我怎么能抓到404？

Question

我有以下代码:

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

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

如何捕获特定的404错误？WebExceptionStatus.ProtocolError只能检测到发生了错误,但未提供错误的确切代码.

例如:

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

只是没用得多......协议异常可能是401,503,403,真的是什么.

Answer 1

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 2

使用HttpStatusCode Enumeration,特别是HttpStatusCode.NotFound

就像是:

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

哪里
we是WebException.

Answer 3

在C#6中,您可以使用异常过滤器.

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 4

我没有测试过这个,但它应该可以工作

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;
}