我正在使用Visual C# 2005制作一个简单的程序，它可以在Yahoo! Finance上查找股票代码，下载历史数据，并为指定的股票代号绘制价格历史图表。
我知道需要获取数据的确切URL，如果用户输入一个现有的股票代号（或者至少是在Yahoo! Finance上有数据的），那么程序就能正常工作。但是，如果用户编造一个股票代号，程序会在运行时出现错误，因为程序尝试从不存在的网页中获取数据。
我正在使用WebClient类，并使用DownloadString函数。我浏览了WebClient类的所有其他成员函数，但没有看到任何我可以用来测试URL的东西。
我该怎么办？
这是另一种实现此解决方案的方法：
using System.Net;
///
/// Checks the file exists or not.
///
/// The URL of the remote file.
/// True : If the file exits, False if file not exists
private bool RemoteFileExists(string url)
{
try
{
//Creating the HttpWebRequest
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
//Setting the Request method HEAD, you can also use GET too.
request.Method = "HEAD";
//Getting the Web Response.
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
//Returns TRUE if the Status code == 200
response.Close();
return (response.StatusCode == HttpStatusCode.OK);
}
catch
{
//Any exception will returns false.
return false;
}
}
来源： http://www.dotnetthoughts.net/2009/10/14/how-to-check-remote-file-exists-using-c/
request.AllowAutoRedirect = false; 和 response.StatusCode == HttpStatusCode.Redirect (statusCode >= 100 && statusCode < 400) //Good requests) - Kiquenet你可以使用 "HEAD" 请求而不是 "GET" 请求来测试一个 URL，这样就可以避免下载内容带来的成本：
// using MyClient from linked post
using(var client = new MyClient()) {
client.HeadOnly = true;
// fine, no content downloaded
string s1 = client.DownloadString("http://google.com");
// throws 404
string s2 = client.DownloadString("http://google.com/silly");
}
在DownloadString周围使用try/catch来检查错误；没有错误？它就存在了...
使用C# 2.0（VS2005）：
private bool headOnly;
public bool HeadOnly {
get {return headOnly;}
set {headOnly = value;}
}
并且
using(WebClient client = new MyClient())
{
// code as before
}
/// <summary>
/// This method will check a url to see that it does not return server or protocol errors
/// </summary>
/// <param name="url">The path to check</param>
/// <returns></returns>
public bool UrlIsValid(string url)
{
try
{
HttpWebRequest request = HttpWebRequest.Create(url) as HttpWebRequest;
request.Timeout = 5000; //set the timeout to 5 seconds to keep the user from waiting too long for the page to load
request.Method = "HEAD"; //Get only the header information -- no need to download any content
using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
{
int statusCode = (int)response.StatusCode;
if (statusCode >= 100 && statusCode < 400) //Good requests
{
return true;
}
else if (statusCode >= 500 && statusCode <= 510) //Server Errors
{
//log.Warn(String.Format("The remote server has thrown an internal error. Url is not valid: {0}", url));
Debug.WriteLine(String.Format("The remote server has thrown an internal error. Url is not valid: {0}", url));
return false;
}
}
}
catch (WebException ex)
{
if (ex.Status == WebExceptionStatus.ProtocolError) //400 errors
{
return false;
}
else
{
log.Warn(String.Format("Unhandled status [{0}] returned for url: {1}", ex.Status, url), ex);
}
}
catch (Exception ex)
{
log.Error(String.Format("Could not test url {0}.", url), ex);
}
return false;
}
HttpWebRequest 如果在尝试下载其他内容之前不 .Close() response 对象，就会出现问题。找了好几个小时才发现这个问题！ - jbeldockHttpWebResponse对象实现了IDisposable接口，所以应该将其包含在using块中，这样可以确保连接被关闭。如果不这样做，可能会出现问题，就像@jbeldock遇到的那样。 - HabibHead 方法，但可能支持 Get 方法。它应该抛出405错误。 - Sriram Sakthivel如果我理解你的问题正确，你可以使用以下这种小方法来获取你URL测试的结果：
WebRequest webRequest = WebRequest.Create(url);
WebResponse webResponse;
try
{
webResponse = webRequest.GetResponse();
}
catch //If exception thrown then couldn't get response from address
{
return 0;
}
return 1;
private static async Task<bool> DoesUrlExists(String url)
{
try
{
using (HttpClient client = new HttpClient())
{
//Do only Head request to avoid download full file
var response = await client.SendAsync(new HttpRequestMessage(HttpMethod.Head, url));
if (response.IsSuccessStatusCode) {
//Url is available is we have a SuccessStatusCode
return true;
}
return false;
}
} catch {
return false;
}
}
我使用HttpClient.SendAsync和HttpMethod.Head一起，进行只发送Head请求而不下载整个文件。就像David和Marc所说，不仅有http 200表示OK，因此我使用IsSuccessStatusCode来允许所有成功的状态码。
我一直发现异常处理速度较慢。
也许有一种更简单的方法可以得到更好、更快的结果呢？
public bool IsValidUri(Uri uri)
{
using (HttpClient Client = new HttpClient())
{
HttpResponseMessage result = Client.GetAsync(uri).Result;
HttpStatusCode StatusCode = result.StatusCode;
switch (StatusCode)
{
case HttpStatusCode.Accepted:
return true;
case HttpStatusCode.OK:
return true;
default:
return false;
}
}
}
IsValidUri(new Uri("http://www.google.com/censorship_algorithm"));
result.IsSuccessStatusCode 而不是 switch？ - Dan Diplo试试这个（确保你使用System.Net）：
public bool checkWebsite(string URL) {
try {
WebClient wc = new WebClient();
string HTMLSource = wc.DownloadString(URL);
return true;
}
catch (Exception) {
return false;
}
}
//The checkWebsite command will return true:
bool websiteExists = this.checkWebsite("https://www.google.com");
//The checkWebsite command will return false:
bool websiteExists = this.checkWebsite("https://www.thisisnotarealwebsite.com/fakepage.html");
WebRequest request = WebRequest.Create("http://www.google.com");
try
{
request.GetResponse();
}
catch //If exception thrown then couldn't get response from address
{
MessageBox.Show("The URL is incorrect");`
}
public static bool isValidURL(string url) {
WebRequest webRequest = WebRequest.Create(url);
WebResponse webResponse;
try
{
webResponse = webRequest.GetResponse();
}
catch //If exception thrown then couldn't get response from address
{
return false ;
}
return true ;
}
public static bool UrlIsValid(string url)
{
bool br = false;
try {
IPHostEntry ipHost = Dns.Resolve(url);
br = true;
}
catch (SocketException se) {
br = false;
}
return br;
}