HttpStatusCode 读取问题

Question

我在从响应中获取 HttpStatusCode 时遇到了小问题。问题是当文件存在时我得到响应并且可以读取读取状态，但是当文件不存在时我看不到任何状态，即使我要求显示状态字符串。这是我的代码：

 Dim urls As New List(Of String)
        urls.Add("http://www.domain.com/test.php")
        urls.Add("http://www.domain.com/test2.php")
        urls.Add("http://www.domain.com/index.php")


        For Each Url As String In urls
            Dim response As HttpWebResponse = Nothing
            Try
                Dim request As HttpWebRequest = Net.HttpWebRequest.Create(Url)
                request.UserAgent = "Mozilla/5.0 (Windows; U; Windows NT 6.1; ru; rv:1.9.2.3) Gecko/20100401 Firefox/4.0 (.NET CLR 3.5.30729)"
                request.Method = "GET"
                response = request.GetResponse()

            Catch webex As WebException
            End Try

            If response.StatusCode = HttpStatusCode.OK = True Then
                MsgBox("File Url is correct: " & response.StatusCode.ToString)
            ElseIf response.StatusCode = HttpStatusCode.NotFound = True Then
                MsgBox("File Url is incorrect: " & Url)
            Else
                MsgBox(response.StatusCode.ToString)
            End If
        Next

Answer 1

当服务器没有返回成功状态码（2xx）时，框架总是抛出异常。但是，您仍然可以从异常对象中获得响应。

Function GetResponse(url As Uri) As WebResponse
    Dim response As WebResponse
    Dim request As HttpWebRequest = HttpWebRequest.Create(url)
    Try
        response = request.GetResponse()
    Catch serverErrors As WebException When serverErrors.Response IsNot Nothing
        response = serverErrors.Response
    Catch otherExceptions As Exception
        DoSomethingWith(otherExceptions)
    End Try
    Return response
End Function

Answer 2

问题在于，当文件不存在时，它会生成 WebException，而您的代码会默默地“吞下”这些异常。 IE。它抓住了它，什么也不做。

您需要在 catch 语句中添加一些检查错误的代码。

这可能是 How to properly catch a 404 error in .NET 的副本（尽管是 C# 而不是 VB）

Answer 3

如果我错了，请纠正我，但不应该这部分：

ElseIf response.StatusCode = HttpStatusCode.NotFound = True Then
           MsgBox("File Url is incorrect: " & Url)

其实是：

ElseIf response.StatusCode = HttpStatusCode.NotFound = True Then
           MsgBox("File Url is incorrect: " & Url & response.StatusCode.ToString)

如果您希望显示StatusCode。

关于您的评论：

但是当文件不存在时，我看不到任何状态

代码正在访问NotFound 枚举并进入代码块，但您并没有准确地显示代码中的状态。