Build a Java QR Code Generator with ZXing in 15 Minutes

Java QR Code Generator: Step-by-Step Guide for Beginners

QR codes are a fast, reliable way to encode URLs, contact details, and other small data in a scannable image. This guide walks you through building a simple Java QR code generator using the popular ZXing library. No prior QR experience required — follow the steps and you’ll have a reusable utility that produces PNG QR codes with configurable size, color, and error correction.

What you’ll need

• Java 11+ (or any recent Java version)
• Maven or Gradle for dependency management
• A text editor or IDE (IntelliJ, Eclipse, VS Code)
• ZXing core and JavaSE modules

Step 1 — Create a new project

Set up a basic Maven project. Example pom.xml dependencies:

xml
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<dependencies>
<dependency>
    <groupId>com.google.zxing</groupId>
    <artifactId>core</artifactId>
    <version>3.5.1</version>
  </dependency>
  <dependency>
    <groupId>com.google.zxing</groupId>
    <artifactId>javase</artifactId>
    <version>3.5.1</version>
  </dependency>
</dependencies>

(If you use Gradle, add the equivalent to build.gradle.)

Step 2 — Basic QR generator code

Create a Java class (QrGenerator.java). This example produces a PNG file from input text:

java
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import com.google.zxing.*;
import com.google.zxing.client.j2se.MatrixToImageConfig;
import com.google.zxing.client.j2se.MatrixToImageWriter;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.qrcode.decoder.ErrorCorrectionLevel;

import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.HashMap;
import java.util.Map;

public class QrGenerator {
    public static void generate(String text, int size, Path outputFile) throws Exception {
        Map<EncodeHintType, Object> hints = new HashMap<>();
        hints.put(EncodeHintType.CHARACTER_SET, “UTF-8”);
        hints.put(EncodeHintType.ERROR_CORRECTION, ErrorCorrectionLevel.M); // L, M, Q, H
        hints.put(EncodeHintType.MARGIN, 1);

        BitMatrix matrix = new MultiFormatWriter()
                .encode(text, BarcodeFormat.QR_CODE, size, size, hints);

        // Optional: customize colors (foreground, background)
        int fg = 0xFF000000; // black
        int bg = 0xFFFFFFFF; // white
        MatrixToImageConfig config = new MatrixToImageConfig(fg, bg);

        MatrixToImageWriter.writeToPath(matrix, “PNG”, outputFile, config);
    }

    public static void main(String[] args) throws Exception {
        String text = args.length > 0 ? args[0] : “https://example.com”;
        int size = 300;
        Path out = Paths.get(“qrcode.png”);
        generate(text, size, out);
        System.out.println(“QR written to “ + out.toAbsolutePath());
    }
}

Step 3 — Run and test

• Build with Maven: mvn package
• Run: java -cp target/your-jar.jar QrGenerator “https://your-site.example”
• Open the generated qrcode.png and scan with your phone.

Step 4 — Customization options

• Size: change the size parameter (e.g., 150–1000 px).
• Error correction: use ErrorCorrectionLevel.L/M/Q/H (higher = more redundancy, larger/denser QR).
• Margin: adjust EncodeHintType.MARGIN (0–4) to control white border.
• Colors: change fg/bg in MatrixToImageConfig for branding.
• Output formats: write to JPG or write image to an OutputStream for web responses.

Step 5 — Embedding in web apps

• For Java servlets or Spring Boot controllers, write the image to the HTTP response OutputStream with content-type image/png.
• Example (Spring Boot):

java
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@GetMapping(”/qrcode”)
public void qrcode(@RequestParam String text, HttpServletResponse resp) throws Exception {
    resp.setContentType(“image/png”);
    Path tmp = Files.createTempFile(“qr”, ”.png”);
    QrGenerator.generate(text, 300, tmp);
    Files.copy(tmp, resp.getOutputStream());
    Files.delete(tmp);
}

Step 6 — Error handling & security notes

• Validate input length — QR codes have capacity limits depending on charset and error correction.
• Sanitize user-provided URLs if embedding in pages.
• Avoid storing sensitive personal data in QR codes unless encrypted.

Troubleshooting

• Blurry image when scanned: increase size or error correction.
• Not encoding special characters: ensure CHARACTER_SET is UTF-8.
• Library conflicts: ensure only one ZXing version on the classpath.

Quick reference: common QR capacities (approx.)

• Numeric only: up to ~7,000 digits
• Alphanumeric: up to ~4,200 characters
• Binary (bytes): up to ~2,900 bytes Actual capacity depends on error correction and version.

This gives you a working Java QR code generator you can expand for web apps, batch generation, or custom styling.