In this post, I will guide you how to write Java code that downloads only structure (excluding files) of a remote directory on a FTP server, using Apache Commons Net API.

There would be a case in which we just want to download structure of a directory from a FTP server, excluding the files. That means creating a copy structure the remote directory on the local computer, not downloading remote files.

Based on the article How to download a complete folder from a FTP server, with some slightly modifications we have a cut-down version of the utility class as follows:

import java.io.File;
import java.io.IOException;

import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;

/**
 * This utility class provides a method that downloads a structure
 * of a directory (excluding files) from a FTP server, using
 * Apache Commons Net API.
 *
 * @author www.codejava.net
 *
 */
public class FTPDownloadUtil {

	/**
	 * Download structure of a directory from a FTP server.
	 * @param ftpClient an instance of org.apache.commons.net.ftp.FTPClient class.
	 * @param parentDir Path of the parent directory of the current directory being
	 * downloaded.
	 * @param currentDir Path of the current directory being downloaded.
	 * @param saveDir path of directory where the whole remote directory will be
	 * downloaded and saved.
	 * @throws IOException if any network or IO error occurred.
	 */
	public static void downloadDirStructure(FTPClient ftpClient, String parentDir,
			String currentDir, String saveDir) throws IOException {
		String dirToList = parentDir;
		if (!currentDir.equals("")) {
			dirToList += "/" + currentDir;
		}

		FTPFile[] subFiles = ftpClient.listFiles(dirToList);

		if (subFiles != null && subFiles.length > 0) {
			for (FTPFile aFile : subFiles) {
				String currentFileName = aFile.getName();
				if (currentFileName.equals(".") || currentFileName.equals("..")) {
					// skip parent directory and the directory itself
					continue;
				}

				if (aFile.isDirectory()) {
					String newDirPath = saveDir + parentDir + File.separator
						+ currentDir + File.separator + currentFileName;
					if (currentDir.equals("")) {
						newDirPath = saveDir + parentDir + File.separator
						+ currentFileName;
					}

					// create the directory in saveDir
					File newDir = new File(newDirPath);
					boolean created = newDir.mkdirs();
					if (created) {
						System.out.println("CREATED the directory: " + newDirPath);
					} else {
						System.out.println("COULD NOT create the directory: " + newDirPath);
					}

					// download the sub directory
					downloadDirStructure(ftpClient, dirToList, currentFileName,
							saveDir);
				}
			}
		}
	}
}

 

And here is code of a test program:

import java.io.IOException;

import org.apache.commons.net.ftp.FTPClient;

public class DownloadDirectoryStructureTest {

	public static void main(String[] args) {
		String server = "www.codejava.net";
		int port = 21;
		String user = "username";
		String pass = "password";

		FTPClient ftpClient = new FTPClient();

		try {
			// connect and login to the server
			ftpClient.connect(server, port);
			ftpClient.login(user, pass);

			// use local passive mode to pass firewall
			ftpClient.enterLocalPassiveMode();

			System.out.println("Connected");

			String remoteDirPath = "/Test";
			String saveDirPath = "E:\\Download";

			FTPDownloadUtil.downloadDirStructure(ftpClient, remoteDirPath, "",
					saveDirPath);

			// log out and disconnect from the server
			ftpClient.logout();
			ftpClient.disconnect();

			System.out.println("Disconnected");
		} catch (IOException ex) {
			ex.printStackTrace();
		}
	}
}

 

Compile the utility class and the test program:

javac -cp commons-net-VERSION.jar;. DownloadDirectoryStructureTest.java

Run the test program:

java -cp commons-net-VERSION.jar;. DownloadDirectoryStructureTest

Suppose the directory /Test on the FTP server has the following structure:

Then the test program produces the following output:

 

NOTES:Download the latest distribution of the Apache Commons Net library here.

 

Related Java FTP Tutorials:

• How to download a complete folder from a FTP server
• Upload only structure of a directory to FTP server
• Java FTP file download tutorial and example
• Use URLConnection to download file from FTP server

 

Other Java FTP Tutorials:

• Connect and login to a FTP server
• Java FTP create directory example
• Java FTP example - Change working directory
• Java FTP list files and directories example
• Java FTP file upload tutorial and example
• Java FTP delete file example
• Java FTP example - Search for files and directories