import ch.codeblock.qrinvoice.FontFamily;
import ch.codeblock.qrinvoice.OutputFormat;
import ch.codeblock.qrinvoice.PageSize;
import ch.codeblock.qrinvoice.QrInvoicePaymentPartReceiptCreator;
import ch.codeblock.qrinvoice.model.QrInvoice;
import ch.codeblock.qrinvoice.model.builder.QrInvoiceBuilder;
import ch.codeblock.qrinvoice.model.validation.ValidationException;
import ch.codeblock.qrinvoice.model.validation.ValidationResult;
import ch.codeblock.qrinvoice.output.PaymentPartReceipt;

import java.io.FileOutputStream;
import java.util.Locale;

public class QrInvoiceBuilderTypicalExample {
    public static void main(String[] args) {
        // 1. Build the invoice object
        QrInvoice qrInvoice = buildInvoice();

        // 2. Generate the payment part as PDF
        byte[] qrBillPdf = createQrBill(qrInvoice);

        // 3. Write the PDF
        writePdf(qrBillPdf);
    }

    private static QrInvoice buildInvoice() {
        QrInvoice qrInvoice = null;

        try {
            qrInvoice = QrInvoiceBuilder
                    .create()
                    .creditorIBAN("CH44 3199 9123 0008 8901 2")
                    .paymentAmountInformation(p -> p
                            .chf(1949.75)
                    )
                    .creditor(c -> c
                            .structuredAddress()
                            .name("Robert Schneider AG")
                            .streetName("Rue du Lac")
                            .houseNumber("1268")
                            .postalCode("2501")
                            .city("Biel")
                            .country("CH")
                    )
                    .ultimateDebtor(d -> d
                            .structuredAddress()
                            .name("Pia-Maria Rutschmann-Schnyder")
                            .streetName("Grosse Marktgasse")
                            .houseNumber("28")
                            .postalCode("9400")
                            .city("Rorschach")
                            .country("CH")
                    )
                    .paymentReference(r -> r
                            .qrReference("210000000003139471430009017")
                    )
                    .additionalInformation(a -> a
                            .unstructuredMessage("Instruction of 03.04.2019") // Max. 140 characters, no linebreaks
                    )
                    .build();
        } catch (ValidationException validationException) {
            final ValidationResult validationResult = validationException.getValidationResult();

            System.out.println(validationResult.getValidationErrorSummary());
            System.exit(1);
        }

        return qrInvoice;
    }

    private static byte[] createQrBill(QrInvoice qrInvoice) {
        final PaymentPartReceipt paymentPartReceipt = QrInvoicePaymentPartReceiptCreator
                .create()
                .qrInvoice(qrInvoice)
                .outputFormat(OutputFormat.PDF)
                .pageSize(PageSize.A4) // Use DIN_LANG to generate a A6 page with the payment part only
                .fontFamily(FontFamily.LIBERATION_SANS) // or HELVETICA, ARIAL
                .locale(Locale.GERMAN) // Supported: GERMAN, FRENCH, ENGLISH, ITALIAN
                .createPaymentPartReceipt();

        // the resulting byte array contains the payment part & receipt as PDF
        return paymentPartReceipt.getData();
    }

    private static void writePdf(byte[] qrBillPdf) {
        try (FileOutputStream stream = new FileOutputStream("paymentPart.pdf")) {
            stream.write(qrBillPdf);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import ch.codeblock.qrinvoice.pdf.QrPdfMerger;

import java.io.FileOutputStream;
import java.nio.file.Files;
import java.nio.file.Paths;

public class CombinePdfs {
    public static void main(String[] args) {
        try {
            // 1. Read in invoice part
            byte[] invoice = Files.readAllBytes(Paths.get("invoice.pdf"));

            // 2. Read in payment part (Generated by QrInvoiceBuilderTypicalExample.java)
            byte[] paymentPart = Files.readAllBytes(Paths.get("paymentPart.pdf"));

            // 3. Merge files
            byte[] qrBill = QrPdfMerger.create().mergePdfs(paymentPart, invoice);

            // 4. Write merged QR bill
            FileOutputStream qrBillFile = new FileOutputStream("qrBill.pdf");
            qrBillFile.write(qrBill);
            qrBillFile.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}