Can't access subfolders on FTP server using Apache Commons FTPClient

Question

I want to download files which are in subfolder on FTP server but I see that my client can't access subfolders.

I wrote simple code to list all files in subfolder:

 public static void main(String[] args) throws IOException {
    FTPClient ftpClient = new FTPClient();

    ftpClient.connect(HOST, PORT);
    ftpClient.login(USER, PASS);
    ftpClient.enterLocalPassiveMode();
    ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

    FTPFile[] files = ftpClient.listFiles("/archive");
    int length = files.length;
    System.out.println("Number of files: " + length);

    ftpClient.logout();
    ftpClient.disconnect();
}

But length of files array is zero.

When I run this program on main directory files are listed properly.

Answer 1

Your code is ok. It should work on most servers. Your code will send this command to the server:

LIST /archive

That's correct (assuming the server uses this path syntax [slash] to refer to a subfolder of the root folder).

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But some (obscure) servers have problems with arguments passed to the LIST command.

Try this code instead:

ftpClient.cwd("archive");
FTPFile[] files = ftpClient.listFiles();

The above will send:

CWD archive
LIST

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Another approach worth trying is removing the leading slash, as the server may use a different path delimiter:

FTPFile[] files = ftpClient.listFiles("archive");