How do I create a NIO Buffer?

By Wayan in Core API, IO 0 Comment

This post show you how to use the java.nio buffer such as ByteBuffer, CharBuffer, DoubleBuffer, etc. To create a buffer you can use the allocate(int capacity) method. Each buffer object has the allocate(int capacity) method. You need to pass the value of the capacity of the buffer to be created when calling this method.

package org.kodejava.io;

import java.nio.*;

public class BufferAllocate {
    public static void main(String[] args) {
        ByteBuffer byteBuffer = ByteBuffer.allocate(64);
        CharBuffer charBuffer = CharBuffer.allocate(64);
        ShortBuffer shortBuffer = ShortBuffer.allocate(64);
        IntBuffer intBuffer = IntBuffer.allocate(64);
        LongBuffer longBuffer = LongBuffer.allocate(64);
        FloatBuffer floatBuffer = FloatBuffer.allocate(64);
        DoubleBuffer doubleBuffer = DoubleBuffer.allocate(64);
    }
}

How do I copy file using FileChannel class?

By Wayan in Core API, IO 2 Comments

The example below show you how to copy a file using the java.nio.channels.FileChannel class.

package org.kodejava.io;

import java.io.*;
import java.nio.channels.FileChannel;

public class FileCopy {
    public static void main(String[] args) {
        //// Define the source and target file
        File source = new File("D:/Temp/source.txt");
        File target = new File("D:/Temp/target.txt");

        // Create the source and target channel
        try (FileChannel sourceChannel = new FileInputStream(source).getChannel();
             FileChannel targetChannel = new FileOutputStream(target).getChannel()) {

            // Copy data from the source channel into the target channel
            targetChannel.transferFrom(sourceChannel, 0, sourceChannel.size());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

How do I create zip file in Servlet for download?

By Wayan in Servlet 15 Comments

The example below is a servlet that shows you how to create a zip file and send the generated zip file for user to download. The compressing process is done by the zipFiles method of this class.

For a servlet to work you need to configure it in the web.xml file of your web application which can be found after the code snippet below.

package org.kodejava.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

@WebServlet(urlPatterns = "/zipservlet")
public class ZipDownloadServlet extends HttpServlet {
    public static final String FILE_SEPARATOR = System.getProperty("file.separator");

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        try {
            // The path below is the root directory of data to be
            // compressed.
            String path = getServletContext().getRealPath("data");

            File directory = new File(path);
            String[] files = directory.list();

            // Checks to see if the directory contains some files.
            if (files != null && files.length > 0) {

                // Call the zipFiles method for creating a zip stream.
                byte[] zip = zipFiles(directory, files);

                // Sends the response back to the user / browser. The
                // content for zip file type is "application/zip". We
                // also set the content disposition as attachment for
                // the browser to show a dialog that will let user 
                // choose what action will he do to the content.
                ServletOutputStream sos = response.getOutputStream();
                response.setContentType("application/zip");
                response.setHeader("Content-Disposition", "attachment; filename=\"DATA.ZIP\"");

                sos.write(zip);
                sos.flush();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * Compress the given directory with all its files.
     */
    private byte[] zipFiles(File directory, String[] files) throws IOException {
        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
             ZipOutputStream zos = new ZipOutputStream(baos)) {
            byte[] bytes = new byte[2048];

            for (String fileName : files) {
                String path = directory.getPath() +
                        ZipDownloadServlet.FILE_SEPARATOR + fileName;
                try (FileInputStream fis = new FileInputStream(path);
                     BufferedInputStream bis = new BufferedInputStream(fis)) {

                    zos.putNextEntry(new ZipEntry(fileName));

                    int bytesRead;
                    while ((bytesRead = bis.read(bytes)) != -1) {
                        zos.write(bytes, 0, bytesRead);
                    }
                    zos.closeEntry();
                }
            }

            zos.close();
            return baos.toByteArray();
        }
    }
}

Maven dependencies

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
</dependency>

Maven Central

How do I create a console progress bar?

By Wayan in Core API, Lang Package 1 Comment

The code below demonstrates how to create a progress bar in a console program. The trick is to print the progress status using a System.out.print() and add a carriage return character ("\r") at the end of the string to return the cursor position to the beginning of the line and print the next progress status.

package org.kodejava.lang;

public class ConsoleProgressBar {
    public static void main(String[] args) {
        char[] animationChars = new char[]{'|', '/', '-', '\\'};

        for (int i = 0; i <= 100; i++) {
            System.out.print("Processing: " + i + "% " + animationChars[i % 4] + "\r");

            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println("Processing: Done!");
    }
}

How do I calculate process execution time in higher resolution?

By Wayan in Core API, Lang Package 0 Comment

This example demonstrates how to use the System.nanoTime() method to calculate processing execution time in higher resolution. The processing time calculated in nanoseconds resolution.

package org.kodejava.lang;

public class NanoSecondsTimerResolution {
    public static void main(String[] args) {
        // Get process execution start time in nanoseconds.
        long start = System.nanoTime();
        System.out.println("Process start... " + start);

        try {
            Thread.sleep(5000); // Simulate a long process.
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // Get process execution finish time in nanoseconds.
        long finish = System.nanoTime();
        System.out.println("Process finish... " + finish);

        // Calculate the process execution time.
        long execTime = finish - start;
        System.out.println("Processing time = " + execTime + "(ns)");
    }
}

How do I get the default print service?

By Wayan in Core API, Print Service 0 Comment

To look up the default print service we can use the javax.print.PrintServiceLookup class lookupDefaultPrintService() method.

package org.kodejava.print;

import javax.print.PrintService;
import javax.print.PrintServiceLookup;

public class GetPrinter {
    public static void main(String[] args) {
        // Gets the default print service for this environment. Null is returned when 
        // no default print service found.
        PrintService service = PrintServiceLookup.lookupDefaultPrintService();
        if (service != null) {
            String printServiceName = service.getName();
            System.out.println("Print Service Name = " + printServiceName);
        } else {
            System.out.println("No default print service found.");
        }
    }
}

The result of the code snippet above:

Print Service Name = HP LaserJet P1005

How do I add background image in JTextPane?

By Wayan in Swing 0 Comment

The example below demonstrate how to create a custom JTextPane component that have a background image.

package org.kodejava.swing;

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Objects;

public class TextPaneWithBackgroundImage extends JFrame {
    public TextPaneWithBackgroundImage() {
        initUI();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(
                () -> new TextPaneWithBackgroundImage().setVisible(true));
    }

    private void initUI() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        String imageFile = "/logo.png";
        CustomTextPane textPane = new CustomTextPane(imageFile);

        JScrollPane scrollPane = new JScrollPane(textPane);
        scrollPane.setPreferredSize(new Dimension(getWidth(), getHeight()));
        getContentPane().add(scrollPane);
        pack();
    }
}

/**
 * A custom text pane that have a background image. To customize the
 * JTextPane we override the paintComponent(Graphics g) method. We have
 * to draw an image before we call the super class paintComponent method.
 */
class CustomTextPane extends JTextPane {
    private final String imageFile;

    /**
     * Constructor of custom text pane.
     *
     * @param imageFile image file name for the text pane background.
     */
    CustomTextPane(String imageFile) {
        super();
        // To be able to draw the background image the component must
        // not be opaque.
        setOpaque(false);
        setForeground(Color.BLUE);

        this.imageFile = imageFile;
    }

    @Override
    protected void paintComponent(Graphics g) {
        try {
            // Load an image for the background image of out JTextPane.
            BufferedImage image = ImageIO.read(Objects.requireNonNull(
                    getClass().getResourceAsStream(imageFile)));
            g.drawImage(image, 0, 0, (int) getSize().getWidth(),
                    (int) getSize().getHeight(), this);
        } catch (IOException e) {
            e.printStackTrace();
        }

        super.paintComponent(g);
    }
}

JTextPane background image

How do I sort string of numbers in ascending order?

By Wayan in Core API, Util Package 2 Comments

In the following example we are going to sort a string containing the following numbers "2, 5, 9, 1, 10, 7, 4, 8" in ascending order, so we will get the result of "1, 2, 4, 5, 7, 8, 9, 10".

package org.kodejava.util;

import java.util.Arrays;

public class SortStringNumber {
    public static void main(String[] args) {
        // We have some string numbers separated by comma. First we
        // need to split it, so we can get each individual number.
        String data = "2, 5, 9, 1, 10, 7, 4, 8";
        String[] numbers = data.split(",");

        // Convert the string numbers into Integer and placed it into
        // an array of Integer.
        Integer[] intValues = new Integer[numbers.length];
        for (int i = 0; i < numbers.length; i++) {
            intValues[i] = Integer.parseInt(numbers[i].trim());
        }

        // Sort the number in ascending order using the
        // Arrays.sort() method.
        Arrays.sort(intValues);

        // Convert back the sorted number into string using the
        // StringBuilder object. Prints the sorted string numbers.
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < intValues.length; i++) {
            Integer intValue = intValues[i];
            builder.append(intValue);
            if (i < intValues.length - 1) {
                builder.append(", ");
            }
        }
        System.out.println("Before = " + data);
        System.out.println("After  = " + builder);
    }
}

When we run the program we will get the following output:

Before = 2, 5, 9, 1, 10, 7, 4, 8
After  = 1, 2, 4, 5, 7, 8, 9, 10

How do I turn on the Scroll Lock button?

By Wayan in AWT, Core API 0 Comment

The program below show you how to turn on the Scroll Lock button programmatically. Setting the locking state to Boolean.TRUE activate the Scroll Lock.

package org.kodejava.awt;

import java.awt.*;
import java.awt.event.KeyEvent;

public class TurnScrollLockOn {
    public static void main(String[] args) {
        // Gets the default toolkit.
        Toolkit toolkit = Toolkit.getDefaultToolkit();

        // Update the locking state for scroll lock button to true
        // will turn the scroll lock on.
        toolkit.setLockingKeyState(KeyEvent.VK_SCROLL_LOCK, Boolean.TRUE);
    }
}

How do I turn on the Num Lock button?

By Wayan in AWT, Core API 0 Comment

The example below show you how to activate the Num Lock button programmatically. Setting the locking state to Boolean.TRUE will turn the Num Lock on.

package org.kodejava.awt;

import java.awt.Toolkit;
import java.awt.event.KeyEvent;

public class TurnNumLockOn {
    public static void main(String[] args) {
        // Gets the default toolkit.
        Toolkit toolkit = Toolkit.getDefaultToolkit();

        // Update the locking state for num lock button to true
        // will turn the num lock on.
        toolkit.setLockingKeyState(KeyEvent.VK_NUM_LOCK, Boolean.TRUE);
    }
}