How do I launch user-default web browser?

The code below show you how to browse a website using the user’s default web browser. To get the default web browser you can use the Desktop class browse(URI uri) method call.

package org.kodejava.awt;

import java.awt.Desktop;
import java.io.IOException;
import java.net.URI;

public class RunningDefaultBrowser {
    public static void main(String[] args) {
        URI uri = URI.create("https://kodejava.org");
        try {
            // Get Desktop instance of the current browser context. An 
            // UnsupportedOperationException will be thrown if the 
            // platform doesn't support Desktop API. 
            Desktop desktop = Desktop.getDesktop();

            // Browse the uri using user's default web browser.
            desktop.browse(uri);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I get and display an image in Applet?

To display an image in an applet we first need to obtain the image object itself. A call to applet’s getImage(URL url, String name) method help us to create an image object from the specified URL of the image.

For displaying the image on the applet’s screen we draw it in the paint() method using Graphics.drawImage() method.

package org.kodejava.applet;

import java.applet.Applet;
import java.awt.*;

public class AppletGetImage extends Applet {
    private Image logo;

    @Override
    public void init() {
        // Get an Image object that can be painted on the Applet
        // screen. We need to supply the URL of the document as
        // the base location of the image and the location of the
        // image relative the base URL. 
        logo = getImage(getDocumentBase(), "/images/logo.png");
    }

    @Override
    public void paint(Graphics g) {
        g.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
        g.drawImage(logo, 10, 10, this);
    }
}
** Deprecated: The Applet API is deprecated since JDK 9, no replacement.

How do I get Applet’s document URL?

The code snippet below show you how to get the URL of the document (HTML, JSP, etc.) where the Applet is embedded. To obtain this document URL we use the getDocumentBase() method call provided by the Applet class.

In the paint() method below we use the getDocumentBase() to create a URL as a link to an image to be displayed by our applet.

package org.kodejava.applet;

import java.applet.Applet;
import java.awt.*;

public class AppletDocumentBase extends Applet {
    private Image logo;

    @Override
    public void init() {
        // Locates logo image base on the URL of the document
        // where the Applet is embedded which is returned by
        // the getDocumentBase() method call.
        //
        // eg. http://localhost:8080/images/logo.jpg
        logo = getImage(getDocumentBase(), "/images/logo.png");
    }

    @Override
    public void paint(Graphics g) {
        g.setColor(Color.black);
        g.drawRect(0, 0, getWidth() - 1, getHeight() - 1);

        // Draw the logo image on the Applet surface.
        g.drawImage(logo, 10, 10, this);
    }
}
** Deprecated: The Applet API is deprecated since JDK 9, no replacement.

How do I move directory to another directory with its entire contents?

Below is an example to move one directory with all its child directory and files to another directory. We can use the FileUtils.moveDirectory() method to simplify the process.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;

public class DirectoryMove {
    public static void main(String[] args) {
        String source = "F:/Temp/source";
        File srcDir = new File(source);

        String destination = "F:/Temp/target";
        File destDir = new File(destination);

        try {
            // Move the source directory to the destination directory.
            // The destination directory must not exist prior to the
            // move process.
            FileUtils.moveDirectory(srcDir, destDir);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.16.1</version>
</dependency>

Maven Central

How do I copy directory with all its contents to another directory?

To copy a directory with the entire child directories and files we can use a handy method provided by the Apache Commons IO FileUtils.copyDirectory(). This method accepts two parameters, the source directory and the destination directory. The source directory should be available while if the destination directory doesn’t exist, it will be created.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;

public class DirectoryCopy {
    public static void main(String[] args) {
        // An existing directory to copy.
        String source = "F:/Temp/source";
        File srcDir = new File(source);

        // The destination directory to copy to. This directory
        // doesn't exist and will be created during the copy
        // directory process.
        String destination = "F:/Temp/target";
        File destDir = new File(destination);

        try {
            // Copy source directory into destination directory
            // including its child directories and files. The
            // destination directory will be created if it does
            // not exist. This copy processes also preserve the
            // date information of the file.
            FileUtils.copyDirectory(srcDir, destDir);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.16.1</version>
</dependency>

Maven Central

How do I copy a URL into a file?

The code snippet below shows you how to use the FileUtils.copyURLToFile(URL, File) method of the Apache Commons IO library to help you to copy the contents of a URL directly into a file.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URI;
import java.net.URL;

public class URLToFile {
    public static void main(String[] args) {
        try {
            URL url = URI.create("https://www.google.com").toURL();
            File destination = new File("google.html");

            // Copy bytes from the URL to the destination file.
            FileUtils.copyURLToFile(url, destination);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.16.1</version>
</dependency>

Maven Central

How do I set the maximum rows to read in a query?

If you want to limit the result of your query, you can call the Statement.setMaxRows(int max) method. This call will allow the ResultSet object contains a maximum number of records specified in the parameter of the setMaxRows method.

Another way to limit the number of data returned in a query is to use the database-specific command such as the MySQL limit command.

package org.kodejava.jdbc;

import java.sql.*;

public class SetMaxRowExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            Statement statement = connection.createStatement();

            // Executes an SQL query to get the total number of data
            // in product table.
            String query = "select count(*) from product";
            ResultSet rs = statement.executeQuery(query);

            while (rs.next()) {
                System.out.println("Total Products: " + rs.getInt(1));
            }

            // Set the maximum row of data that can be stored in the
            // ResultSet.
            statement.setMaxRows(5);

            // Executes an SQL query to retrieve data from product
            // table.
            query = "select id, code, name, price from product";
            rs = statement.executeQuery(query);

            System.out.println("Data read after the MaxRows is set.");
            while (rs.next()) {
                System.out.println("ID: " + rs.getInt("id")
                                   + ", CODE: " + rs.getString("code")
                                   + ", NAME: " + rs.getString("name")
                                   + ", PRICE: " + rs.getBigDecimal("price"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

When running the code, we’ll see that only 5 records were read from the product table instead of 10 records. This is the result of setting the maximum rows in the Statement object.

Below is the output of our code.

Total Products: 9
Data read after the MaxRows is set.
ID: 1, CODE: P0000001, NAME: UML Distilled 3rd Edition, PRICE: 25.00
ID: 3, CODE: P0000003, NAME: PHP Programming, PRICE: 20.00
ID: 4, CODE: P0000004, NAME: Longman Active Study Dictionary, PRICE: 40.00
ID: 5, CODE: P0000005, NAME: Ruby on Rails, PRICE: 24.00
ID: 6, CODE: P0000006, NAME: Championship Manager, PRICE: 0.00

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central

How do I get free space of a drive or volume?

The getFreeSpaceKb(String path) method in the FileSystemUtils class can help you to calculate the free space of a drive or volume in kilobytes.

Beside using commons-io solution, you can use the File.getFreeSpace() method call provided in the Java 1.6 API. You can find an example of it in the following link: How do I get total space and free space of my disk?.

package org.kodejava.commons.io;

import org.apache.commons.io.FileSystemUtils;
import org.apache.commons.io.FileUtils;

import java.io.IOException;

public class DiskFreeSpace {
    public static void main(String[] args) {
        try {
            String path = "F:/Temp";
            long freeSpaceKB = FileSystemUtils.freeSpaceKb(path);
            long freeSpaceMB = freeSpaceKB / FileUtils.ONE_KB;
            long freeSpaceGB = freeSpaceKB / FileUtils.ONE_MB;

            System.out.println("Size of " + path + " = " + freeSpaceKB + " KB");
            System.out.println("Size of " + path + " = " + freeSpaceMB + " MB");
            System.out.println("Size of " + path + " = " + freeSpaceGB + " GB");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

An example result of the code above is:

Size of F:/Temp = 323413052 KB
Size of F:/Temp = 315833 MB
Size of F:/Temp = 308 GB

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.16.1</version>
</dependency>

Maven Central

How do I get printer or print service name?

This example show you how to get the printer or print service installed on your machine. To get the installed services we can use PrinterJob.lookupPrintServices() method call. This method return an array of PrintService objects. After that call PrintService.getName() method to get the print service name.

package org.kodejava.print;

import javax.print.PrintService;
import java.awt.print.PrinterJob;

public class PrinterName {
    public static void main(String[] args) {
        // Lookup for the available print services.
        PrintService[] printServices = PrinterJob.lookupPrintServices();

        // Iterates the print services and print out its name.
        for (PrintService printService : printServices) {
            String name = printService.getName();
            System.out.println("Name = " + name);
        }
    }
}

The program will print the installed print service on your machine.

Name = OneNote for Windows 10
Name = OneNote (Desktop)
Name = Microsoft XPS Document Writer
Name = Microsoft Print to PDF
Name = HP LaserJet P1005
Name = Fax

How do I clear a buffer using compact() method?

If you want to clear a buffer, but you want to keep the unread data in the buffer then you need to use the compact() method of the buffer. The compact() method will copy the unread data to the beginning of the buffer and set the position right after the unread data. The limit itself still have the value equals to the buffer capacity. The buffer will be ready to be written again without overwriting the unread data.

package org.kodejava.io;

import java.nio.CharBuffer;

public class BufferCompact {
    public static void main(String[] args) throws Exception {
        CharBuffer buffer = CharBuffer.allocate(64);
        buffer.put("Let's write some Java code! ");

        System.out.println("Position: " + buffer.position());
        System.out.println("Limit   : " + buffer.limit());

        // Read 10 chars from the buffer.
        buffer.flip();
        for (int i = 0; i < 10; i++) {
            System.out.print(buffer.get());
        }
        System.out.println();

        System.out.println("Position: " + buffer.position());
        System.out.println("Limit   : " + buffer.limit());

        // clear the buffer using compact() method.
        buffer.compact();
        System.out.println("Position: " + buffer.position());
        System.out.println("Limit   : " + buffer.limit());

        // Write and read some more data.
        buffer.put("Add some more data.");

        buffer.flip();
        while (buffer.hasRemaining()) {
            System.out.print(buffer.get());
        }
    }
}

The output of the code snippet above is:

Position: 28
Limit   : 64
Let's writ
Position: 10
Limit   : 28
Position: 18
Limit   : 64
e some Java code! Add some more data.