How do I download file from FTP server?

By I Wayan Saryada in Apache Commons, Commons Net 19 Comments

This example demonstrates how to download a file from FTP server. To download a file, we first connect to the FTP server and then login by supplying the username and password. To download the file we call retrieveFile() method of the FTPClient object. This method takes two parameters, the remote filename and an OutputStream of the local file where the download to be saved.

package org.kodejava.commons.net;

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

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class FTPDownloadDemo {
    public static void main(String[] args) {
        // The local filename and remote filename to be downloaded.
        String filename = "data.txt";

        FTPClient client = new FTPClient();
        try (OutputStream os = new FileOutputStream(filename)) {
            client.connect("ftp.example.com");
            boolean login = client.login("demo", "password");
            if (login) {
                System.out.println("Login success...");

                // Download file from FTP server.
                boolean status = client.retrieveFile(filename, os);
                System.out.println("status = " + status);
                System.out.println("reply  = " + client.getReplyString());
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

If the download process was success, you will see the following output printed:

status = true
reply  = 226 Transfer complete.

Maven Dependencies

<dependency>
    <groupId>commons-net</groupId>
    <artifactId>commons-net</artifactId>
    <version>3.10.0</version>
</dependency>

Maven Central

How do I connect to FTP server?

By I Wayan Saryada in Apache Commons, Commons Net 2 Comments

The File Transfer Protocol (FTP) is a standard network protocol used to transfer computer files between a client and server on a computer network. The example below shows you how to connect to an FTP server.

In this example we are using the FTPClient class of the Apache Commons Net library. To connect to the server, we need to provide the FTP server name. Login to the server can be done by calling the login() method of this class with a valid username and password. To logout we call the logout() method.

Let’s try the code snippet below:

package org.kodejava.commons.net;

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

import java.io.IOException;

public class FTPConnectDemo {
    public static void main(String[] args) {
        FTPClient client = new FTPClient();

        try {
            client.connect("ftp.example.com");

            // When login success, the login method returns true.
            boolean login = client.login("demo", "password");
            if (login) {
                System.out.println("Login success...");

                // When logout success, the logout method returns true.
                boolean logout = client.logout();
                if (logout) {
                    System.out.println("Logout from FTP server...");
                }
            } else {
                System.out.println("Login fail...");
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                // Closes the connection to the FTP server
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-net</groupId>
    <artifactId>commons-net</artifactId>
    <version>3.10.0</version>
</dependency>

Maven Central

How do I touch a file using Apache Commons IO?

By I Wayan Saryada in Apache Commons, Commons IO 0 Comment

This example demonstrates a touch command just like Unix touch command. If the file to be touched doesn’t exist, a new empty file will be created.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

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

public class TouchFileExample {
    public static void main(String[] args) {
        try {
            File file = new File("Touch.dat");

            // Touch the file. When the file does not exist, a new file will be
            // created. If the file exists, change the file timestamp.
            FileUtils.touch(file);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

Maven Central

How do I delete directory recursively?

By I Wayan Saryada in Apache Commons, Commons IO 0 Comment

Using the FileUtils.deleteDirectory() from the Apache Commons IO library, we can simplify the process of deleting directory and everything below it recursively.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

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

public class DeleteDirectory {
    public static void main(String[] args) {
        try {
            File directory = new File("F:/Temp");

            // Deletes a directory recursively. When a deletion process is failed, an
            // IOException will be thrown; that's why we catch the exception.
            FileUtils.deleteDirectory(directory);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

Maven Central

How do I create a human-readable file size?

By I Wayan Saryada in Apache Commons, Commons IO 0 Comment

This example demonstrates how to create a human-readable file size using the FileUtils class of the Apache Commons IO library. The byteCountToDisplaySize() method take the file size in bytes and return a human-readable display of the file size in bytes, kilobytes, megabytes, gigabytes, etc.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;

public class ReadableFileSize {
    public static void main(String[] args) {
        File file = new File("D:/Downloads/jdk-17_windows-x64_bin.exe");

        long size = file.length();
        String display = FileUtils.byteCountToDisplaySize(size);

        System.out.println("Name    = " + file.getName());
        System.out.println("Size    = " + size);
        System.out.println("Display = " + display);
    }
}

Here are the results of our program:

Name    = jdk-17_windows-x64_bin.exe
Size    = 159373640
Display = 151 MB

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

Maven Central