VB.NET中使用FTP下载文件的两种方法

.net没有专门处理FTP的类，我们可以通过调用系统自带的FTP.EXE 或者是调用win32 API中的wininet.dll来完成基本操作。希望以下的代码能为大家抛砖引玉。

方法一： 使用Ftp.exe ，通过process类来调用它。

Imports System.Diagnostics

...

  Public Sub GetFileByCallFtp()

       '定义ProcessStartInfo，Process的启动信息。

        Dim psi As New ProcessStartInfo

        'ftp.exe的路径最好放到配置文件里。

        psi.FileName = "C:\WINNT\system32\ftp.exe"

        psi.RedirectStandardInput = False

        psi.RedirectStandardOutput = True

        '该值指示不使用操作系统Shell程序启动进程。

        psi.UseShellExecute = False

        '命令集文件名.注意,路径中不能有空格.

        Dim fileName As String = "C\ftp.txt"   

        '-s:FileName表示,从文件中读取控制命令

        psi.Arguments = "-s:" + fileName

        Dim proc As Process

        proc = Process.Start(psi)

        '等待进程完成任务

        proc.WaitForExit()

        '在控制台输出结果

        Console.WriteLine(proc.StandardOutput)

        Console.ReadLine()

    End Sub

方法二，使用win32 api —— wininet.dll

首先是，api声明：

   因为此测试程序，是VB.NET ConsoleApplication所以，api声明写在Module里，

   方法是静态的。所以没加Shared关键字， 这一点请大家注意。

    <DllImport("wininet")> _
    Public Function InternetOpen(ByVal sAgent As String, ByVal LAccessType As Integer, ByVal sProxyName As String, _
                                  ByVal SProxyBypass As String, ByVal lFlags As Integer) As Integer
    End Function

    <DllImport("wininet")> _
    Public Function InternetConnect(ByVal hInternetSession As Integer, ByVal sServerName As String, _
                                    ByVal nServerPort As Integer, ByVal sUsername As String, _
                                    ByVal sPassword As String, ByVal lService As Integer, _
                                    ByVal lFlags As Integer, ByVal lContext As Integer) As Integer
    End Function

    <DllImport("wininet")> _
    Public Function FtpGetFile(ByVal hFtpSession As Integer, ByVal lpszRemoteFile As String, _
                               ByVal lpszNewFile As String, ByVal fFailIfExists As Boolean, _
                               ByVal dwFlagsAndAttributes As Integer, ByVal dwFlags As Integer, _
                               ByVal dwContext As Integer) As Boolean
    End Function

    <DllImport("wininet")> _
    Public Function InternetCloseHandle(ByVal hInet As Integer) As Integer
    End Function

    调用：

     Public Sub GetFileByCallWininetDLL()
        Try
            Dim intinet As Integer = InternetOpen(Nothing, 0, Nothing, Nothing, 0)
            If intinet > 0 Then

                '参数：intinet的session值，ftp地址，端口，用户名，密码，lService， lFlags，lContext

                Dim intinetconn As Integer = InternetConnect(intinet, "192.168.110.152", 0, "tokiwa", "tokiwa", 1, 0, 0)

                If intinetconn > 0 Then

                    '下载某个文件到指定文件

                    Dim ret As Boolean = FtpGetFile(intinetconn, "pagerror.gif", "C:\itest.gif", 0, 0, 1, 0)

                    If ret Then
                        Console.WriteLine("ok!")
                        Console.ReadLine()
                    End If
                    InternetCloseHandle(intinetconn)
                    InternetCloseHandle(intinet)
                Else
                    Console.WriteLine("can't connect!")
                    Console.ReadLine()
                End If

            Else
                Console.WriteLine("ftp wrong!")
                Console.ReadLine()
            End If
        Catch ex As Exception
            Console.WriteLine(ex.Message)
            Console.ReadLine()
        End Try

    End Sub