我怎么才能赶上404？

小开

I think if you catch a WebException there is some information in there that you can use to determine if it was a 404. That's the only way I know of at the moment...I'd be interested in knowing any others...

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

小开

最佳答案

Use the HttpStatusCode Enumeration, specifically HttpStatusCode.NotFound

Something like:

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

Where
we is a WebException.

小开

Check out this snipit. The GetResponse will throw a WebRequestException. Catch that and you can get the status code from the response.

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);
}

this came from http://msdn.microsoft.com/en-us/library/system.net.webexception.status.aspx

小开

See at MSDN about status of the response:

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

小开

I haven't tested this, but it should work

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;
}

小开

Catch the proper exception type 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");
}

小开

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
}
}

小开

For VB.NET folks browsing this, I believe we can catch the exception only if it truly is a 404. Something like:

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

小开

In C# 6 you can use 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
}

小开

when POST or GET data to the server using WebRequest class then the type of exception would be WebException.Below is the code for file not found exception

//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);
}
}