Part of https://github.com/Payment-Components/demo-sepa#more-features-are-included-in-the-paid-version-like

SepaTestPacs008AutoReplyPacs004.java

import gr.datamation.sepa.core.messages.common.MsgReplyInfo;
import gr.datamation.sepa.core.messages.common.ReasonCode;
import gr.datamation.sepa.core.messages.eba.pacs.FIToFICustomerCreditTransfer;
import gr.datamation.sepa.core.messages.eba.pacs.PaymentReturn;

import java.util.Calendar;
import java.util.Date;
import java.util.Vector;

public class SepaTestPacs008AutoReplyPacs004 {

    public static void main(String... args) {
        execute();
    }

    public static void execute() {
        //You have to initiate the messageObject object using the suitable constructor.
        //In order to parse and validate a pacs.008 you need to use FIToFICustomerCreditTransfer
        //FIToFICustomerCreditTransfer > matches the xml element <FIToFICstmrCdtTrf>
        FIToFICustomerCreditTransfer pacs008message = new FIToFICustomerCreditTransfer();

        try {
            //Use parseAndValidateString() to fill the messageObject the content of the messageObject and validate it
            //validation fills the messageObject variable errors object with any issue found during validation
            pacs008message.parseAndValidateString(validPacs008String);

            if (pacs008message.hasValidationErrors()) {
                pacs008message.printValidationErrors();
            } else {
                System.out.println(pacs008message.toString());
            }

            System.out.println("-----------------------------\n");

            //Initialize a payment return (pacs.004) and set basic information
            PaymentReturn pacs004message = new PaymentReturn();
            //message id is commonly auto-generated by each system
            pacs004message.setElement("/GrpHdr/MsgId", "OURMESSAGEID");
            //The settlement date for our return
            pacs004message.setElement("/GrpHdr/IntrBkSttlmDt", Calendar.getInstance());
            //Select settlement method (in most cases this is set to CLRG...)
            pacs004message.setElement("/GrpHdr/SttlmInf/SttlmMtd", "CLRG");
            //and Clearing system is set to ST2
            pacs004message.setElement("/GrpHdr/SttlmInf/ClrSys/Prtry", "ST2");

            //Construct the message reply information
            //Here we are returning a message with reason code AC01 and with no charges
            //Charges have effect only for reason code FOCR (acceptance of Request for Recall)
            Vector<MsgReplyInfo> msgReplyInfo = new Vector<MsgReplyInfo>();
            ReasonCode rc = new ReasonCode(ReasonCode.CD, "AC01", null, null);

            //The message reply info has the transaction Id of the payment we want to return, the reason code info, a return Id we generate,
            //an instruction id and the settlement date of the payment that we return
            MsgReplyInfo mri = new MsgReplyInfo("TXID", rc, MsgReplyInfo.MSGID_BASED, "RETURNID", "", new Date());
            msgReplyInfo.add(mri);
            pacs004message = (PaymentReturn) pacs008message.autoReply(pacs004message, msgReplyInfo);


            if (pacs004message.hasValidationErrors()) {
                pacs004message.printValidationErrors();
            } else {
                System.out.println(pacs004message.toString());
            }

        } catch (Exception e) {
            e.printStackTrace();
            System.err.println(e.getMessage());
        }

    }

    private static final String validPacs008String = "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>\n" +
            "<Document xmlns=\"urn:iso:std:iso:20022:tech:xsd:pacs.008.001.02\">\n" +
            "    <FIToFICstmrCdtTrf>\n" +
            "        <GrpHdr>\n" +
            "            <MsgId>MESSAGEID</MsgId>\n" +
            "            <CreDtTm>2021-01-21T12:56:04</CreDtTm>\n" +
            "            <NbOfTxs>1</NbOfTxs>\n" +
            "            <TtlIntrBkSttlmAmt Ccy=\"EUR\">20</TtlIntrBkSttlmAmt>\n" +
            "            <IntrBkSttlmDt>2021-01-21</IntrBkSttlmDt>\n" +
            "            <SttlmInf>\n" +
            "                <SttlmMtd>CLRG</SttlmMtd>\n" +
            "                <ClrSys>\n" +
            "                    <Prtry>ST2</Prtry>\n" +
            "                </ClrSys>\n" +
            "            </SttlmInf>\n" +
            "            <InstdAgt>\n" +
            "                <FinInstnId>\n" +
            "                    <BIC>MILBGRAA</BIC>\n" +
            "                </FinInstnId>\n" +
            "            </InstdAgt>\n" +
            "        </GrpHdr>\n" +
            "        <CdtTrfTxInf>\n" +
            "            <PmtId>\n" +
            "                <InstrId>INSTRUCTIONID</InstrId>\n" +
            "                <EndToEndId>NOTPROVIDED</EndToEndId>\n" +
            "                <TxId>TXID</TxId>\n" +
            "            </PmtId>\n" +
            "            <PmtTpInf>\n" +
            "                <SvcLvl>\n" +
            "                    <Cd>SEPA</Cd>\n" +
            "                </SvcLvl>\n" +
            "            </PmtTpInf>\n" +
            "            <IntrBkSttlmAmt Ccy=\"EUR\">20</IntrBkSttlmAmt>\n" +
            "            <ChrgBr>SLEV</ChrgBr>\n" +
            "            <Dbtr>\n" +
            "                <Nm>DEBTOR NAME</Nm>\n" +
            "                <Id>\n" +
            "                    <OrgId>\n" +
            "                        <BICOrBEI>AAAADEFFXXX</BICOrBEI>\n" +
            "                    </OrgId>\n" +
            "                </Id>\n" +
            "            </Dbtr>\n" +
            "            <DbtrAcct>\n" +
            "                <Id>\n" +
            "                    <IBAN>DE36500400000586060600</IBAN>\n" +
            "                </Id>\n" +
            "            </DbtrAcct>\n" +
            "            <DbtrAgt>\n" +
            "                <FinInstnId>\n" +
            "                    <BIC>COBADEFFXXX</BIC>\n" +
            "                </FinInstnId>\n" +
            "            </DbtrAgt>\n" +
            "            <CdtrAgt>\n" +
            "                <FinInstnId>\n" +
            "                    <BIC>CYDBCY2N</BIC>\n" +
            "                </FinInstnId>\n" +
            "            </CdtrAgt>\n" +
            "            <Cdtr>\n" +
            "                <Nm>CREDITOR NAME</Nm>\n" +
            "                <Id>\n" +
            "                    <OrgId>\n" +
            "                        <BICOrBEI>CYDBCY2NXXX</BICOrBEI>\n" +
            "                    </OrgId>\n" +
            "                </Id>\n" +
            "            </Cdtr>\n" +
            "            <CdtrAcct>\n" +
            "                <Id>\n" +
            "                    <IBAN>CY21003000700000007011014888</IBAN>\n" +
            "                </Id>\n" +
            "            </CdtrAcct>\n" +
            "        </CdtTrfTxInf>\n" +
            "    </FIToFICstmrCdtTrf>\n" +
            "</Document>";

}