Steps:-

1. Download this commons-net.jar file

2. Extract the zip file

3. Copy the Jar file

4. Place the file in lib folder of your project.

5. Right click on the project

6. On left side of list, click on "Java Build Path"

7. Click on Libraries tab and Click on "Add Jar"

8. Browse the Commons-net.jar file and click on insert

Try this:

1. Download the "commons-net-3.9.0-bin.zip" from https://commons.apache.org/proper/commons-net/download_net.cgi
2. Extract the zip and using Android Studio place the "commons-net-3.9.0.jar" file into your ProjectName -> App -> Libs folder
3. Right click in the file and select at the bottom "Add As Library"

I didn't add anything into gradle file

I think you're correct. This is a bug in FTPClient.

socket.getInetAddress() is documented to throw NullPointerException if the socket is not open. This is called right after we call socket.close().

Found it!

The thing is you want to enter passive mode after you connect, but before you log in. Your code returns nothing for me, but this works for me:

import org.apache.commons.net.ftp.FTPClient;
import java.io.IOException;
import org.apache.commons.net.ftp.FTPFile;

public class BasicFTP {

    public static void main(String[] args) throws IOException {
        FTPClient client = new FTPClient();
        client.connect("c64.rulez.org");
        client.enterLocalPassiveMode();
        client.login("anonymous", "");
        FTPFile[] files = client.listFiles("/pub");
        for (FTPFile file : files) {
            System.out.println(file.getName());
        }
    }
}

Gives me this output:

c128
c64
c64.hu
incoming
plus4

I checked your code, it works. I've only changed file type declaration to binary, which may be not needed for XML files. Here's my complete code for reference:

package apachenet.ftp;

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

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

public class App {
    public static void main( String[] args ) {
        FTPClient client = new FTPClient(); 
        FileInputStream fis = null;
        try {
            client.connect(/*Util.getProductsXMLFTPServer()*/"127.0.0.1");
            client.login(/*Util.getProductsXMLFTPUser()*/"pwyrwinski", 
                    /*Util.getProductsXMLFTPPassword()*/"secret");
            client.setFileType(FTP.BINARY_FILE_TYPE); // optional
            fis = new FileInputStream(
                    new File(/* Util.getProductsXMLFTPInputFilePath() */"/home/pwyrwinski", 
                            /* Util.getProductsXMLFTPOutputFileName() */"img.png"));
            client.changeWorkingDirectory(/*Util.getProductsXMLFTPUploadPath()*/ "someDir");


            client.storeFile(/*Util.getProductsXMLFTPOutputFileName()*/"img_bis.png", fis);
            client.logout();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fis != null) {
                    fis.close();
                }
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

As you can see it's roughly the same as yours. Util class calls are replaced with raw data.

When I ran it, file /home/pwyrwinski/img.png was uploaded to {FTP_USER_ROOT}/someDir directory on ftp server with name changed to img_bis.png. I assume this is exactly what you wanted to achieve.

Let's go back to your problem.

1. Try to check what is returned from Util.getProductsXMLFTPUploadPath() call. My guess is it's not what you're expecting - so debug it in your IDE or print it to the console.
2. Check if path returned from Util.getProductsXMLFTPUploadPath() call starts with slash, it shouldn't.

UPDATE 1. Does direcory /home/domainname/public_html/guest exist on server?

Add following method to your class:

private static void showServerReply(FTPClient ftpClient) {
    String[] replies = ftpClient.getReplyStrings();
    if (replies != null && replies.length > 0) {
        for (String aReply : replies) {
            System.out.println("SERVER: " + aReply);
        }
    }
}

and call it after every ftp-client's method call. This will give you codes and descriptions of every command result. I suspect client.changeWorkingDirectory(...) ends with error, probably: 550 Permission Denied (or No such file or folder).

Next modification will be:

client.login(Util.getProductsXMLFTPUser(), Util.getProductsXMLFTPPassword());
System.out.println(client.printWorkingDirectory()); // added this line!

this will tell us what is current working directory after login in.

Please post your results.

Each FTP server has a different file list layout (yes, it's not part of the FTP standard, it's dumb), and so you have to use the correct FTPFileEntryParser, either by specifying it manually, or allowing CommonsFTP to auto-detect it.

Auto-detection usually works fine, but sometimes it doesn't, and you have to specify it explicitly, e.g.

FTPClientConfig conf = new FTPClientConfig(FTPClientConfig.SYST_UNIX);

FTPClient client = FTPClient();
client.configure(conf);

This explicitly sets the expected FTP server type to UNIX. Try the various types, see how it goes. I tried finding out myself, but ftp.belnet.be is refusing my connections :(

The dependency declaration looks wrong. The correct dependency for Apache Commons Net 3.11.1 is

<dependency>
    <groupId>commons-net</groupId>
    <artifactId>commons-net</artifactId>
    <version>3.11.1</version>
</dependency>