How do I delete file from FTP server?

By Wayan in Apache Commons, Commons Net 0 Comment

This example demonstrates how to delete file from FTP server.

package org.kodejava.commons.net;

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

import java.io.IOException;

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

        try {
            client.connect("ftp.example.com");
            client.login("demo", "password");

            // Delete file on the FTP server. When the FTP delete
            // process completes, it returns true.
            String filename = "data.txt";
            boolean deleted = client.deleteFile(filename);
            if (deleted) {
                System.out.printf("File %s was deleted...", filename);
            } else {
                System.out.println("No file was deleted...");
            }

            client.logout();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                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 get a list of files from FTP server?

By Wayan in Apache Commons, Commons Net 1 Comment

This example demonstrates how to retrieve a list of files from FTP server. First we create an instance of org.apache.commons.net.ftp.FTPClient. Connect to the FTP server and login with your username and password.

The listFiles() method of the FTPClient return the list of filenames contained in the current working directory. null if the list could not be obtained. If there are no filenames in the directory, a zero-length array is returned.

package org.kodejava.commons.net;

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

import java.io.IOException;

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

        try {
            client.connect("ftp.example.com");
            client.login("demo", "password");

            if (client.isConnected()) {
                // Obtain a list of filenames in the current working
                // directory. When no file is found, an empty array will
                // be returned.
                String[] names = client.listNames();
                for (String name : names) {
                    System.out.println("Name = " + name);
                }

                FTPFile[] ftpFiles = client.listFiles();
                for (FTPFile ftpFile : ftpFiles) {
                    // Check if FTPFile is a regular file
                    if (ftpFile.getType() == FTPFile.FILE_TYPE) {
                        System.out.printf("FTPFile: %s; %s%n",
                            ftpFile.getName(),
                            FileUtils.byteCountToDisplaySize(ftpFile.getSize()));
                    }
                }
            }
            client.logout();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                client.disconnect();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Here is the example result of our code:

Name = example.html
Name = Touch.dat
FTPFile: examples.html; 1 bytes
FTPFile: Touch.dat; 0 bytes

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>commons-net</groupId>
        <artifactId>commons-net</artifactId>
        <version>3.10.0</version>
    </dependency>
    <dependency>
        <groupId>commons-io</groupId>
        <artifactId>commons-io</artifactId>
        <version>2.14.0</version>
    </dependency>
</dependencies>

Maven Central Maven Central

How do I upload file to FTP server?

By Wayan in Apache Commons, Commons Net 37 Comments

This example demonstrates how to upload file to FTP server.

package org.kodejava.commons.net;

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

import java.io.IOException;
import java.io.InputStream;

public class FTPUploadDemo {
    public static void main(String[] args) {
        FTPClient client = new FTPClient();
        String filename = "data.txt";

        // Read the file from the resources folder.
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        try (InputStream is = classLoader.getResourceAsStream(filename)) {
            client.connect("ftp.example.com");
            boolean login = client.login("demo", "password");
            if (login) {
                System.out.println("Login success...");

                // Store file to server
                client.storeFile(filename, is);
                client.logout();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                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 download file from FTP server?

By Wayan 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 Wayan 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 Wayan 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 Wayan 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 Wayan 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

What is @SuppressWarnings annotation?

By Wayan in Basic, Core API 0 Comment

The @SuppressWarnings annotation tells the compiler to suppress the warning messages it normally shows during compilation time. It has some level of suppression to be added to the code, these level including: all, deprecation, fallthrough, finally, path, serial and unchecked.

package org.kodejava.basic;

import java.util.Calendar;
import java.util.Date;

public class SuppressWarningsExample {
    @SuppressWarnings(value={"deprecation"})
    public static void main(String[] args) {
        Date date = new Date(2021, Calendar.OCTOBER, 3);

        System.out.println("date = " + date);
    }
}

In the example above if we don’t use @SuppressWarnings annotation the compiler will report that the constructor of the Date class called above has been deprecated.

How do I use @Override annotation?

By Wayan in Basic, Core API 0 Comment

We use the @Override annotation as part of method declaration. The @Override annotation is used when we want to override methods and want to make sure have overridden the correct methods.

As the annotation name we know that there should be the same method signature in the parent class to override. That means using this annotation let us know earlier when we are mistakenly override method that doesn’t exist in the base class.

package org.kodejava.basic;

public class OverrideExample {
    private String field;
    private String attribute;

    @Override
    public int hashCode() {
        return field.hashCode() + attribute.hashCode();
    }

    @Override
    public String toString() {
        return field + " " + attribute;
    }
}