How do I use Java NIO to copy file?

By Wayan in Core API, IO 0 Comment

The following code snippet show you how to copy a file using the NIO API. The NIO (New IO) API is in the java.nio.* package. It requires at least Java 1.4 because the API was first included in this version. The JAVA NIO is a block based IO processing, instead of a stream based IO which is the old version IO processing in Java.

package org.kodejava.io;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.channels.FileChannel;
import java.nio.ByteBuffer;

public class CopyFileExample {
    public static void main(String[] args) throws Exception {
        String source = "medical-report.txt";
        String destination = "medical-report-final.txt";

        FileInputStream fis = new FileInputStream(source);
        FileOutputStream fos = new FileOutputStream(destination);

        FileChannel inputChannel = fis.getChannel();
        FileChannel outputChannel = fos.getChannel();

        // Create a buffer with 1024 size for buffering data
        // while copying from source file to destination file.
        // To create the buffer here we used a static method
        // ByteBuffer.allocate()
        ByteBuffer buffer = ByteBuffer.allocate(1024);

        // Here we start to read the source file and write it
        // to the destination file. We repeat this process
        // until the read method of input stream channel return
        // nothing (-1).
        while (true) {
            // Read a block of data and put it in the buffer
            int read = inputChannel.read(buffer);

            // Did we reach the end of the channel? if yes
            // jump out the while-loop
            if (read == -1) {
                break;
            }

            // flip the buffer
            buffer.flip();

            // write to the destination channel and clear the buffer.
            outputChannel.write(buffer);
            buffer.clear();
        }
    }
}

How do I split a string?

By Wayan in Core API, Lang Package 0 Comment

Prior to Java 1.4 we use java.util.StringTokenizer class to split a tokenized string, for example a comma separated string. Starting from Java 1.4 and later the java.lang.String class introduce a String.split(String regex) method that simplify this process.

Below is a code snippet how to do it.

package org.kodejava.lang;

import java.util.Arrays;

public class StringSplit {
    public static void main(String[] args) {
        String data = "1,Diego Maradona,Footballer,Argentina";
        String[] items = data.split(",");

        // Iterates the array to print it out.
        for (String item : items) {
            System.out.println("item = " + item);
        }

        // Or simply use Arrays.toString() when print it out.
        System.out.println("item = " + Arrays.toString(items));
    }
}

The result of the code snippet:

item = 1
item = Diego Maradona
item = Footballer
item = Argentina
item = [1, Diego Maradona, Footballer, Argentina]

How do I execute other applications from Java?

By Wayan in Core API, Lang Package 0 Comment

The following program allows you to run / execute other application from Java using the Runtime.exec() method.

package org.kodejava.lang;

import java.io.IOException;

public class RuntimeExec {
    public static void main(String[] args) {
        //String command = "/Applications/Safari.app/Contents/MacOS/Safari";
        String command = "explorer.exe";

        try {
            Process process = Runtime.getRuntime().exec(new String[]{command});
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I get path / classpath separator?

By Wayan in Core API, Lang Package 0 Comment

OS platform has a different symbol used for path separator. Path separator is a symbol that separate one path element from the other. In Windows the path separator is a semicolon symbol (;), you have something like:

.;something.jar;D:/libs/commons.jar

While in Linux based operating systems the path separator is a colon symbol (:), it looks like:

.:something.jar:/libs/commons.jar

To obtain the path separator you can use the following code.

package org.kodejava.lang;

import java.util.Properties;

public class PathSeparator {
    public static void main(String[] args) {
        // Get System properties
        Properties properties = System.getProperties();

        // Get the path separator which is unfortunately
        // using a different symbol in different OS platform.
        String pathSeparator = properties.getProperty("path.separator");
        System.out.println("pathSeparator = " + pathSeparator);
    }
}

How do I make a centered JFrame?

By Wayan in Swing 0 Comment

If you have a JFrame in your Java Swing application and want to center its position on the screen you can use the following code snippets.

The first way is to utilize java.awt.Toolkit class to get the screen size. The getScreenSize() method return a java.awt.Dimension from where we can get the width and height of the screen. Having this values in hand we can calculate the top left position of our JFrame as shown in step 2 of the code below.

package org.kodejava.swing;

import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import java.awt.Dimension;
import java.awt.Toolkit;

public class CenteredJFrame extends JFrame {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            // 1. Get the size of the screen
            Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

            CenteredJFrame frame = new CenteredJFrame();
            frame.setTitle("Centered JFrame");
            frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            frame.setSize(500, 500);

            // 2. Calculates the position where the CenteredJFrame
            // should be paced on the screen.
            int x = (screenSize.width - frame.getWidth()) / 2;
            int y = (screenSize.height - frame.getHeight()) / 2;
            frame.setLocation(x, y);
            frame.setVisible(true);
        });
    }
}

The second way which is better and simpler is to use the setLocationRelativeTo(Component) method. According to the Java API documentation of this method: If the component is null, or the GraphicsConfiguration associated with this component is null, the window is placed in the center of the screen.

If you call the JFrame.pack() method. The method should be called before the setLocationRelativeTo() method.

So we can rewrite the code above like this:

package org.kodejava.swing;

import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;

public class CenteredJFrameSecond {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            CenteredJFrame frame = new CenteredJFrame();
            frame.setTitle("Centered JFrame");
            frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            frame.setSize(500, 500);

            // Place the window in the center of the screen.
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }
}