How do I get MAC address of a host?

By Wayan in Core API, Networking 4 Comments

Previously for obtaining a MAC address we need to use a native code as a solution. In JDK 1.6 a new method is added in the java.net.NetworkInterface class, this method is getHardwareAddress().

package org.kodejava.net;

import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.net.UnknownHostException;

public class MacAddress {
    public static void main(String[] args) {
        try {
            // InetAddress address = InetAddress.getLocalHost();
            InetAddress address = InetAddress.getByName("192.168.0.105");

            /*
             * Get NetworkInterface for the current host and then read
             * the hardware address.
             */
            NetworkInterface ni = NetworkInterface.getByInetAddress(address);
            if (ni != null) {
                byte[] mac = ni.getHardwareAddress();
                if (mac != null) {
                    /*
                     * Extract each array of mac address and convert it
                     * to hexadecimal with the following format
                     * 08-00-27-DC-4A-9E.
                     */
                    for (int i = 0; i < mac.length; i++) {
                        System.out.format("%02X%s", mac[i], (i < mac.length - 1) ? "-" : "");
                    }
                } else {
                    System.out.println("Address doesn't exist or is not accessible.");
                }
            } else {
                System.out.println("Network Interface for the specified address is not found.");
            }
        } catch (UnknownHostException | SocketException e) {
            e.printStackTrace();
        }
    }
}

How do I convert milliseconds value to date?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

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

public class MillisecondsToDate {
    public static void main(String[] args) {
        // Create a DateFormatter object for displaying date information.
        DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy hh:mm:ss.SSS");

        // Get date and time information in milliseconds
        long now = System.currentTimeMillis();

        // Create a calendar object that will convert the date and time value
        // in milliseconds to date. We use the setTimeInMillis() method of the
        // Calendar object.
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(now);

        System.out.println(now + " = " + formatter.format(calendar.getTime()));
    }
}

The output of the code snippet above is:

1632868662762 = 29/09/2021 06:37:42.762

How do I send an email with attachment?

By Wayan in Mail 10 Comments

In this example we create a small program to send email with a file attachment. To send message with attachment we need to create an email with javax.mail.Multipart object which basically will contain the email text message and then add a file to the second block, which both of them is an object of javax.mail.internet.MimeBodyPart. In this example we also use the javax.activation.FileDataSource.

package org.kodejava.mail;

import javax.activation.DataHandler;
import javax.activation.FileDataSource;
import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
import java.util.Date;
import java.util.Properties;

public class SendEmailWithAttachment {
    public static void main(String[] args) {
        SendEmailWithAttachment demo = new SendEmailWithAttachment();
        demo.sendEmail();
    }

    public void sendEmail() {
        // Defines the E-Mail information.
        String from = "[email protected]";
        String to = "[email protected]";
        String subject = "Important Message";
        String bodyText = "This is a important message with attachment.";

        // The attachment file name.
        String attachmentName = "data.txt";

        // Creates a Session with the following properties.
        Properties props = new Properties();
        props.put("mail.smtp.host", "smtp.gmail.com");
        props.put("mail.transport.protocol", "smtp");
        props.put("mail.smtp.starttls.enable", "true");
        props.put("mail.smtp.port", "587");
        props.put("mail.smtp.ssl.protocols", "TLSv1.2");
        Session session = Session.getDefaultInstance(props);

        try {
            InternetAddress fromAddress = new InternetAddress(from);
            InternetAddress toAddress = new InternetAddress(to);

            // Create an Internet mail msg.
            MimeMessage msg = new MimeMessage(session);
            msg.setFrom(fromAddress);
            msg.setRecipient(Message.RecipientType.TO, toAddress);
            msg.setSubject(subject);
            msg.setSentDate(new Date());

            // Set the email msg text.
            MimeBodyPart messagePart = new MimeBodyPart();
            messagePart.setText(bodyText);

            // Set the email attachment file
            FileDataSource fileDataSource = new FileDataSource(attachmentName);

            MimeBodyPart attachmentPart = new MimeBodyPart();
            attachmentPart.setDataHandler(new DataHandler(fileDataSource));
            attachmentPart.setFileName(fileDataSource.getName());

            // Create Multipart E-Mail.
            Multipart multipart = new MimeMultipart();
            multipart.addBodyPart(messagePart);
            multipart.addBodyPart(attachmentPart);

            msg.setContent(multipart);

            // Send the msg. Don't forget to set the username and password
            // to authenticate to the mail server.
            Transport.send(msg, "kodejava", "password");
        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependencies>
    <dependency>
        <groupId>javax.mail</groupId>
        <artifactId>javax.mail-api</artifactId>
        <version>1.5.6</version>
    </dependency>
    <dependency>
        <groupId>javax.mail</groupId>
        <artifactId>mail</artifactId>
        <version>1.4.7</version>
    </dependency>
</dependencies>

Maven Central Maven Central

How do I split a string using Scanner class?

By Wayan in Core API, Util Package 0 Comment

Instead of using the StringTokenizer class or the String.split() method we can use the java.util.Scanner class to split a string.

package org.kodejava.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ScannerTokenDemo {
    public static void main(String[] args) {
        // This file contains some data as follows:
        // a, b, c, d
        // e, f, g, h
        // i, j, k, l
        File file = new File("data.txt");
        try {
            // Here we use the Scanner class to read file content line-by-line.
            Scanner scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();

                // From the above line of code we got a line from the file
                // content. Now we want to split the line with comma as the 
                // character delimiter.
                Scanner lineScanner = new Scanner(line);
                lineScanner.useDelimiter(",");
                while (lineScanner.hasNext()) {
                    // Get each split data from the Scanner object and print
                    // the value.
                    String part = lineScanner.next();
                    System.out.print(part + ", ");
                }                
                System.out.println();
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}

How do I read file line by line using java.util.Scanner class?

By Wayan in Core API, Util Package 0 Comment

Here is a compact way to read file line by line using the java.util.Scanner class.

package org.kodejava.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ScannerReadFile {
    public static void main(String[] args) {
        // Create an instance of File for data.txt file.
        File file = new File("README.md");
        try {
            // Create a new Scanner object which will read the data
            // from the file passed in. To check if there are more 
            // line to read from it, we call the scanner.hasNextLine() 
            // method. We then read line one by one till all lines 
            // is read.
            Scanner scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                System.out.println(line);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}