Generate a QR code in Java

ZXing in two artifacts

ZXing ("zebra crossing") is the JVM's standard barcode library, and it ships split in two: com.google.zxing:core holds the encoder and decoder, while com.google.zxing:javase holds the desktop I/O helpers, including MatrixToImageWriter, which you need to actually write a PNG. Forgetting javase is the classic first compile error.

<dependency><groupId>com.google.zxing</groupId><artifactId>core</artifactId><version>3.5.3</version></dependency>
<dependency><groupId>com.google.zxing</groupId><artifactId>javase</artifactId><version>3.5.3</version></dependency>

Encode, hint, write

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

Map<EncodeHintType, Object> hints = new EnumMap<>(EncodeHintType.class);
hints.put(EncodeHintType.ERROR_CORRECTION, ErrorCorrectionLevel.Q);
hints.put(EncodeHintType.MARGIN, 4);

BitMatrix matrix = new MultiFormatWriter()
    .encode("https://example.com", BarcodeFormat.QR_CODE, 512, 512, hints);
MatrixToImageWriter.writeToPath(matrix, "PNG", Path.of("qr.png"));

The hint map is where correctness lives. MARGIN is the quiet zone in modules: keep it at 4; ERROR_CORRECTION takes the four levels L, M, Q, H. For in-memory use, MatrixToImageWriter.toBufferedImage(matrix) returns a BufferedImage you can hand to ImageIO or a servlet response.

The zero-dependency route: HttpClient

Java 11's built-in java.net.http client makes the keyless API a no-dependency option: useful when you want styled output or typed payloads (WiFi, vCard, UPI) without renderer code:

String data = URLEncoder.encode("https://example.com/sale?src=poster",
    StandardCharsets.UTF_8);
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder(
    URI.create("https://useqr.app/api/v1/qr?data=" + data + "&size=1024&ec=Q")).build();
client.send(request, HttpResponse.BodyHandlers.ofFile(Path.of("qr.png")));

URLEncoder.encode is not optional: a raw & inside the payload starts a new query parameter and the encoded data is silently truncated. Add format=svg when the output is headed to print: ZXing itself has no SVG writer.

Decode-verify with the library you already have

ZXing decodes too, so a Java test can round-trip its own output:

BufferedImage img = ImageIO.read(new File("qr.png"));
LuminanceSource source = new BufferedImageLuminanceSource(img);
BinaryBitmap bitmap = new BinaryBitmap(new HybridBinarizer(source));
Result result = new MultiFormatReader().decode(bitmap);
assertEquals("https://example.com", result.getText());

For styled or logo-carrying codes generated via the API, GET /api/v1/verify runs the render-rasterise-decode loop server-side and reports scannable with issues: the reasoning is in why verify that your QR code decodes, and how ZXing's decoder compares with quirc and ZBar is in zxing vs quirc vs zbar. On Android, the idiomatic wrapper is different: see the Kotlin page.

FAQ

What is the standard Java library for QR codes?

ZXing. Use MultiFormatWriter to encode into a BitMatrix and MatrixToImageWriter, from the separate javase artifact, to write image files.

Why can't Java find MatrixToImageWriter?

It lives in com.google.zxing:javase, not core. Add the javase artifact alongside core and the import resolves.

How do I set error correction and margin in ZXing?

Pass an EnumMap of EncodeHintType entries to encode: ERROR_CORRECTION with an ErrorCorrectionLevel, and MARGIN with the quiet-zone width in modules: keep it at 4.

Can ZXing produce SVG?

No, it renders to a BitMatrix and raster images. For SVG output, call the keyless API with format=svg or render the matrix yourself.