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

==============================================================================

ftp.txt 里的内容

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