Create QR Codes in Java with the ZXing Library

 A QR code (short for Quick Response code) is a two-dimensional barcode that can be read by a smartphone or other device with a camera. QR codes are often used to store information such as URLs, text messages, or other data that can be quickly and easily read by a device.
In this we can see how to generate QR code using java.

To generate a QR code in Java, you can use a library called ZXing ("Zebra Crossing"). Here's a simple example of how to use it:

First, add the following dependency to your project's pom.xml file:

    <dependency>
       <groupId>com.google.zxing</groupId>
       <artifactId>core</artifactId>
       <version>3.4.0</version>
    </dependency>

Then, use the following code to generate a QR code for a text message:

    import java.awt.image.BufferedImage;
    import java.io.File;
    import java.io.IOException;
    import javax.imageio.ImageIO;

    import com.google.zxing.BarcodeFormat;
    import com.google.zxing.WriterException;
    import com.google.zxing.client.j2se.MatrixToImageWriter;
    import com.google.zxing.common.BitMatrix;
    import com.google.zxing.qrcode.QRCodeWriter;

    public class Main {
      public static void main(String[] args) throws WriterException, IOException {
        String text = "knjavaadda";  // The text to encode in the QR code
        int width = 300;  // The width of the QR code, in pixels
        int height = 300; // The height of the QR code, in pixels

        // Create the QR code writer
        QRCodeWriter qrCodeWriter = new QRCodeWriter();

        // Use the QR code writer to create a BitMatrix object representing the QR code
        BitMatrix bitMatrix = qrCodeWriter.encode(text, BarcodeFormat.QR_CODE, width, height);

        // Convert the BitMatrix object to a BufferedImage
        BufferedImage image = MatrixToImageWriter.toBufferedImage(bitMatrix);

        // Save the image to a file
        ImageIO.write(image, "PNG", new File("knjavaadda.png"));
      }
    }

This code will generate a QR code for the text "Hello, World!" and save it as a PNG file called "qr-code.png". You can customize the QR code by changing the text, size, and image format.

You can also generate QR codes for other types of data, such as URLs, email addresses, and phone numbers. Just pass the appropriate data to the encode method of the QRCodeWriter class. For example:

    String url = "https://knjavaadda.blogspot.com/";
    BitMatrix bitMatrix = qrCodeWriter.encode(url, BarcodeFormat.QR_CODE, width, height);

To customize the error correction level of the QR code, you can use the QRCodeWriter's setErrorCorrectionLevel method. The error correction level determines how much data can be recovered if the QR code is damaged. The possible values are L, M, Q, and H, corresponding to increasing levels of error correction. For example:

    qrCodeWriter.setErrorCorrectionLevel(ErrorCorrectionLevel.M);
To add a logo or other image to the center of the QR code, you can use the ZXing library's MergeOverlay class. Here's an example of how to do this:

    BufferedImage logo = ImageIO.read(new File("logo.png"));
    MergeOverlay mergeOverlay = new MergeOverlay();
    mergeOverlay.merge(image, logo, BufferedImage.TYPE_INT_ARGB);

This will add the image in the file "logo.png" to the center of the QR code image. You will need to add the following dependency to your pom.xml file to use the MergeOverlay class:

    <dependency>
        <groupId>com.google.zxing</groupId>
        <artifactId>javase</artifactId>
        <version>3.4.0</version>    
    </dependency>


I hope this helps! Let me know if you have any questions.