How do I execute external command and obtain the result?

By I Wayan Saryada in Core API, Lang Package 0 Comment

This example demonstrate how to execute an external command from Java and obtain the result of the command. Here we simply execute a Linux ls -al command on the current working directory and display the result.

package org.kodejava.lang;

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ProcessResult {
    public static void main(String[] args) {
        try {
            Process process = Runtime.getRuntime().exec("ls -al");

            // Wait for this process to finish or terminated
            process.waitFor();

            // Get process exit value
            int exitValue = process.exitValue();
            System.out.println("exitValue = " + exitValue);

            // Read the result of the ls -al command by reading the
            // process's input stream
            InputStreamReader is = new InputStreamReader(process.getInputStream());
            BufferedReader reader = new BufferedReader(is);
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Below is our program result:

exitValue = 0
total 64
drwxr-xr-x  20 wsaryada  staff   680 Aug  7 14:13 .
drwxr-xr-x   4 wsaryada  staff   136 Jun 18 00:33 ..
-rw-r--r--@  1 wsaryada  staff  6148 Jun 29 14:04 .DS_Store
-rw-r--r--   1 wsaryada  staff   267 May 19 20:47 .editorconfig
drwxr-xr-x  16 wsaryada  staff   544 Aug 10 08:34 .git
-rw-r--r--   1 wsaryada  staff  1535 May 19 20:47 .gitignore
drwxr-xr-x  15 wsaryada  staff   510 Aug 10 08:34 .idea
-rw-r--r--   1 wsaryada  staff  1313 May 19 20:47 LICENSE
-rw-r--r--   1 wsaryada  staff   101 May 19 20:47 README.md
drwxr-xr-x   5 wsaryada  staff   170 Jul 28 23:11 kodejava-basic
drwxr-xr-x   6 wsaryada  staff   204 Jun 30 14:22 kodejava-commons
drwxr-xr-x   6 wsaryada  staff   204 Jul 27 15:32 kodejava-lang-package
drwxr-xr-x@  5 wsaryada  staff   170 Jun 16 20:49 kodejava-mail
drwxr-xr-x   6 wsaryada  staff   204 Aug  7 17:22 kodejava-mybatis
drwxr-xr-x   5 wsaryada  staff   170 Jul 20 10:36 kodejava-poi
-rw-r--r--   1 wsaryada  staff   669 Jun  2 14:29 kodejava-project.iml
drwxr-xr-x   7 wsaryada  staff   238 Jun 26 21:52 kodejava-swing
drwxr-xr-x   6 wsaryada  staff   204 Aug  3 15:06 kodejava-util-package
drwxr-xr-x   6 wsaryada  staff   204 Jun 30 15:09 maven-helloworld
-rw-r--r--   1 wsaryada  staff  1622 Aug  7 14:13 pom.xml

How do I get the JFrame of a component?

By I Wayan Saryada in Swing 0 Comment

This code snippet gives an example on how to get the JFrame of a component. In this example we try to get the JFrame from a button action listener event. To get the JFrame we utilize the SwingUtilities.getRoot() method and this will return the root component of the component tree in out small program below which is a JFrame.

Beside getting the JFrame, in this program we also do small stuff like changing the frame background color by a random color every time a user presses the “Change Frame Color” button.

package org.kodejava.swing;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import java.awt.Color;
import java.awt.Component;
import java.awt.FlowLayout;
import java.awt.HeadlessException;

public class GetFrameDemo extends JFrame {
    public GetFrameDemo() throws HeadlessException {
        initialize();
    }

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

    private void initialize() {
        this.setSize(500, 500);
        this.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        this.setLayout(new FlowLayout(FlowLayout.CENTER));

        final JLabel rLabel = new JLabel("r: ");
        final JLabel gLabel = new JLabel("g: ");
        final JLabel bLabel = new JLabel("b: ");

        JButton button = new JButton("Change Frame Background Color");
        button.addActionListener(e -> {
            Component component = (Component) e.getSource();

            // Returns the root component for the current component tree
            JFrame frame = (JFrame) SwingUtilities.getRoot(component);

            int r = (int) (Math.random() * 255);
            int g = (int) (Math.random() * 255);
            int b = (int) (Math.random() * 255);

            rLabel.setText("r: " + r);
            gLabel.setText("g: " + g);
            bLabel.setText("b: " + b);

            frame.getContentPane().setBackground(new Color(r, g, b));
        });

        this.getContentPane().add(button);
        this.getContentPane().add(rLabel);
        this.getContentPane().add(gLabel);
        this.getContentPane().add(bLabel);
    }
}
Get Swing Root Component

Get Swing Root Component

How do I disable JFrame close button?

By I Wayan Saryada in Swing 0 Comment

To disable the close operation on a JFrame, when user click the close icon on the JFrame, we can set the value of the default close operation to WindowConstants.DO_NOTHING_ON_CLOSE.

package org.kodejava.swing;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.HeadlessException;

public class DisableCloseButtonDemo extends JFrame {
    public DisableCloseButtonDemo() throws HeadlessException {
        initialize();
    }

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

    private void initialize() {
        // WindowConstants.DO_NOTHING_ON_CLOSE tell JFrame instance to do
        // nothing when a window closing event occurs.
        this.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);

        JButton button = new JButton("Close");
        button.addActionListener(e -> System.exit(0));

        this.setLayout(new FlowLayout(FlowLayout.CENTER));
        this.setSize(new Dimension(500, 500));
        this.getContentPane().add(button);
    }
}

How do I get the path from where a class is loaded?

By I Wayan Saryada in Core API, Lang Package 0 Comment

This examples shows how to get a path name or location from where our class is loaded.

package org.kodejava.lang;

public class CodeSourceLocation {
    public static void main(String[] args) {
        CodeSourceLocation csl = new CodeSourceLocation();
        csl.getCodeSourceLocation();
    }

    private void getCodeSourceLocation() {
        // The location from where the class is loaded.
        System.out.println("Code source location: " +
            getClass().getProtectionDomain().getCodeSource().getLocation());
    }
}

The code snippet print the following output:

Code source location: file:/F:/Wayan/Kodejava/kodejava-example/kodejava-lang/target/classes/

How do I validate email address using regular expression?

By I Wayan Saryada in Core API, Lang Package 0 Comment

In this example we use the String‘s class matches() methods to match a string to be a valid email address based on the given regex.

This example also demonstrate the power of regular expression to validate an email address. Using regular expression makes it easier to validate data such as email address. After the code you’ll see the meaning of the regular expression used in the code below.

package org.kodejava.lang;

public class EmailAddressValidation {
    private static final String EMAIL_REGEX =
            "^[\\w-_\\.+]*[\\w-_\\.]\\@([\\w]+\\.)+[\\w]+[\\w]$";

    public static void main(String[] args) {
        EmailAddressValidation validator = new EmailAddressValidation();

        System.out.println("isValid = "
                + validator.isValidEmailAddress("[email protected]"));
        System.out.println("isValid = "
                + validator.isValidEmailAddress("[email protected]"));
        System.out.println("isValid = "
                + validator.isValidEmailAddress("[email protected]"));
        System.out.println("isValid = "
                + validator.isValidEmailAddress("user.domain.co.id"));
    }

    /**
     * Validates email address against email regular expression.
     *
     * @param email an email address to check
     * @return true if email address is valid otherwise return false.
     */
    private boolean isValidEmailAddress(String email) {
        return email.matches(EMAIL_REGEX);
    }
}

The first ^[\\w-_\\.+]. The ^ symbols means check the first character. This the regex processor that the email address should start with a word character formed of alphanumeric value (a-z 0-9) or it can also be a hyphen, underscore, dot or a plus symbol.

The second part, *[\\w-_\\.]. The * symbol means match the preceding zero or more times. As the first part, this tell the regex processor to check for another zero or more characters, and it can also contain hyphen, underscore and a dot.

The third part, \\@([\\w]+\\.)+. This check that email address should contain the @ symbol followed by one or more word separated by the dot symbol.

The last part is, [\\w]+[\\w]$, this check that after the last period there should be another word for the domain suffix such as the co.uk or co.id. And the $ ask that the email address should end by a word character.