLine("\t");
                        Console.WriteLine("\t");
                        Console.WriteLine("\t");
                        Console.WriteLine(stringContent);
                        Console.WriteLine("\t");
                        Console.WriteLine("\t");
                    }
                    Console.WriteLine("Press any key to continue..........");
                    Console.ReadLine();

                    responseStream.Close();
                }
            }
            catch (WebException e)
            {
                Console.WriteLine("\nReadCallBack Exception raised!");
                Console.WriteLine("\nMessage:{0}", e.Message);
                Console.WriteLine("\nStatus:{0}", e.Status);
            }
            allDone.Set();
        }
    }
}