Barcodes with iText, ZXing & Okapi

<properties>
  <maven.compiler.release>21</maven.compiler.release>
  <itext.version>9.8.0</itext.version>
</properties>

<dependencies>
  <!-- iText Core: kernel, layout, barcodes, ... (AGPLv3 or commercial) -->
  <dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itext-core</artifactId>
    <version>${itext.version}</version>
    <type>pom</type>
  </dependency>
  <!-- ZXing encoder and readers (Apache-2.0) -->
  <dependency>
    <groupId>com.google.zxing</groupId>
    <artifactId>core</artifactId>
    <version>3.5.4</version>
  </dependency>
  <!-- Okapi Barcode (Apache-2.0) -->
  <dependency>
    <groupId>uk.org.okapibarcode</groupId>
    <artifactId>okapibarcode</artifactId>
    <version>0.5.6</version>
  </dependency>
  <!-- only for the round-trip test at the end of the page -->
  <dependency>
    <groupId>com.google.zxing</groupId>
    <artifactId>javase</artifactId>
    <version>3.5.4</version>
    <scope>test</scope>
  </dependency>
  <dependency>
    <groupId>org.apache.pdfbox</groupId>
    <artifactId>pdfbox</artifactId>
    <version>3.0.8</version>
    <scope>test</scope>
  </dependency>
</dependencies>

package demo;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.EncodeHintType;
import com.google.zxing.MultiFormatWriter;
import com.google.zxing.WriterException;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.datamatrix.encoder.SymbolShapeHint;
import com.google.zxing.qrcode.QRCodeWriter;
import com.google.zxing.qrcode.decoder.ErrorCorrectionLevel;
import com.itextpdf.kernel.colors.ColorConstants;
import com.itextpdf.kernel.geom.PageSize;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.kernel.pdf.canvas.PdfCanvas;

import java.io.IOException;
import java.util.Map;
import java.util.Locale;

public class Zxing {

    /** Encodes a QR code with exactly one BitMatrix cell per module; the quiet zone is part of the matrix. */
    static BitMatrix qrMatrix(String content, ErrorCorrectionLevel level) throws WriterException {
        Map<EncodeHintType, Object> hints = Map.of(
                EncodeHintType.ERROR_CORRECTION, level,
                EncodeHintType.CHARACTER_SET, "UTF-8",
                EncodeHintType.MARGIN, 4);
        return new QRCodeWriter().encode(content, BarcodeFormat.QR_CODE, 1, 1, hints);
    }

    /** Draws dark modules as vector rectangles, merging horizontal runs. Origin is the lower-left corner. */
    static void draw(PdfCanvas canvas, BitMatrix m, float x, float y, float moduleW, float moduleH) {
        canvas.saveState().setFillColor(ColorConstants.BLACK);
        for (int row = 0; row < m.getHeight(); row++) {
            int col = 0;
            while (col < m.getWidth()) {
                if (!m.get(col, row)) { col++; continue; }
                int start = col;
                while (col < m.getWidth() && m.get(col, row)) col++;
                canvas.rectangle(x + start * moduleW,
                        y + (m.getHeight() - 1 - row) * moduleH,
                        (col - start) * moduleW, moduleH);
            }
        }
        canvas.fill().restoreState();
    }

    /** The same matrix as an SVG document: one path, one "M x y h w v 1 h -w z" per run. */
    static String toSvg(BitMatrix m) {
        StringBuilder path = new StringBuilder();
        for (int row = 0; row < m.getHeight(); row++) {
            int col = 0;
            while (col < m.getWidth()) {
                if (!m.get(col, row)) { col++; continue; }
                int start = col;
                while (col < m.getWidth() && m.get(col, row)) col++;
                path.append(String.format(Locale.ROOT, "M%d %dh%dv1h-%dz", start, row, col - start, col - start));
            }
        }
        return "<svg xmlns=\"http://www.w3.org/2000/svg\" viewBox=\"0 0 " + m.getWidth() + " " + m.getHeight()
                + "\" shape-rendering=\"crispEdges\"><rect width=\"100%\" height=\"100%\" fill=\"#fff\"/>"
                + "<path d=\"" + path + "\" fill=\"#000\"/></svg>";
    }

    public static void main(String[] args) throws IOException, WriterException {
        BitMatrix qr = qrMatrix("https://example.com/invoices/BKS-2026-000123", ErrorCorrectionLevel.M);
        // One row of Code 128 (height 1 asks for one row); bars are stretched to 40 points when drawn.
        BitMatrix c128 = new MultiFormatWriter().encode("BKS-2026-000123", BarcodeFormat.CODE_128, 1, 1);
        BitMatrix dm = new MultiFormatWriter().encode("(01)09506000134352", BarcodeFormat.DATA_MATRIX, 1, 1,
                Map.of(EncodeHintType.DATA_MATRIX_SHAPE, SymbolShapeHint.FORCE_SQUARE));
        try (PdfDocument pdf = new PdfDocument(new PdfWriter("zxing.pdf"))) {
            PdfCanvas canvas = new PdfCanvas(pdf.addNewPage(PageSize.A5));
            draw(canvas, qr, 40, 300, 2.5f, 2.5f);
            draw(canvas, c128, 40, 220, 0.8f, 40f);
            draw(canvas, dm, 40, 140, 3f, 3f);
        }
        java.nio.file.Files.writeString(java.nio.file.Path.of("zxing-qr.svg"), toSvg(qr));
        System.out.println("qr " + qr.getWidth() + "x" + qr.getHeight() + ", c128 " + c128.getWidth() + "x" + c128.getHeight()
                + ", dm " + dm.getWidth() + "x" + dm.getHeight());
    }
}

package demo;

import com.itextpdf.kernel.colors.ColorConstants;
import com.itextpdf.kernel.geom.PageSize;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.kernel.pdf.canvas.PdfCanvas;
import uk.org.okapibarcode.backend.Code128;
import uk.org.okapibarcode.backend.DataMatrix;
import uk.org.okapibarcode.backend.Symbol;
import uk.org.okapibarcode.graphics.Rectangle;

import java.io.IOException;

public class Okapi {

    /** Okapi computes the geometry in its own units (top-left origin); we paint it as PDF rectangles. */
    static void draw(PdfCanvas canvas, Symbol symbol, float x, float yTop, float scale) {
        canvas.saveState().setFillColor(ColorConstants.BLACK);
        for (Rectangle r : symbol.getRectangles()) {
            canvas.rectangle(x + r.x * scale, yTop - (r.y + r.height) * scale, r.width * scale, r.height * scale);
        }
        canvas.fill().restoreState();
    }

    public static void main(String[] args) throws IOException {
        Code128 gs1 = new Code128();
        gs1.setDataType(Symbol.DataType.GS1);
        gs1.setContent("[01]09506000134352[17]271231[10]LOT42");   // GS1 AIs in square brackets

        DataMatrix dm = new DataMatrix();
        dm.setDataType(Symbol.DataType.GS1);
        dm.setContent("[01]09506000134352[10]LOT42");
        try (PdfDocument pdf = new PdfDocument(new PdfWriter("okapi.pdf"))) {
            PdfCanvas canvas = new PdfCanvas(pdf.addNewPage(PageSize.A5));
            draw(canvas, gs1, 40, 380, 1f);
            draw(canvas, dm, 40, 300, 3f);
        }
        System.out.println("gs1 " + gs1.getWidth() + "x" + gs1.getHeight() + " rects=" + gs1.getRectangles().size()
                + " dm " + dm.getWidth() + "x" + dm.getHeight());
    }
}

package demo;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.WriterException;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.qrcode.QRCodeWriter;
import com.itextpdf.html2pdf.HtmlConverter;

import java.io.FileOutputStream;
import java.io.IOException;

public class HtmlBarcodes {
    public static void main(String[] args) throws IOException, WriterException {
        BitMatrix qr = Zxing.qrMatrix("https://example.com/invoices/BKS-2026-000123",
                com.google.zxing.qrcode.decoder.ErrorCorrectionLevel.M);
        String svg = Zxing.toSvg(qr);
        String html = """
                <html><head><style>
                  @page { size: A5; margin: 20mm; }
                  .qr { width: 30mm; height: 30mm; }
                </style></head><body>
                  <h1>Invoice BKS-2026-000123</h1>
                  <div class="qr">%s</div>
                  <p><img class="qr" alt="Invoice QR code" src="data:image/svg+xml;base64,%s"/></p>
                </body></html>
                """.formatted(svg, java.util.Base64.getEncoder().encodeToString(svg.getBytes(java.nio.charset.StandardCharsets.UTF_8)));
        try (FileOutputStream out = new FileOutputStream("html-qr.pdf")) {
            HtmlConverter.convertToPdf(html, out);
        }
    }
}

package demo;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.BinaryBitmap;
import com.google.zxing.DecodeHintType;
import com.google.zxing.MultiFormatReader;
import com.google.zxing.NotFoundException;
import com.google.zxing.client.j2se.BufferedImageLuminanceSource;
import com.google.zxing.common.HybridBinarizer;
import org.apache.pdfbox.Loader;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.rendering.PDFRenderer;

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.nio.file.Path;
import java.util.List;
import java.util.Map;

/** Renders page 1 of a PDF that holds ONE barcode and decodes it again with ZXing. */
public class RoundTrip {

    static String decode(Path pdf, BarcodeFormat format) throws IOException, NotFoundException {
        try (PDDocument document = Loader.loadPDF(pdf.toFile())) {
            BufferedImage page = new PDFRenderer(document).renderImageWithDPI(0, 300);
            BufferedImage symbol = cropToDarkPixels(page, 60);
            var bitmap = new BinaryBitmap(new HybridBinarizer(new BufferedImageLuminanceSource(symbol)));
            return new MultiFormatReader().decode(bitmap, Map.of(
                    DecodeHintType.POSSIBLE_FORMATS, List.of(format),
                    DecodeHintType.TRY_HARDER, Boolean.TRUE)).getText();
        }
    }

    /** Cuts the dark pixels out and puts them on a white canvas with a wide quiet zone. */
    static BufferedImage cropToDarkPixels(BufferedImage page, int pad) {
        int minX = page.getWidth(), minY = page.getHeight(), maxX = 0, maxY = 0;
        for (int y = 0; y < page.getHeight(); y++) {
            for (int x = 0; x < page.getWidth(); x++) {
                if ((page.getRGB(x, y) & 0xFF) < 128) {
                    minX = Math.min(minX, x); maxX = Math.max(maxX, x);
                    minY = Math.min(minY, y); maxY = Math.max(maxY, y);
                }
            }
        }
        int w = maxX - minX + 1, h = maxY - minY + 1;
        BufferedImage out = new BufferedImage(w + 2 * pad, h + 2 * pad, BufferedImage.TYPE_INT_RGB);
        var g = out.createGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, out.getWidth(), out.getHeight());
        g.drawImage(page.getSubimage(minX, minY, w, h), pad, pad, null);
        g.dispose();
        return out;
    }

    public static void main(String[] args) throws Exception {
        // args: <format> <file.pdf>, for example QR_CODE zxing-qr.pdf
        System.out.println(decode(Path.of(args[1]), BarcodeFormat.valueOf(args[0])));
    }
}