This article implements Java code examples that show how to connect and identify yourself to an FTP server using the Apache Commons Net. Make sure that the commons-net.jar file exists in your project's classpath.

The net.ftp.FTPClient provides the necessary basis for interacting with the server via the FTP protocol. To connect to the server, use this method:

void connect(String server, int port): The server can be set with the hostname or IP address, and the port is a number that is used to listen for incoming connections for a given application. FTP uses port 21.

After connecting, use this method to identify yourself:

boolean login(String username, String password): this method returns true if the identification was successful, otherwise false.

A response from the FTP server must be obtained after calling the connect():

int responseFTP = clientFTP.getReplyCode(); 
if (!reponseFTP.isPositiveCompletion(replyCode)) {
 // The operation failed. The server denies
 //the connection or rejects the 
 return operation; 
}

After each method call, the server returns messages. The following method displays messages from the server:

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

Here is the complete code that encompasses login, identification and verification:

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

public class FTPConnectionLogin {
 
 private static void serverresponse(FTPClient ftpClient) {
 String[] responses = ftpClient.getReplyStrings(); 
 if (answers != null & & answers.length > 0) {
 for (String response: responses) {
 System.out.println("SERVER: " + response); 
 }
 }
 }
 
 public static void main(String[] args) {
 String server = "serveraddress"; 
 int port = 21; 
 String username = "username"; 
 String password = "password"; 
 FTPClient ftpClient = new FTPClient(); 
 try {
 ftpClient.connect(server, port); 
 serverresponse(ftpClient); 
 int response = ftpClient.getReplyCode(); 
 if (! FTPReply.isPositiveCompletion(response)) {
 System.out.println("Operation failed. Server Answer: " + answer); 
 return; 
 }
 boolean status = ftpClient.login(username, password); 
 serverresponse(ftpClient); 
 if (!state) {
 System.out.println("Unable to access the server"); 
 return; 
 } else {
 System.out.println("Identification successful"); 
 }
 } catch (IOException ex) {
 System.out.println("An error during connection was detected"); 
 e.g.printStackTrace(); 
 }
 }
}

Compilation and execution:

SERVER: 220---------- Welcome to Pure-FTPd [privsep] ----------
SERVER: 220-You are user number 31 of 500 allowed.
SERVER: 220-Local time is now 06:02. Server port: 21.
SERVER: 220-This is a private system - No anonymous login
SERVER: 220 You will be disconnected after 3 minutes of inactivity.
SERVER: 230-OK. Current restricted directory is /
SERVER: 230-100 files used (1%) - authorized: 10000 files
SERVER: 230 5217 Kbytes used (0%) - authorized: 1536000 Kb
Successful identification