Download Files Using Commons Net

Here is a simple program to download files from an FTP server using Commons Net,

package com.mm.ftpclient;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
import org.apache.commons.net.ftp.FTPFileFilter;
import org.apache.commons.net.ftp.FTPFileFilters;

public class FtpClientHelper {

    private String        host;
    private int            port        = 21;
    private FTPClient    ftpClient    = null;

    public FtpClientHelper(String ftpHost) throws Exception {
        this.host = ftpHost;
    }

    public List<String> listFiles(String ftpPath, FTPFileFilter ff, boolean recurse) throws IOException {
        List<String> files = new ArrayList<>();
        ff = ff == null ? FTPFileFilters.ALL : ff;
        FTPFile[] listFiles = ftpClient.listFiles(ftpPath);
        for (FTPFile f : listFiles) {
            if (ff.accept(f) && f.isFile()) {
                files.add(ftpPath + "/" + f.getName());
            } else if (f.isDirectory() && !(f.getName().equals(".") || f.getName().equals(".."))) {
                files.addAll(listFiles(ftpPath + "/" + f.getName(), ff, recurse));
            }
        }
        return files;
    }

   

    public void downloadFiles(String ftpPath, FTPFileFilter ff, String outdir, boolean recurse) throws Exception {
        List<String> files = listFiles(ftpPath, ff, recurse);
        // client.enterLocalPassiveMode(); // uncomment if server is non local.
        this.ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
        for (String f : files) {
            log("downloading file : " + f);
            String filename = f.substring(f.lastIndexOf("/") + 1);
            String dir         = f.substring(0, f.lastIndexOf("/") > 0 ? f.lastIndexOf("/") : 0);

            File file = new File(outdir.replaceAll("/", File.separator) + File.separator + filename);
            try (OutputStream outfile = new BufferedOutputStream(new FileOutputStream(file))) {
                this.ftpClient.changeWorkingDirectory(dir);
                this.ftpClient.retrieveFile(filename, outfile);
            }

        }
    }

    public void connect(String username, String password) throws Exception {
        FTPClient client = new FTPClient();
        for (int i = 0; i < 5; i++) { // try five times
            client.connect(host, port);
            if (client.isConnected()) {
                break;
            }
        }
        if(!client.isConnected()) throw new RuntimeException("Unable to connect to host :" + this.host);
        client.login(username, password);
        this.ftpClient = client;
        printStatistics();
    }

    public void disconnect() {
        try {
            if (this.ftpClient != null && this.ftpClient.isConnected()) {
                this.ftpClient.disconnect();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
   
    private void printStatistics() {
        if (ftpClient == null)
            throw new NullPointerException("FTPClient cannot be null.");
        if (!ftpClient.isConnected())
            throw new RuntimeException("FTPClient should be connected to remote peer.");
        log(String.format("%-30s : %s", "isConnected", ftpClient.isConnected()));
        log(String.format("%-30s : %s", "isAvailable", ftpClient.isAvailable()));
        log(String.format("%-30s : %s", "isRemoteVerificationEnabled", ftpClient.isRemoteVerificationEnabled()));
        log(String.format("%-30s : %s", "isStrictMultilineParsing", ftpClient.isStrictMultilineParsing()));
        log(String.format("%-30s : %s", "isUseEPSVwithIPv4", ftpClient.isUseEPSVwithIPv4()));
    }

    private static void log(String msg) {
        System.out.println(msg);
    }

}

Here is simple main class to test.

package com;

import java.io.IOException;
import java.util.List;

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

import com.mm.ftpclient.FtpClientHelper;
import com.mm.ftpclient.FtpFilter;

public class Main {

    public static void main(String[] args) throws Exception {
        System.out.println("testing ftp client .................");
        FTPFileFilter filter = FtpFilter.andFilter(FtpFilter.FILES, FtpFilter.startsWithFilter("cdr", "cmr"),
                FtpFilter.endsWithFilter(".csv"));

        FtpClientHelper f = new FtpClientHelper("127.0.0.1");
        f.connect("demo", "demo");
        try {
            listFiles(f);
            f.downloadFiles("/myfiles", filter, "C:\\test_ftp\\download", true);           
        } finally {
            f.disconnect();
        }
        System.out.println("done..................");

    }

    private static void listFiles(FtpClientHelper f) throws IOException {
        List<String> files = f.listFiles("/myfiles", null, true);
        System.out.println("----------------------------------");
        for (String file : files) {
            System.out.println(file);
        }
        System.out.println("----------------------------------");
    }
}


The only dependency to run the above code is commons-net jar.
gradle co-ordinates - compile('commons-net:commons-net:3.3')

To test the above code, we can install the FreeFTPd server locally from
http://www.freesshd.com/?ctt=download .