invoice4j

invoice4j is a modular, open-source Java library for creating, reading, validating, and converting electronic invoices.

The project provides support for multiple e-invoicing standards, including ZUGFeRD, Factur-X, XRechnung, and PEPPOL BIS.

Status: Early development

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Features

• EN 16931 compliant domain model
• ZUGFeRD / Factur-X support
• XRechnung support
• Built-in invoice calculation engine
• XML validation
• Pure Java, no external services

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Supported Standards

• UN/CEFACT CII
• ZUGFeRD
• XRechnung
• UBL (planned)
• PEPPOL (planned)

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Invoice Calculation Engine

invoice4j contains a built-in calculation engine that automatically derives invoice totals according to EN 16931.

Features

• Calculates invoice line totals (BT-131)
• Supports fixed and percentage discounts
• Supports line and document level allowances/charges
• Calculates VAT breakdowns (BG-23)
• Calculates invoice monetary summation (BG-22)
• Centralized monetary arithmetic and rounding
• Validates calculation consistency

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Installation

Requirements

• Java 23 or later

<dependency>
<groupId>io.github.jcodeforge</groupId>
<artifactId>invoice4j-zugferd</artifactId>
<version>0.4.0</version>
</dependency>
<dependency>
<groupId>io.github.jcodeforge</groupId>
<artifactId>invoice4j-xr</artifactId>
<version>0.4.0</version>
</dependency>

Only add the module(s) you need. Both modules automatically include the shared invoice4j-base dependency.

Gradle (Kotlin DSL)

implementation("io.github.jcodeforge:invoice4j-zugferd:0.4.0")
implementation("io.github.jcodeforge:invoice4j-xr:0.4.0")

Gradle (Groovy)

implementation 'io.github.jcodeforge:invoice4j-zugferd:0.4.0'
implementation 'io.github.jcodeforge:invoice4j-xr:0.4.0'

invoice4j-zugferd supports ZUGFeRD and Factur-X documents. invoice4j-xr supports XRechnung. Both modules automatically include the shared core library.

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Quick Start

Complete runnable examples are available here:

invoice4j-base/src/main/java/io/github/jcodeforge/invoice4jbase/examples/QuickStart.java
invoice4j-zugferd/src/main/java/io/github/jcodeforge/invoice4jzugferd/examples/QuickStart.java

Run the example to see how to create an invoice and calculate its totals using the InvoiceCalculator.

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Examples

// Create and calculate an invoiceInvoiceinvoice = newInvoiceCalculator().calculate(TestInvoiceFactory.createMinimalInvoice());
// Create a ZUGFeRD PDFFileinputPdf = newFile("invoice.pdf");
FileoutputPdf = newFile("zugferd-invoice.pdf");
ZugferdPdfWriter.builder()
.invoice(invoice)
.profile(ZugferdProfile.EN16931)
.prettyPrint(true)
.build()
.write(inputPdf, outputPdf);
System.out.println("ZUGFeRD invoice written to: " + outputPdf);
// Read the ZUGFeRD PDF backInvoiceparsedInvoice = ZugferdPdfReader.builder()
.build()
.read(outputPdf);
System.out.println("Invoice number: " + parsedInvoice.getInvoiceNumber());
System.out.println("Seller: " + parsedInvoice.getSeller().getName());
System.out.println("Buyer: " + parsedInvoice.getBuyer().getName());
System.out.println(
"Payable amount: "
+ parsedInvoice.getMonetarySummation()
.getPayableAmount()
.getAmount()
+ " "
+ parsedInvoice.getCurrency()
);

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Running Tests

Clone the repository and execute:

mvn test

To run the complete verification including integration tests:

mvn verify

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Roadmap

Version	Milestone	Status
v0.1.0	Core Model - Invoice calculation engine	Finished
v0.2.0	CII XML	Finished
v0.3.0	ZUGFeRD	Finished
v0.4.0	XRechnung CII	Finished
v0.5.0	XRechnung UBL	In Progress
v1.0.0	Public Release	Planned
v1.1.0	PEPPOL Support	Planned
v1.2.0	Additional European e-Invoice Formats	Planned
v1.3.0	Streaming APIs	Planned
v1.4.0	Digital Signatures (XAdES/PAdES)	Planned

See the GitHub Milestones for the detailed implementation plan and progress.

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Contributing

Contributions, bug reports, feature requests, and discussions are welcome.

If you would like to contribute, please open an issue.

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License

This project is licensed under the Apache License 2.0. See the LICENSE file for details.

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Support

If invoice4j is useful to you, consider supporting its development.

Development of invoice4j requires time for implementing new features, improving documentation, maintaining standards compatibility, and providing support.

PayPal:https://paypal.me/juniorscholle

Early Development Notice

invoice4j is currently in an early development stage.

The project is published at this stage to gather feedback from developers and users working with electronic invoices such as ZUGFeRD and XRechnung.

The goal is to find out whether invoice4j solves real-world problems and whether the architecture, API design, and supported standards meet the needs of the community.

At this stage:

• The API may still change.
• Some features are not implemented yet.
• Documentation is actively being improved.
• Production usage is not recommended until a stable release is available

Feedback is highly appreciated:

• Feature requests
• Missing invoice fields or standards
• API design suggestions
• Real-world use cases
• Bug reports

If you work with electronic invoices and have requirements or suggestions, please open an issue or start a discussion.

Thank you for helping shape invoice4j.

Articles

• Invoice4j: Building ZUGFeRD and XRechnung Invoices in Java