How do I store properties as XML file?

By Wayan in Core API, IO 0 Comment

In the previous example, How do I load properties from XML file? we read properties from XML file. Now it’s the turn on how to store the properties as XML file.

package org.kodejava.io;

import java.io.FileOutputStream;
import java.nio.charset.StandardCharsets;
import java.util.Properties;

public class PropertiesToXml {
    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        properties.setProperty("db.type", "mysql");
        properties.setProperty("db.url", "jdbc:mysql://localhost:3306/kodejava");
        properties.setProperty("db.username", "root");
        properties.setProperty("db.password", "");

        FileOutputStream fos = new FileOutputStream("db-config.xml");
        properties.storeToXML(fos, "Database Configuration", StandardCharsets.UTF_8);
    }
}

The saved XML file will look like the properties file below:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
    <comment>Database Configuration</comment>
    <entry key="db.type">mysql</entry>
    <entry key="db.password"></entry>
    <entry key="db.username">root</entry>
    <entry key="db.url">jdbc:mysql://localhost:3306/kodejava</entry>
</properties>

How do I load properties from XML file?

By Wayan in Core API, Util Package 0 Comment

Reading XML properties can be easily done using the java.util.Properties.loadFromXML() method. Just like reading the properties from a file that contains a key=value pairs, the XML file will also contain a key and value wrapped in the following XML format.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
<properties>
    <comment>Application Configuration</comment>
    <entry key="data.folder">D:\AppData</entry>
    <entry key="jdbc.url">jdbc:mysql://localhost/kodejava</entry>
</properties>

package org.kodejava.util;

import java.util.Properties;

public class LoadXmlProperties {
    public static void main(String[] args) {
        LoadXmlProperties demo = new LoadXmlProperties();
        try {
            Properties properties = demo.readProperties();

            //Display all properties information
            properties.list(System.out);

            // Read the value of data.folder and jdbc.url configuration
            String dataFolder = properties.getProperty("data.folder");
            System.out.println("data.folder = " + dataFolder);
            String jdbcUrl = properties.getProperty("jdbc.url");
            System.out.println("jdbc.url    = " + jdbcUrl);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private Properties readProperties() throws Exception {
        Properties properties = new Properties();
        properties.loadFromXML(getClass().getResourceAsStream("/configuration.xml"));
        return properties;
    }
}

The result of the code snippet above:

-- listing properties --
data.folder=D:\AppData
jdbc.url=jdbc:mysql://localhost/kodejava
data.folder = D:\AppData
jdbc.url    = jdbc:mysql://localhost/kodejava

How do I convert InputStream to String?

By Wayan in Core API, IO 1 Comment

This example will show you how to convert an InputStream into String. In the code snippet below we read a data.txt file, could be from common directory or from inside a jar file.

package org.kodejava.io;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class StreamToString {

    public static void main(String[] args) throws Exception {
        StreamToString demo = new StreamToString();

        // Get input stream of our data file. This file can be in
        // the root of your application folder or inside a jar file
        // if the program is packed as a jar.
        InputStream is = demo.getClass().getResourceAsStream("/student.csv");

        // Call the method to convert the stream to string
        System.out.println(demo.convertStreamToString(is));
    }

    private String convertStreamToString(InputStream stream) throws IOException {
        // To convert the InputStream to String we use the
        // Reader.read(char[] buffer) method. We iterate until the
        // Reader return -1 which means there's no more data to
        // read. We use the StringWriter class to produce the string.
        if (stream != null) {
            Writer writer = new StringWriter();

            char[] buffer = new char[1024];
            try (stream) {
                Reader reader = new BufferedReader(new InputStreamReader(stream,
                        StandardCharsets.UTF_8));
                int length;
                while ((length = reader.read(buffer)) != -1) {
                    writer.write(buffer, 0, length);
                }
            }
            return writer.toString();
        }
        return "";
    }
}

How do I convert string into InputStream?

By Wayan in Core API, IO 0 Comment

Here you will find how to convert string into java.io.InputStream object using java.io.ByteArrayInputStream class.

package org.kodejava.io;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class StringToStream {
    public static void main(String[] args) {
        String text = "Converting String to InputStream Example";

        // Convert String to InputStream using ByteArrayInputStream
        // class. This class constructor takes the string byte array
        // which can be done by calling the getBytes() method.
        InputStream stream = new ByteArrayInputStream(text.getBytes(StandardCharsets.UTF_8));
    }
}

How do I read system property as an integer?

By Wayan in Core API, Lang Package 0 Comment

The Integer.getInteger() methods allows us to easily read system property and convert it directly to Integer object. This method call the System.getProperty() method and then convert it to integer by calling the Integer.decode() method.

package org.kodejava.lang;

public class IntegerProperty {
    public static void main(String[] args) {
        // Add properties to the system. In this example we create a
        // dummy major and minor version for our application.
        System.setProperty("app.major.version", "2021");
        System.setProperty("app.minor.version", "9");

        // In the code below we use the Integer.getInteger() method to
        // read our application version from the value specified in the
        // system properties.
        Integer major = Integer.getInteger("app.major.version");
        Integer minor = Integer.getInteger("app.minor.version");
        System.out.println("App version = " + major + "." + minor);
    }
}

The output of the code snippet:

App version = 2021.9

How do I decode string to integer?

By Wayan in Core API, Lang Package 0 Comment

The static Integer.decode() method can be used to convert a string representation of a number into an Integer object. Under the cover this method call the Integer.valueOf(String s, int radix).

The string can start with the optional negative sign followed with radix specified such as 0x, 0X, # for hexadecimal value, 0 (zero) for octal number.

package org.kodejava.lang;

public class IntegerDecode {
    public static void main(String[] args) {
        String decimal = "10"; // Decimal
        String hex = "0XFF"; // Hex
        String octal = "077"; // Octal

        Integer number = Integer.decode(decimal);
        System.out.println("String [" + decimal + "] = " + number);

        number = Integer.decode(hex);
        System.out.println("String [" + hex + "] = " + number);

        number = Integer.decode(octal);
        System.out.println("String [" + octal + "] = " + number);
    }
}

The result of the code snippet above:

String [10] = 10
String [0XFF] = 255
String [077] = 63

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();
        }
    }
}