我怎样才能抓住404？

Question

我有以下代码：

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); 
request.Method = "HEAD"; 
request.Credentials = MyCredentialCache; 

try 
{ 
    request.GetResponse(); 
} 
catch 
{ 
} 

我如何能赶上一个特定的404错误？ WebExceptionStatus.ProtocolError只能检测到发生错误，但不能提供错误的确切代码。

例如：

catch (WebException ex) 
{ 
    if (ex.Status != WebExceptionStatus.ProtocolError) 
    { 
     throw ex; 
    } 
} 

是不足够有用的......协议的例外可能是401，503，403，什么真正的。

Answer 1

使用HttpStatusCode Enumeration，具体HttpStatusCode.NotFound

喜欢的东西：

HttpWebResponse errorResponse = we.Response as HttpWebResponse; 
if (errorResponse.StatusCode == HttpStatusCode.NotFound) { 
    // 
} 

w ^这里
we是WebException。

Answer 2

我想如果你发现了WebException那里有一些信息可以用来确定它是否是404这是我现在唯一知道的唯一方法我有兴趣知道任何其他...

catch(WebException e) { 
    if(e.Status == WebExceptionStatus.ProtocolError) { 
     var statusCode = (HttpWebResponse)e.Response).StatusCode); 
     var description = (HttpWebResponse)e.Response).StatusDescription); 
    } 
} 

Answer 3

看看这个snipit。 GetResponse会抛出WebRequestException。抓住这一点，你可以从响应中获得状态码。

try { 
    // Create a web request for an invalid site. Substitute the "invalid site" strong in the Create call with a invalid name. 
    HttpWebRequest myHttpWebRequest = (HttpWebRequest) WebRequest.Create("invalid site"); 

    // Get the associated response for the above request. 
    HttpWebResponse myHttpWebResponse = (HttpWebResponse) myHttpWebRequest.GetResponse(); 
    myHttpWebResponse.Close(); 
} 
catch(WebException e) { 
    Console.WriteLine("This program is expected to throw WebException on successful run."+ 
         "\n\nException Message :" + e.Message); 
    if(e.Status == WebExceptionStatus.ProtocolError) { 
     Console.WriteLine("Status Code : {0}", ((HttpWebResponse)e.Response).StatusCode); 
     Console.WriteLine("Status Description : {0}", ((HttpWebResponse)e.Response).StatusDescription); 
    } 
} 
catch(Exception e) { 
    Console.WriteLine(e.Message); 
} 

这个来自http://msdn.microsoft.com/en-us/library/system.net.webexception.status.aspx

Answer 4

StatusCode属性是什么，我想，你正在寻找。

Answer 5

看到MSDN关于响应的状态：

... 
catch(WebException e) { 
    Console.WriteLine("The following error occured : {0}",e.Status); 
} 
... 

Answer 6

我没有测试过这一点，但它应该工作

try 
{ 
    // TODO: Make request. 
} 
catch (WebException ex) 
{ 
    if (ex.Status == WebExceptionStatus.ProtocolError) { 
     HttpWebResponse resp = ex.Response as HttpWebResponse; 
     if (resp != null && resp.StatusCode == HttpStatusCode.NotFound) 
     { 
      // TODO: Handle 404 error. 
     } 
     else 
      throw; 
    } 
    else 
     throw; 
} 

Answer 7

赶上正确的异常类型WebException：

try 
{ 
    var request = (HttpWebRequest) WebRequest.Create(String.Format("http://www.gravatar.com/avatar/{0}?d=404", hashe)); 

    using(var response = (HttpWebResponse)request.GetResponse()) 
     Response.Write("has avatar"); 
} 
catch(WebException e) 
{ 
    if(e.Response.StatusCode == 404) 
    Response.Write("No avatar"); 
} 

Answer 8

try 
{ 
    var request = WebRequest.Create(uri); 
    using (var response = request.GetResponse()) 
    { 
     using (var responseStream = response.GetResponseStream()) 
     { 
      // Process the stream 
     } 
    } 
} 
catch (WebException ex) 
{ 
    if (ex.Status == WebExceptionStatus.ProtocolError && 
     ex.Response != null) 
    { 
     var resp = (HttpWebResponse) ex.Response; 
     if (resp.StatusCode == HttpStatusCode.NotFound) 
     { 
      // Do something 
     } 
     else 
     { 
      // Do something else 
     } 
    } 
    else 
    { 
     // Do something else 
    } 
} 

Answer 9

对于VB.NET乡亲浏览此，我相信我们可以捕获该异常，只有当它是一个真正的404是这样的：

Try 
    httpWebrequest.GetResponse() 
Catch we As WebException When we.Response IsNot Nothing _ 
           AndAlso TypeOf we.Response Is HttpWebResponse _ 
           AndAlso (DirectCast(we.Response, HttpWebResponse).StatusCode = HttpStatusCode.NotFound) 

    ' ... 

End Try 

Answer 10

在C＃6你可以使用exception filters。

try 
{ 
    var request = WebRequest.Create(uri); 
    using (var response = request.GetResponse()) 
    using (var responseStream = response.GetResponseStream()) 
    { 
     // Process the stream 
    } 
} 
catch(WebException ex) when ((ex.Response as HttpWebResponse)?.StatusCode == HttpStatusCode.NotFound) 
{ 
    // handle 404 exceptions 
} 
catch (WebException ex) 
{ 
    // handle other web exceptions 
} 

Answer 11

当POST或GET使用WebRequest类则异常的类型将是WebException.Below是代码数据服务器文件未发现异常

 //Create a web request with the specified URL 
      string path = @"http://localhost/test.xml1"; 
      WebRequest myWebRequest = WebRequest.Create(path); 

     //Senda a web request and wait for response. 
       try 
       { 
        WebResponse objwebResponse = myWebRequest.GetResponse(); 
        Stream stream= objwebResponse.GetResponseStream(); 

       } 
       catch (WebException ex) { 
        if (((HttpWebResponse)(ex.Response)).StatusCode == HttpStatusCode.NotFound) { 
         throw new FileNotFoundException(ex.Message); 
        } 

       }