Generating Dynamic PDF Invoices with iTextPdf in Java

Background – The author needed to replace a costly reporting tool (FineReport) with a lightweight solution for generating PDF invoices in a new project. After researching alternatives, iTextPdf was chosen for its flexibility and support for Chinese characters.

Solution Overview – The approach consists of creating two PDF parts: a static template for fixed information (buyer, seller, etc.) and a dynamic table for product details, then merging them into a single document.

1. Add iTextPdf dependencies

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13.2</version>
</dependency>

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itext-asian</artifactId>
    <version>5.2.0</version>
</dependency>

2. Design the PDF template – Use Adobe Acrobat to create a fillable form, placing text fields whose names will be used as keys when populating data with iTextPdf.

3. Java implementation

3.1 Read the template

// Read local file (for demo)
PdfReader reader = new PdfReader("C:\\Users\\User\\Desktop\\开票预览模板.pdf");
// In production you would read from a byte[] obtained from S3
PdfReader reader = new PdfReader(bytes);

3.2 Fill static fields

ByteArrayOutputStream bos1 = new ByteArrayOutputStream();
PdfStamper stamper = new PdfStamper(reader, bos1);
AcroFields form = stamper.getAcroFields();
form.setGenerateAppearances(true);
form.setField("purName", "购买方对应公司");
stamper.close();

3.3 Generate dynamic product table

Document document = new Document(reader.getPageSize(1));
PdfWriter writer = PdfWriter.getInstance(document, bos2);
document.open();
BaseFont bfChinese = BaseFont.createFont("STSongStd-Light", "UniGB-UCS2-H", false);
Font font = new Font(bfChinese, 12, Font.NORMAL, BaseColor.BLACK);
PdfPTable table = generatePdfPTable(720f, font, mapData, headInfos());
document.add(table);
document.close();
writer.close();

Helper method to build the table:

public static PdfPTable generatePdfPTable(float totalWidth, Font font, List
> data, List
meta) throws DocumentException {
    PdfPTable table = new PdfPTable(meta.size());
    table.setTotalWidth(totalWidth);
    // set column widths
    float[] widths = meta.stream().mapToFloat(HeadRowMetaInfo::getWidth).toArray();
    table.setWidths(widths);
    // header
    for (HeadRowMetaInfo h : meta) {
        table.addCell(new Phrase(h.getColName(), font));
    }
    // rows
    for (Map
row : data) {
        for (HeadRowMetaInfo h : meta) {
            Object val = row.get(h.getColKey());
            table.addCell(new Phrase(val != null ? val.toString() : "-", font));
        }
    }
    table.setLockedWidth(true);
    return table;
}

3.4 Merge the two PDFs

public static byte[] copy(List
files) throws DocumentException, IOException {
    Document document = new Document();
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    PdfCopy copy = new PdfCopy(document, bos);
    document.open();
    for (byte[] file : files) {
        PdfReader reader = new PdfReader(file);
        int n = reader.getNumberOfPages();
        for (int i = 1; i <= n; i++) {
            copy.addPage(copy.getImportedPage(reader, i));
        }
        reader.close();
    }
    document.close();
    return bos.toByteArray();
}

Finally, the two byte arrays (bos1 and bos2) are combined and written to a file or uploaded to S3.

Conclusion – By creating a fillable PDF template for static content and using iTextPdf to generate a dynamic table for product lines, developers can produce complete invoice PDFs programmatically, handling both fixed and variable data efficiently.