OpenHTMLtoPDF Java PDF Generator

📘 Overview

OpenHTMLtoPDF is a modern, Java-based library for rendering well-structured HTML and CSS content into PDF documents. It is a more actively maintained successor to the Flying Saucer project and integrates well with any JVM-based application.

Use cases include:

• Generating reports (invoices, receipts, certificates)
• Exporting styled HTML content to PDF
• Automating document generation from templates

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🏗️ Project Structure

├── sample-pdfs/                    # Original PDF files for reference
│   ├── Sample Account Statements Report.pdf
│   └── Sample BNG P9 Report.pdf
├── src/
│   └── main/
│       └── java/
│           └── Main.java          # Main application entry point
│       └── resources/
│           ├── account-statements.html    # HTML template for account statements
│           └── p-nine-report.html         # HTML template for P9 report
├── out/
│   └── Sample BNG P9 Report.pdf   # Generated PDF output
└── test/                          # Test files (if any)

💻 Example: Simple PDF Generator in Java

import com.openhtmltopdf.pdfboxout.PdfRendererBuilder;

import java.io.*;
import java.nio.charset.StandardCharsets;

public class PDFGenerator {
    public static void main(String[] args) {
        try {
            // Read HTML content from resources
            String template = readResourceFile("templates/report.html");

            // Create output stream for the generated PDF
            try (OutputStream os = new FileOutputStream("kra_output.pdf")) {
                PdfRendererBuilder builder = new PdfRendererBuilder();
                builder.useFastMode();
                builder.withHtmlContent(template, null);
                builder.toStream(os);
                builder.run();
                System.out.println("PDF generated successfully.");
            }
        } catch (IOException e) {
            System.err.println("Error generating PDF: " + e.getMessage());
        }
    }

    private static String readResourceFile(String resourcePath) throws IOException {
        try (InputStream is = PDFGenerator.class.getClassLoader().getResourceAsStream(resourcePath)) {
            if (is == null) {
                throw new FileNotFoundException("Template not found: " + resourcePath);
            }
            return new String(is.readAllBytes(), StandardCharsets.UTF_8);
        }
    }
}

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📦 Maven Dependencies

Make sure to include these dependencies in your pom.xml:

<dependencies>
    <!-- Core engine: Required in all setups -->
    <dependency>
        <groupId>com.openhtmltopdf</groupId>
        <artifactId>openhtmltopdf-core</artifactId>
        <version>1.0.10</version>
    </dependency>

    <!-- PDF rendering backend using Apache PDFBox -->
    <dependency>
        <groupId>com.openhtmltopdf</groupId>
        <artifactId>openhtmltopdf-pdfbox</artifactId>
        <version>1.0.10</version>
    </dependency>

    <!-- Support for RTL languages and BiDi text -->
    <dependency>
        <groupId>com.openhtmltopdf</groupId>
        <artifactId>openhtmltopdf-rtl-support</artifactId>
        <version>1.0.10</version>
    </dependency>

    <!-- Logging via SLF4J -->
    <dependency>
        <groupId>com.openhtmltopdf</groupId>
        <artifactId>openhtmltopdf-slf4j</artifactId>
        <version>1.0.10</version>
    </dependency>

    <!-- Optional: SVG image rendering support -->
    <!-- <dependency>
        <groupId>com.openhtmltopdf</groupId>
        <artifactId>openhtmltopdf-svg-support</artifactId>
        <version>1.0.10</version>
    </dependency> -->

    <!-- Optional: MathML (math equations) rendering -->
    <dependency>
        <groupId>com.openhtmltopdf</groupId>
        <artifactId>openhtmltopdf-mathml-support</artifactId>
        <version>1.0.10</version>
    </dependency>

    <!-- Apache Commons Text utilities -->
    <dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-text</artifactId>
        <version>1.10.0</version>
    </dependency>
</dependencies>

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🧠 Key Concepts

Feature	Description
useFastMode()	Enables optimized performance for large documents.
withHtmlContent()	Accepts raw HTML as string input.
toStream(OutputStream)	Sets the destination for the final PDF.
run()	Starts the actual rendering and writing of the PDF.

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⚖️ Comparison with Other Tools

Tool	Language	HTML/CSS Support	Headless Browser	Output Quality
OpenHTMLtoPDF	Java	HTML5 + CSS2.1	❌	✅ Good
wkhtmltopdf	C++	HTML5 + CSS3	❌	✅ Great
Puppeteer	Node.js	Full (Chrome)	✅	🌟 Excellent
WeasyPrint	Python	HTML5 + CSS3	❌	✅ Good

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🧩 Tips & Best Practices

• Use valid XHTML or well-formed HTML.
• Avoid JavaScript — it is not supported.
• Use inline or internal CSS (no external file fetching).
• Define @page rules in CSS for margin control.
• Embed fonts for reliable rendering.

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🔚 Conclusion

OpenHTMLtoPDF is the ideal tool for Java developers needing precise and styled PDF output from HTML templates — without relying on external browser engines. It's fast, clean, and works well in enterprise Java environments.

Looking to extend? Try integrating Freemarker, Thymeleaf, or Handlebars for dynamic HTML template rendering before passing content to OpenHTMLtoPDF.