How do I create a thread by implementing Runnable interface?

By Wayan in Core API, Lang Package 0 Comment

Here is the second way for creating a thread. We create an object that implements the java.lang.Runnable interface. For another example see How do I create a thread by extending Thread class?.

package org.kodejava.lang;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;

public class TimeThread implements Runnable {
    private final DateFormat df = new SimpleDateFormat("hh:mm:ss");

    // The run() method will be invoked when the thread of this runnable object
    // is started.
    @Override
    public void run() {
        while (true) {
            Calendar calendar = Calendar.getInstance();
            System.out.format("Now is: %s.%n", df.format(calendar.getTime()));

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        TimeThread time = new TimeThread();

        Thread thread = new Thread(time);
        thread.start();
    }
}

An example result of this code are:

Now is: 07:18:39.
Now is: 07:18:40.
Now is: 07:18:41.
Now is: 07:18:42.
Now is: 07:18:43.

How do I create a thread by extending Thread class?

By Wayan in Core API, Lang Package 0 Comment

There are two ways that we can use tho create a thread. First is by extending the java.lang.Thread class and the second way is by creating a class that implements the java.lang.Runnable interface. See How do I create a thread by implementing Runnable interface?

In this example we’ll extend the Thread class. To run a code in a thread we need to provide the run() method in our class. Let’s see the code below.

package org.kodejava.lang;

public class NumberPrinter extends Thread {
    private final String threadName;
    private final int delay;

    public NumberPrinter(String threadName, int delay) {
        this.threadName = threadName;
        this.delay = delay;
    }

    // The run() method will be invoked when the thread is started.
    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println("Thread [" + threadName + "] = " + i);

            try {
                Thread.sleep(delay);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        NumberPrinter printerA = new NumberPrinter("A", 1000);
        NumberPrinter printerB = new NumberPrinter("B", 750);

        printerA.start();
        printerB.start();
    }
}

The example result of our code is:

Thread [B] = 0
Thread [A] = 0
Thread [B] = 1
Thread [A] = 1
Thread [B] = 2
Thread [A] = 2
Thread [B] = 3
Thread [B] = 4
Thread [A] = 3
Thread [B] = 5
Thread [A] = 4
Thread [B] = 6
Thread [A] = 5
Thread [B] = 7
Thread [B] = 8
Thread [A] = 6
Thread [B] = 9
Thread [A] = 7
Thread [A] = 8
Thread [A] = 9

How do I compare two dates?

By Wayan in Core API, Util Package 0 Comment

In this example you’ll see the utilization of SimpleDateFormat class for comparing two dates for equality. We convert the date object into string using the DateFormat instance and then compare it using String.equals() method.

package org.kodejava.util;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class ComparingDate {
    public static void main(String[] args) {
        // Create a SimpleDateFormat instance with dd/MM/yyyy format
        DateFormat df = new SimpleDateFormat("dd/MM/yyyy");

        // Get the current date
        Date today = new Date();

        // Create an instance of calendar that represents a new year date
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DATE, 1);
        calendar.set(Calendar.MONTH, Calendar.JANUARY);
        calendar.set(Calendar.YEAR, 2021);

        String newYear = df.format(calendar.getTime());
        String now = df.format(today);

        // Using the string equals method we can compare the date.
        if (now.equals(newYear)) {
            System.out.println("Happy New Year!");
        } else {
            System.out.println("Have a nice day!");
        }
    }
}

How do I search for files recursively using Apache Commons IO?

By Wayan in Apache Commons, Commons IO 0 Comment

This example demonstrates how we can use the FileUtils class listFiles() method to search for a file specified by their extensions. We can also define to find the file recursively deep down into the subdirectories.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.util.Collection;

public class SearchFileRecursive {
    public static void main(String[] args) {
        File root = new File("F:/Wayan/Kodejava/kodejava-example");

        try {
            String[] extensions = {"xml", "java", "dat"};

            // Find files within a root directory and optionally its
            // subdirectories, which match an array of extensions. When the
            // extensions are null, all files will be returned.
            //
            // This method will return matched file as java.io.File
            Collection<File> files = FileUtils.listFiles(root, extensions, true);

            for (File file : files) {
                System.out.println("File = " + file.getAbsolutePath());
            }
        } catch (Exception 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 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