VBNET从FTP下载文件，需要先判断文件是否存在吗

需要。

我们一直强调成都做网站、网站制作、成都外贸网站建设对于企业的重要性,如果您也觉得重要,那么就需要我们慎重对待,选择一个安全靠谱的网站建设公司,企业网站我们建议是要么不做，要么就做好,让网站能真正成为企业发展过程中的有力推手。专业网络公司不一定是大公司,成都创新互联作为专业的网络公司选择我们就是放心。

在实际使用FTP文件服务器的过程中，经常需要远程下载解析文件。为提高效率，需要判断文件存在与否，有选择的进行解析。

FTP协议是一个用于在计算机网络上客户端和服务器之间进行文件传输的应用层协议，包括FTP服务器和FTP客户端两个组成部分。FTP能操作任何类型的文件而不需要进一步处理，但有着极高的延时，从开始请求到第一次接收需求数据之间的时间较长，并不时地执行一些冗长的登录进程。

vb.net ftp上传文件

Dim OpenFileDialog As New OpenFileDialog

OpenFileDialog.InitialDirectory = My.Computer.FileSystem.SpecialDirectories.MyDocuments

OpenFileDialog.Filter = "文本文件(*.jpg)|*.jpg|所有文件(*.*)|*.*"

If (OpenFileDialog.ShowDialog(Me) = System.Windows.Forms.DialogResult.OK) Then

Dim FileName As String = OpenFileDialog.FileName

' TODO: 在此处添加打开文件的代码。

textbox1.Text = FileName

End If

第一个按钮 上传

Dim filelast As String = fileaddbefore.Text.Substring(fileaddbefore.Text.LastIndexOf("."), fileaddbefore.Text.Length - fileaddbefore.Text.LastIndexOf("."))

MessageBox.Show(filelast)

My.Computer.Network.UploadFile(textbox1.Text, "" 文件名.Text filelast, "登录名1", "登录密码", True, 100)

第二个按钮

vb.net FTP问题？

If My.Computer.Network.IsAvailable Then

'如果可用

Else

'不可用

End If

Public Sub DownloadFile ( _

address As Uri, _

destinationFileName As String, _

userName As String, _

password As String, _

showUI As Boolean, _

connectionTimeout As Integer, _

overwrite As Boolean, _

onUserCancel As UICancelOption _

)

参数

address

String 或 Uri。要下载的文件的路径，包括文件名和主机地址。必选。

destinationFileName

String。下载文件的文件名和路径。必选。

userName

String。要进行身份验证的用户名。默认值为空字符串 ""。

password

String。要进行身份验证的密码。默认值为空字符串 ""。

showUI

Boolean。指定是否显示操作进度。默认为 False。

connectionTimeout

Int32。以毫秒为单位的超时间隔。默认值为 100 秒。

overwrite

Boolean。指定是否改写现有文件。默认为 False。

onUserCancel

UICancelOption。指定当用户在对话框（此对话框在 ShowUI 设置为 True 时显示）上单击“取消”或“否”时的行为。默认为 ThrowException。

VB.net连接FTP操作

MSDN上的，看看对你有没有帮助。GOOD LUCK!

Imports System.Net

Imports System.IO

Module FtpSample

Sub Main(ByVal args() As String)

If args.Length = 0 OrElse args(0).Equals("/?") Then

DisplayUsage()

ElseIf args.Length = 1 Then

Download(args(0))

ElseIf args.Length = 2 Then

If args(0).Equals("/list") Then

List(args(1))

Else

Upload(args(0), args(1))

End If

Else

Console.WriteLine("Unrecognized argument.")

End If

End Sub

Private Sub DisplayUsage()

Console.WriteLine("USAGE:")

Console.WriteLine(" FtpSample [/? | FTP download URL | local file")

Console.WriteLine(" FTP upload URL | /list FTP list URL]")

Console.WriteLine()

Console.WriteLine("where")

Console.WriteLine(" FTP download URL URL of a file to download from an FTP server.")

Console.WriteLine(" FTP upload URL Location on a FTP server to upload a file to.")

Console.WriteLine(" FTP list URL Location on a FTP server to list the contents of.")

Console.WriteLine(" local file A local file to upload to an FTP server.")

Console.WriteLine()

Console.WriteLine(" Options:")

Console.WriteLine(" /? Display this help message.")

Console.WriteLine(" /list Specifies the list command.")

Console.WriteLine()

Console.WriteLine("EXAMPLES:")

Console.WriteLine(" Download a file FtpSample ")

Console.WriteLine(" Upload a file FtpSample upload.txt ")

End Sub

Private Sub Download(ByVal downloadUrl As String)

Dim responseStream As Stream = Nothing

Dim fileStream As FileStream = Nothing

Dim reader As StreamReader = Nothing

Try

Dim downloadRequest As FtpWebRequest = _

WebRequest.Create(downloadUrl)

Dim downloadResponse As FtpWebResponse = _

downloadRequest.GetResponse()

responseStream = downloadResponse.GetResponseStream()

Dim fileName As String = _

Path.GetFileName(downloadRequest.RequestUri.AbsolutePath)

If fileName.Length = 0 Then

reader = New StreamReader(responseStream)

Console.WriteLine(reader.ReadToEnd())

Else

fileStream = File.Create(fileName)

Dim buffer(1024) As Byte

Dim bytesRead As Integer

While True

bytesRead = responseStream.Read(buffer, 0, buffer.Length)

If bytesRead = 0 Then

Exit While

End If

fileStream.Write(buffer, 0, bytesRead)

End While

End If

Console.WriteLine("Download complete.")

Catch ex As UriFormatException

Console.WriteLine(ex.Message)

Catch ex As WebException

Console.WriteLine(ex.Message)

Catch ex As IOException

Console.WriteLine(ex.Message)

Finally

If reader IsNot Nothing Then

reader.Close()

ElseIf responseStream IsNot Nothing Then

responseStream.Close()

End If

If fileStream IsNot Nothing Then

fileStream.Close()

End If

End Try

End Sub

Private Sub Upload(ByVal fileName As String, ByVal uploadUrl As String)

Dim requestStream As Stream = Nothing

Dim fileStream As FileStream = Nothing

Dim uploadResponse As FtpWebResponse = Nothing

Try

Dim uploadRequest As FtpWebRequest = WebRequest.Create(uploadUrl)

uploadRequest.Method = WebRequestMethods.

' UploadFile is not supported through an Http proxy

' so we disable the proxy for this request.

uploadRequest.Proxy = Nothing

requestStream = uploadRequest.GetRequestStream()

fileStream = File.Open(fileName, FileMode.Open)

Dim buffer(1024) As Byte

Dim bytesRead As Integer

While True

bytesRead = fileStream.Read(buffer, 0, buffer.Length)

If bytesRead = 0 Then

Exit While

End If

requestStream.Write(buffer, 0, bytesRead)

End While

' The request stream must be closed before getting the response.

requestStream.Close()

uploadResponse = uploadRequest.GetResponse()

Console.WriteLine("Upload complete.")

Catch ex As UriFormatException

Console.WriteLine(ex.Message)

Catch ex As IOException

Console.WriteLine(ex.Message)

Catch ex As WebException

Console.WriteLine(ex.Message)

Finally

If uploadResponse IsNot Nothing Then

uploadResponse.Close()

End If

If fileStream IsNot Nothing Then

fileStream.Close()

End If

If requestStream IsNot Nothing Then

requestStream.Close()

End If

End Try

End Sub

Private Sub List(ByVal listUrl As String)

Dim reader As StreamReader = Nothing

Try

Dim listRequest As FtpWebRequest = WebRequest.Create(listUrl)

listRequest.Method = WebRequestMethods.

Dim listResponse As FtpWebResponse = listRequest.GetResponse()

reader = New StreamReader(listResponse.GetResponseStream())

Console.WriteLine(reader.ReadToEnd())

Console.WriteLine("List complete.")

Catch ex As UriFormatException

Console.WriteLine(ex.Message)

Catch ex As WebException

Console.WriteLine(ex.Message)

Finally

If reader IsNot Nothing Then

reader.Close()

End If

End Try

End Sub

End Module

可以通过设置 Credentials 属性来指定用于连接服务器的凭据，也可以将它们包含在传递给 Create 方法的 URI 的 UserInfo 部分中。

从 FTP 服务器下载文件时，如果命令成功，所请求的文件的内容即在响应对象的流中。通过调用 GetResponseStream 方法，可以访问此流。

如果使用 FtpWebRequest 对象向服务器上载文件，则必须将文件内容写入请求流，请求流是通过调用 GetRequestStream 方法或其异步对应方法（BeginGetRequestStream 和 EndGetRequestStream 方法）获取的。必须写入流并在发送请求之前关闭该流。

请求是通过调用 GetResponse 方法或其异步对应方法（BeginGetResponse 和 EndGetResponse 方法）发送到服务器的。请求的操作完成时，会返回一个 FtpWebResponse 对象。FtpWebResponse 对象提供操作的状态以及从服务器下载的所有数据。

网站题目：vbnetFTP的简单介绍
网站地址：http://ybzwz.com/article/hegded.html