WebRequest例子

闲暇之余，自己做了一个简单的优快云论坛最新问题浏览器，以便及时掌握“最新动态”，并增加了回贴机器人的功能。
程序界面如下:


主核心函数：

        Public Sub downloadFile()Sub downloadFile(ByVal Url As String, ByVal normalUserName As String, ByVal normalPassword As String, ByVal proxy As Boolean, ByVal proxyServer As String, ByVal proxyPort As Integer, ByVal proxyUserName As String, ByVal proxyPassword As String, ByVal Directory As String)
        Dim pfileWriter As StreamWriter = Nothing
        Dim sFile As String
        Dim length As Integer = 1024
        Dim Buffer(1025) As Char
        Dim bytesread As Integer = 0
        Dim ResolvedURI As Boolean = False

        While (Not ResolvedURI)
            Try
                If proxy Then
                    Dim proxyObject As System.Net.WebProxy = GetDefaultProxy()
                    proxyObject.BypassProxyOnLocal = True
                    GlobalProxySelection.Select = proxyObject
                End If

                'Create the request object
                Dim request As HttpWebRequest = CType(WebRequest.Create(Url), HttpWebRequest)
                request.AllowAutoRedirect = True
                If (normalUserName <> Nothing) Then
                    request.Credentials = New System.Net.CredentialCache
                End If
                If (proxyUserName <> Nothing) Then
                    request.Credentials = New System.Net.CredentialCache
                End If
                'Create the response object
                Dim response As HttpWebResponse = CType(request.GetResponse(), HttpWebResponse)

                Dim absolutePath, fileName As String
                absolutePath = response.ResponseUri.AbsolutePath
                'parse it from end to get the actual file name
                Dim i As Integer = InStrRev(absolutePath, "/")
                If (i > 0 And Len(absolutePath) > 1) Then
                    fileName = absolutePath.Substring(i)
                Else
                    fileName = "default.htm"
                End If
                'Console.WriteLine("file Name is {0}", fileName)
                'Console.WriteLine(response.StatusDescription)

                'Successfully resolved the URI
                ResolvedURI = True

                Dim myDirectory As String

                If (Directory.Length >= 3) Then
                    Dim j As Integer = Directory.LastIndexOf("")
                    If (j = Directory.Length) Then
                        myDirectory = Directory
                        sFile = Directory & fileName
                    Else
                        If myDirectory = "" Then myDirectory = Directory
                        If myDirectory.Substring(1) <> "" Then myDirectory = Directory & ""
                        sFile = myDirectory & fileName
                    End If
                End If

                Try
                    If (File.Exists(sFile)) Then
                        Select Case (MessageBox.Show("File Already Exist..Delete it..", "File Exists", MessageBoxButtons.OKCancel))
                            Case DialogResult.OK
                                File.Delete(sFile)
                            Case Else
                                Throw New ApplicationException("File exists change the file name before downloading")
                        End Select
                    End If

                    Try
                        Dim f As FileIOPermission = New FileIOPermission(FileIOPermissionAccess.AllAccess, myDirectory)
                        pfileWriter = New StreamWriter(New FileStream(sFile, FileMode.CreateNew, FileAccess.Write, FileShare.None))
                    Catch eArgNull As ArgumentNullException
                        ResolvedURI = True
                        MsgBox("null")
                    End Try
                Catch eIO As IOException
                    ResolvedURI = True
                    MsgBox("IO error")
                End Try

                Dim sr As StreamReader = New StreamReader(response.GetResponseStream(), System.Text.Encoding.Unicode)
                'Read from the stream and write any data to the console
                bytesread = sr.Read(Buffer, 0, length)
                pfileWriter.Write(Buffer, 0, bytesread)

                While (bytesread > 0)
                    'Console.Write( Buffer,0, bytesread);
                    pfileWriter.Write(Buffer, 0, bytesread)
                    bytesread = sr.Read(Buffer, 0, length)
                End While

            Catch WebExcp As WebException
                'If you get to Me point, the exception has been caught
                MsgBox("A WebException has been caught!" & Chr(13) & WebExcp.ToString())
                Dim st As Integer = Convert.ToInt32(WebExcp.Status)
                If (st = 7) Then ' 7 indicates a protocol error, thus a WebResonse object should exist
                    MsgBox("The protocol error returned by the server is " & Chr(10) & WebExcp.Message)
                End If
                'throw back to indicate user that error has occured
                ResolvedURI = True
            Catch UriExcp As UriFormatException
                ' If you get to Me point, the exception has been caught
                Console.WriteLine("A URIFormatException has been caught!" & Chr(10) & UriExcp.ToString())
                ResolvedURI = True
            Catch eOthers As Exception
                'throw back to indicate user that error has occured
                ResolvedURI = True
                MsgBox(eOthers.ToString)
            Finally
                If Not pfileWriter Is Nothing Then
                    pfileWriter.Close()
                End If
            End Try
            MsgBox("Resolved Complate")
        End While
    End Sub