如何在 C# 中捕获 FtpWebResponse 异常
我正在用 C# 构建一个 FTP 实用程序类。在调用 FtpWebRequest.GetResponse() 时引发 WebException 的情况下，在我的例子中，由于远程服务器上不存在所请求的文件而引发异常FtpWebResponse 变量超出范围。
但即使我在 try..catch 块之外声明变量，我也会收到一个编译错误，提示“使用未分配的局部变量'响应'”，但据我所知，没有办法分配它，直到您通过 FtpWebRequest.GetResponse() 方法分配响应。
有人可以建议吗，或者我错过了一些明显的事情吗？
谢谢！
这是我当前的方法：
private void Download(string ftpServer, string ftpPath, string ftpFileName, string localPath,
string localFileName, string ftpUserID, string ftpPassword)
{
FtpWebRequest reqFTP;
FtpWebResponse response;
try
{
reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://"
+ ftpServer + "/" + ftpPath + "/" + ftpFileName));
reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
reqFTP.UseBinary = true;
reqFTP.Credentials = new NetworkCredential(ftpUserID,
ftpPassword);
/* HERE IS WHERE THE EXCEPTION IS THROWN FOR FILE NOT AVAILABLE*/
response = (FtpWebResponse)reqFTP.GetResponse();
Stream ftpStream = response.GetResponseStream();
FileStream outputStream = new FileStream(localPath + "\\" +
localFileName, FileMode.Create);
long cl = response.ContentLength;
int bufferSize = 2048;
int readCount;
byte[] buffer = new byte[bufferSize];
readCount = ftpStream.Read(buffer, 0, bufferSize);
while (readCount > 0)
{
outputStream.Write(buffer, 0, readCount);
readCount = ftpStream.Read(buffer, 0, bufferSize);
}
ftpStream.Close();
outputStream.Close();
response.Close();
}
catch (WebException webex)
{
/*HERE THE response VARIABLE IS UNASSIGNED*/
if (response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable) {
//do something
}
}
I am building an FTP utility class in C#. In the case that a WebException is thrown on a call to FtpWebRequest.GetResponse(), in my case the exception is thrown for the requested file not existing on the remote server the FtpWebResponse variable is out of scope.
But even if I declare the variable outside the try..catch block I get a compile error saying "Use of unassigned local variable 'response'", but as far as I can tell there is no way to assign it until you assign the response via the FtpWebRequest.GetResponse() method.
Can someone please advise, or am I missing something obvious?
Thanks!
Here is my current method:
private void Download(string ftpServer, string ftpPath, string ftpFileName, string localPath,
string localFileName, string ftpUserID, string ftpPassword)
{
FtpWebRequest reqFTP;
FtpWebResponse response;
try
{
reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://"
+ ftpServer + "/" + ftpPath + "/" + ftpFileName));
reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
reqFTP.UseBinary = true;
reqFTP.Credentials = new NetworkCredential(ftpUserID,
ftpPassword);
/* HERE IS WHERE THE EXCEPTION IS THROWN FOR FILE NOT AVAILABLE*/
response = (FtpWebResponse)reqFTP.GetResponse();
Stream ftpStream = response.GetResponseStream();
FileStream outputStream = new FileStream(localPath + "\\" +
localFileName, FileMode.Create);
long cl = response.ContentLength;
int bufferSize = 2048;
int readCount;
byte[] buffer = new byte[bufferSize];
readCount = ftpStream.Read(buffer, 0, bufferSize);
while (readCount > 0)
{
outputStream.Write(buffer, 0, readCount);
readCount = ftpStream.Read(buffer, 0, bufferSize);
}
ftpStream.Close();
outputStream.Close();
response.Close();
}
catch (WebException webex)
{
/*HERE THE response VARIABLE IS UNASSIGNED*/
if (response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable) {
//do something
}
}
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评论（3）
作为解决此问题的通用方法，只需首先将
null分配给响应，然后检查 catch 块是否为null。但是，在这种特定情况下，您拥有
WebException实例所需的所有属性（包括 服务器响应）！As generic way to solve this, just assign
nullto the response first and then check in the catch block if it isnull.However, in this specific case, you have all the properties you need on the
WebExceptioninstance (including the server response)!问题的正确解决方案可以在这个问题中找到：
如何在 FtpWebRequest 之前检查 FTP 上是否存在文件
简而言之：
由于错误，您的“响应”变量将始终为空。您需要从“webex.Response”测试 FtpWebResponse（强制转换）以获取 StatusCode。
The correct solution to the problem can be found in this question here:
How to check if file exists on FTP before FtpWebRequest
In short:
Your 'response' variable will always be null because of the error. You need to test the FtpWebResponse from 'webex.Response' (cast it) to get the StatusCode.
好吧，你总是可以分配一个变量：
Well you could always assign a variable: