C# 之 服务端获取远程资源

　　获取指定网页的远程资源可使用 WebClient、WebRequest、HttpWebRequest 三种方式来实现。当然也可使用webBrowse，webBrowse不做介绍。

　　通过 System.Net 名称空间下 WebClient 类下载文件。

//通过WebClient下载网页的源码
string url = "http://www.example.com";
System.Net.WebClient client = new System.Net.WebClient();
client.Encoding = System.Text.Encoding.UTF8;
string strHtml = client.DownloadString(url);

综合实例：

using System;
using System.Text;

using System.IO;
using System.Net;

namespace SnapUtility
{
public class ServerResourceHelper
{
/// <summary>
/// 通过WebClient获取远程资源
/// </summary>
/// <param name="url"></param>
/// <returns></returns>
public static string GetByWebClient(string url)
{
string strReturn = null;
WebClient client = new WebClient();
//client.Headers.Add(HttpRequestHeader.Accept, @"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
//client.Headers.Add(HttpRequestHeader.Referer, null);
//client.Headers.Add(HttpRequestHeader.UserAgent, @" Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36");
//client.Headers.Add(HttpRequestHeader.ContentType, "application/octet-stream");

string strExtension = Path.GetExtension(url); //扩展名
if (String.IsNullOrEmpty(strExtension))
{
Stream stream = client.OpenRead(url);
StreamReader streamReader = new StreamReader(stream, Encoding.GetEncoding("utf-8"));
strReturn = streamReader.ReadToEnd();
streamReader.Close();
stream.Close();
}
else
{
string path = "../WebSnap/DownLoad/";
path = System.Web.HttpContext.Current.Server.MapPath(path);

//自动创建文件夹
if (!Directory.Exists(path))
{
Directory.CreateDirectory(path);
}
path += DateTime.Now.ToString("hhmmss") + strExtension;

client.DownloadFile(new Uri(url), path);
}
client.Dispose();
return strReturn;
}

/// <summary>
/// 通过WebRequest获取远程资源
/// </summary>
/// <param name="url"></param>
/// <returns></returns>
public static string GetByWebRequest(string url)
{
string strReturn = null;
Uri uri = new Uri(url);
WebRequest request = WebRequest.Create(uri);
WebResponse response = request.GetResponse();
Stream stream = response.GetResponseStream();

string strExtension = Path.GetExtension(url); //扩展名
if (String.IsNullOrEmpty(strExtension))
{
StreamReader streamReader = new StreamReader(stream, Encoding.GetEncoding("utf-8"));
strReturn = streamReader.ReadToEnd();
streamReader.Close();
stream.Close();
response.Close();
}
else
{
string fileName = DateTime.Now.ToString("hhmmss") + strExtension;
long length = response.ContentLength;
strReturn = SaveFile(ref stream, fileName, length);
}
return strReturn;
}

/// <summary>
/// 通过WebRequest的Http特定实现获取远程资源
/// </summary>
/// <param name="url">远程地址</param>
/// <returns></returns>
public static string GetByHttpWebRequest(string url)
{
string strReturn = null;
Uri uri = new Uri(url);
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream stream = response.GetResponseStream();

string strExtension = Path.GetExtension(url); //扩展名
if (String.IsNullOrEmpty(strExtension))
{
StreamReader streamReader = new StreamReader(stream, System.Text.Encoding.GetEncoding("utf-8"));
strReturn = streamReader.ReadToEnd();
streamReader.Close();
stream.Close();
response.Close();
}
else
{
string fileName = DateTime.Now.ToString("hhmmss") + strExtension;
long length = response.ContentLength;
strReturn = SaveFile(ref stream, fileName, length);
}
return strReturn;
}

/// <summary>
/// FileStream保存文件
/// </summary>
/// <param name="stream"></param>
private static string SaveFile(ref Stream stream, string fileName, long length)
{
byte[] buffer = new byte[length];
stream.Read(buffer, 0, buffer.Length);
stream.Close();

string path = AppDomain.CurrentDomain.BaseDirectory + "DownLoad\\" + fileName;
FileStream fileStream = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write);
fileStream.Write(buffer, 0, buffer.Length);
fileStream.Flush();
fileStream.Close();

return path;
}

/// <summary>
/// 保存图片
/// </summary>
/// <param name="stream"></param>
private static string SavePicture(ref Stream stream, string fileName)
{
System.Drawing.Image image = System.Drawing.Image.FromStream(stream);
stream.Close();
string path = "../WebSnap/DownLoad/";
path = System.Web.HttpContext.Current.Server.MapPath(path);

//自动创建文件夹
if (!Directory.Exists(path))
{
Directory.CreateDirectory(path);
}
path += fileName;

image.Save(path, System.Drawing.Imaging.ImageFormat.Png);
image.Dispose(); //释放资源

return path;
}
}
}

注意：

“utf-8”应与指定网页的编码对应。

可以看到HttpWebRequest 方式最复杂，但确提供了更多的选择性。

有的网站检测客户端的UserAgent！如163