FINERACT-2181: Introduce customData field for Loan and LoanTransaction business events

fineract-avro-schemas/src/main/avro/loan/v1/LoanAccountDataV1.avsc

@@ -823,6 +823,17 @@
                 "null",
                 "boolean"
             ]
+        },
+        {
+            "default": null,
+            "name": "customData",
+            "type": [
+                "null",
+                {
+                    "values": "bytes",
+                    "type": "map"
+                }
+            ]
         }
     ]
 }

fineract-avro-schemas/src/main/avro/loan/v1/LoanTransactionDataV1.avsc

@@ -244,6 +244,17 @@
                 "null",
                 "string"
             ]
+        },
+        {
+            "default": null,
+            "name": "customData",
+            "type": [
+                "null",
+                {
+                    "values": "bytes",
+                    "type": "map"
+                }
+            ]
         }
     ]
 }

fineract-core/src/main/java/org/apache/fineract/infrastructure/event/external/service/serialization/serializer/ExternalEventCustomDataSerializer.java

@@ -0,0 +1,42 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.fineract.infrastructure.event.external.service.serialization.serializer;
+
+import java.nio.ByteBuffer;
+import org.apache.fineract.infrastructure.event.business.domain.BusinessEvent;
+
+public interface ExternalEventCustomDataSerializer<T extends BusinessEvent<?>> {
+
+    /**
+     * Serializes the custom data from a business event into a byte buffer
+     *
+     * @param event
+     *            The business event containing the data to serialize
+     * @return The serialized data as a ByteBuffer
+     */
+    ByteBuffer serialize(T event);
+
+    /**
+     * Returns the key used to identify this serializer's data in the custom data map
+     *
+     * @return The key string
+     */
+    String key();
+
+}

fineract-provider/src/main/java/org/apache/fineract/infrastructure/event/external/service/serialization/mapper/loan/LoanAccountDataMapper.java

@@ -37,6 +37,7 @@ public interface LoanAccountDataMapper {
     @Mapping(target = "settlementDate", ignore = true)
     @Mapping(target = "purchasePriceRatio", ignore = true)
     @Mapping(target = "delinquent.installmentDelinquencyBuckets", ignore = true)
+    @Mapping(target = "customData", ignore = true)
     LoanAccountDataV1 map(LoanAccountData source);
 
 }

fineract-provider/src/main/java/org/apache/fineract/infrastructure/event/external/service/serialization/mapper/loan/LoanTransactionDataMapper.java

@@ -30,5 +30,6 @@ public interface LoanTransactionDataMapper {
     // unpaidCharges are calculated and set explicitly based on if needed (only for charge-off transaction yet)
     @Mapping(target = "unpaidCharges", ignore = true)
     @Mapping(target = "externalOwnerId", ignore = true)
+    @Mapping(target = "customData", ignore = true)
     LoanTransactionDataV1 map(LoanTransactionData source);
 }

fineract-provider/src/main/java/org/apache/fineract/infrastructure/event/external/service/serialization/serializer/loan/LoanBusinessEventSerializer.java

@@ -18,8 +18,11 @@
  */
 package org.apache.fineract.infrastructure.event.external.service.serialization.serializer.loan;
 
+import java.nio.ByteBuffer;
 import java.util.Collection;
 import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
 import lombok.RequiredArgsConstructor;
 import org.apache.avro.generic.GenericContainer;
 import org.apache.commons.collections4.CollectionUtils;
@@ -30,6 +33,7 @@ import org.apache.fineract.infrastructure.event.business.domain.BusinessEvent;
 import org.apache.fineract.infrastructure.event.business.domain.loan.LoanBusinessEvent;
 import org.apache.fineract.infrastructure.event.external.service.serialization.mapper.loan.LoanAccountDataMapper;
 import org.apache.fineract.infrastructure.event.external.service.serialization.serializer.BusinessEventSerializer;
+import org.apache.fineract.infrastructure.event.external.service.serialization.serializer.ExternalEventCustomDataSerializer;
 import org.apache.fineract.portfolio.delinquency.service.DelinquencyReadPlatformService;
 import org.apache.fineract.portfolio.loanaccount.api.LoanApiConstants;
 import org.apache.fineract.portfolio.loanaccount.data.CollectionData;
@@ -56,6 +60,7 @@ public class LoanBusinessEventSerializer implements BusinessEventSerializer {
     private final LoanSummaryBalancesRepository loanSummaryBalancesRepository;
     @Lazy
     private final LoanSummaryProviderDelegate loanSummaryProviderDelegate;
+    private final List<ExternalEventCustomDataSerializer<LoanBusinessEvent>> externalEventCustomDataSerializers;
 
     @Override
     public <T> boolean canSerialize(BusinessEvent<T> event) {
@@ -98,8 +103,11 @@ public class LoanBusinessEventSerializer implements BusinessEventSerializer {
             data.setLoanTermVariations(activeLoanTermVariations.stream().map(LoanTermVariations::toData).toList());
         }
 
-        LoanAccountDataV1 result = mapper.map(data);
+        final LoanAccountDataV1 result = mapper.map(data);
         result.getDelinquent().setInstallmentDelinquencyBuckets(installmentsDelinquencyData);
+
+        result.setCustomData(collectCustomData(event));
+
         return result;
     }
 
@@ -107,4 +115,10 @@ public class LoanBusinessEventSerializer implements BusinessEventSerializer {
     public Class<? extends GenericContainer> getSupportedSchema() {
         return LoanAccountDataV1.class;
     }
+
+    private Map<String, ByteBuffer> collectCustomData(final LoanBusinessEvent event) {
+        return externalEventCustomDataSerializers.stream().collect(Collectors.toMap(ExternalEventCustomDataSerializer::key,
+                serializer -> serializer.serialize(event), (existing, replacement) -> replacement));
+    }
+
 }

fineract-provider/src/main/java/org/apache/fineract/infrastructure/event/external/service/serialization/serializer/loan/LoanChargeOffBusinessEventSerializer.java

@@ -19,7 +19,6 @@
 package org.apache.fineract.infrastructure.event.external.service.serialization.serializer.loan;
 
 import java.util.List;
-import org.apache.avro.generic.GenericContainer;
 import org.apache.fineract.avro.generator.ByteBufferSerializable;
 import org.apache.fineract.avro.loan.v1.LoanTransactionDataV1;
 import org.apache.fineract.infrastructure.event.business.domain.BusinessEvent;
@@ -27,6 +26,7 @@ import org.apache.fineract.infrastructure.event.business.domain.loan.transaction
 import org.apache.fineract.infrastructure.event.business.domain.loan.transaction.LoanTransactionBusinessEvent;
 import org.apache.fineract.infrastructure.event.external.service.serialization.mapper.loan.LoanTransactionDataMapper;
 import org.apache.fineract.infrastructure.event.external.service.serialization.mapper.loan.UnpaidChargeDataMapper;
+import org.apache.fineract.infrastructure.event.external.service.serialization.serializer.ExternalEventCustomDataSerializer;
 import org.apache.fineract.portfolio.loanaccount.data.UnpaidChargeData;
 import org.apache.fineract.portfolio.loanaccount.domain.LoanTransactionRepository;
 import org.apache.fineract.portfolio.loanaccount.service.LoanChargePaidByReadService;
@@ -44,8 +44,9 @@ public class LoanChargeOffBusinessEventSerializer extends LoanTransactionBusines
 
     public LoanChargeOffBusinessEventSerializer(LoanReadPlatformService loanReadPlatformService,
             LoanTransactionDataMapper loanTransactionMapper, LoanChargePaidByReadService loanChargePaidByReadService,
-            UnpaidChargeDataMapper unpaidChargeDataMapper, LoanTransactionRepository loanTransactionRepository) {
-        super(loanReadPlatformService, loanTransactionMapper, loanChargePaidByReadService);
+            UnpaidChargeDataMapper unpaidChargeDataMapper, LoanTransactionRepository loanTransactionRepository,
+            List<ExternalEventCustomDataSerializer<LoanTransactionBusinessEvent>> externalEventCustomDataSerializers) {
+        super(loanReadPlatformService, loanTransactionMapper, loanChargePaidByReadService, externalEventCustomDataSerializers);
         this.unpaidChargeDataMapper = unpaidChargeDataMapper;
         this.loanTransactionRepository = loanTransactionRepository;
     }
@@ -61,11 +62,8 @@ public class LoanChargeOffBusinessEventSerializer extends LoanTransactionBusines
         LoanTransactionBusinessEvent event = (LoanTransactionBusinessEvent) rawEvent;
         List<UnpaidChargeData> unpaidChargeDataList = loanTransactionRepository.fetchTotalUnpaidChargesForLoan(event.get().getLoan());
         transactionDataV1.setUnpaidCharges(unpaidChargeDataMapper.map(unpaidChargeDataList));
+        transactionDataV1.setCustomData(collectCustomData(event));
         return transactionDataV1;
     }
 
-    @Override
-    public Class<? extends GenericContainer> getSupportedSchema() {
-        return LoanTransactionDataV1.class;
-    }
 }

fineract-provider/src/main/java/org/apache/fineract/infrastructure/event/external/service/serialization/serializer/loan/LoanTransactionBusinessEventSerializer.java

@@ -18,6 +18,10 @@
  */
 package org.apache.fineract.infrastructure.event.external.service.serialization.serializer.loan;
 
+import java.nio.ByteBuffer;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
 import lombok.RequiredArgsConstructor;
 import org.apache.avro.generic.GenericContainer;
 import org.apache.fineract.avro.generator.ByteBufferSerializable;
@@ -26,6 +30,7 @@ import org.apache.fineract.infrastructure.event.business.domain.BusinessEvent;
 import org.apache.fineract.infrastructure.event.business.domain.loan.transaction.LoanTransactionBusinessEvent;
 import org.apache.fineract.infrastructure.event.external.service.serialization.mapper.loan.LoanTransactionDataMapper;
 import org.apache.fineract.infrastructure.event.external.service.serialization.serializer.BusinessEventSerializer;
+import org.apache.fineract.infrastructure.event.external.service.serialization.serializer.ExternalEventCustomDataSerializer;
 import org.apache.fineract.portfolio.loanaccount.data.LoanTransactionData;
 import org.apache.fineract.portfolio.loanaccount.service.LoanChargePaidByReadService;
 import org.apache.fineract.portfolio.loanaccount.service.LoanReadPlatformService;
@@ -38,6 +43,7 @@ public class LoanTransactionBusinessEventSerializer implements BusinessEventSeri
     private final LoanReadPlatformService service;
     private final LoanTransactionDataMapper loanTransactionMapper;
     private final LoanChargePaidByReadService loanChargePaidByReadService;
+    private final List<ExternalEventCustomDataSerializer<LoanTransactionBusinessEvent>> externalEventCustomDataSerializers;
 
     @Override
     public <T> boolean canSerialize(BusinessEvent<T> event) {
@@ -51,11 +57,21 @@ public class LoanTransactionBusinessEventSerializer implements BusinessEventSeri
         Long loanTransactionId = event.get().getId();
         LoanTransactionData transactionData = service.retrieveLoanTransaction(loanId, loanTransactionId);
         transactionData.setLoanChargePaidByList(loanChargePaidByReadService.fetchLoanChargesPaidByDataTransactionId(loanTransactionId));
-        return loanTransactionMapper.map(transactionData);
+
+        final LoanTransactionDataV1 result = loanTransactionMapper.map(transactionData);
+        result.setCustomData(collectCustomData(event));
+
+        return result;
     }
 
     @Override
     public Class<? extends GenericContainer> getSupportedSchema() {
         return LoanTransactionDataV1.class;
     }
+
+    protected Map<String, ByteBuffer> collectCustomData(final LoanTransactionBusinessEvent event) {
+        return externalEventCustomDataSerializers.stream().collect(Collectors.toMap(ExternalEventCustomDataSerializer::key,
+                serializer -> serializer.serialize(event), (existing, replacement) -> replacement));
+    }
+
 }

fineract-provider/src/test/java/org/apache/fineract/infrastructure/event/external/service/serialization/serializer/loan/LoanBusinessEventSerializerTest.java

@@ -0,0 +1,173 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.fineract.infrastructure.event.external.service.serialization.serializer.loan;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyLong;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import java.nio.ByteBuffer;
+import java.time.LocalDate;
+import java.time.ZoneId;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.fineract.avro.loan.v1.CollectionDataV1;
+import org.apache.fineract.avro.loan.v1.LoanAccountDataV1;
+import org.apache.fineract.infrastructure.event.business.domain.loan.LoanBusinessEvent;
+import org.apache.fineract.infrastructure.event.external.service.serialization.mapper.loan.LoanAccountDataMapper;
+import org.apache.fineract.infrastructure.event.external.service.serialization.serializer.ExternalEventCustomDataSerializer;
+import org.apache.fineract.organisation.monetary.data.CurrencyData;
+import org.apache.fineract.portfolio.delinquency.service.DelinquencyReadPlatformService;
+import org.apache.fineract.portfolio.loanaccount.data.CollectionData;
+import org.apache.fineract.portfolio.loanaccount.data.LoanAccountData;
+import org.apache.fineract.portfolio.loanaccount.data.LoanSummaryData;
+import org.apache.fineract.portfolio.loanaccount.domain.Loan;
+import org.apache.fineract.portfolio.loanaccount.domain.LoanSummary;
+import org.apache.fineract.portfolio.loanaccount.domain.LoanSummaryBalancesRepository;
+import org.apache.fineract.portfolio.loanaccount.service.LoanChargeReadPlatformService;
+import org.apache.fineract.portfolio.loanaccount.service.LoanReadPlatformService;
+import org.apache.fineract.portfolio.loanaccount.service.LoanSummaryDataProvider;
+import org.apache.fineract.portfolio.loanaccount.service.LoanSummaryProviderDelegate;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.mockito.junit.jupiter.MockitoSettings;
+import org.mockito.quality.Strictness;
+
+@MockitoSettings(strictness = Strictness.LENIENT)
+@ExtendWith(MockitoExtension.class)
+class LoanBusinessEventSerializerTest {
+
+    @Mock
+    private LoanReadPlatformService loanReadPlatformService;
+    @Mock
+    private LoanAccountDataMapper mapper;
+    @Mock
+    private LoanChargeReadPlatformService loanChargeReadPlatformService;
+    @Mock
+    private DelinquencyReadPlatformService delinquencyReadPlatformService;
+    @Mock
+    private LoanInstallmentLevelDelinquencyEventProducer installmentLevelDelinquencyEventProducer;
+    @Mock
+    private LoanSummaryBalancesRepository loanSummaryBalancesRepository;
+    @Mock
+    private LoanSummaryProviderDelegate loanSummaryProviderDelegate;
+    @Mock
+    private LoanSummaryDataProvider loanSummaryDataProvider;
+
+    private LoanBusinessEventSerializer loanBusinessEventSerializer;
+
+    @BeforeEach
+    void setUp() {
+        final List<ExternalEventCustomDataSerializer<LoanBusinessEvent>> externalEventCustomDataSerializers = List
+                .of(new ExternalEventCustomDataSerializer<>() {
+
+                    @Override
+                    public ByteBuffer serialize(final LoanBusinessEvent event) {
+                        return ByteBuffer.wrap("test_data_for_loan".getBytes(UTF_8));
+                    }
+
+                    @Override
+                    public String key() {
+                        return "test_key_1";
+                    }
+                }, new ExternalEventCustomDataSerializer<>() {
+
+                    @Override
+                    public ByteBuffer serialize(final LoanBusinessEvent event) {
+                        return ByteBuffer.wrap("test_data_for_loan_1".getBytes(UTF_8));
+                    }
+
+                    @Override
+                    public String key() {
+                        return "test_key_1";
+                    }
+                }, new ExternalEventCustomDataSerializer<>() {
+
+                    @Override
+                    public ByteBuffer serialize(final LoanBusinessEvent event) {
+                        return ByteBuffer.wrap("test_data_for_loan_2".getBytes(UTF_8));
+                    }
+
+                    @Override
+                    public String key() {
+                        return "test_key_2";
+                    }
+                });
+
+        loanBusinessEventSerializer = new LoanBusinessEventSerializer(loanReadPlatformService, mapper, loanChargeReadPlatformService,
+                delinquencyReadPlatformService, installmentLevelDelinquencyEventProducer, loanSummaryBalancesRepository,
+                loanSummaryProviderDelegate, externalEventCustomDataSerializers);
+    }
+
+    @Test
+    void testLoanCustomDataSerialization() {
+        final long loanId = 1L;
+        final Loan loan = mock(Loan.class);
+        final LoanBusinessEvent event = mock(LoanBusinessEvent.class);
+        final LoanAccountData loanAccountData = mock(LoanAccountData.class);
+        final CollectionData collectionData = mock(CollectionData.class);
+        final CurrencyData currencyData = mock(CurrencyData.class);
+        final LoanSummary loanSummary = mock(LoanSummary.class);
+        final LoanSummaryData loanSummaryData = mock(LoanSummaryData.class);
+
+        when(loan.getId()).thenReturn(loanId);
+        when(event.get()).thenReturn(loan);
+        when(loan.getActiveLoanTermVariations()).thenReturn(new ArrayList<>());
+        when(loan.getSummary()).thenReturn(loanSummary);
+
+        when(loanAccountData.getCurrency()).thenReturn(currencyData);
+        when(loanAccountData.getTransactionProcessingStrategyCode()).thenReturn("strategy-code");
+        when(loanAccountData.getSummary()).thenReturn(loanSummaryData);
+        when(loanReadPlatformService.retrieveOne(loanId)).thenReturn(loanAccountData);
+        when(loanReadPlatformService.fetchRepaymentScheduleData(loanAccountData)).thenReturn(loanAccountData);
+
+        when(delinquencyReadPlatformService.calculateLoanCollectionData(anyLong())).thenReturn(collectionData);
+        when(installmentLevelDelinquencyEventProducer.calculateInstallmentLevelDelinquencyData(any(), any())).thenReturn(new ArrayList<>());
+
+        when(loanSummaryProviderDelegate.resolveLoanSummaryDataProvider(any())).thenReturn(loanSummaryDataProvider);
+        when(loanSummaryDataProvider.withOnlyCurrencyData(any())).thenReturn(loanSummaryData);
+
+        final CollectionDataV1 collectionDataV1 = CollectionDataV1.newBuilder()
+                .setDelinquentDate(LocalDate.now(ZoneId.systemDefault()).toString()).setDelinquentDays(0)
+                .setInstallmentDelinquencyBuckets(new ArrayList<>()).build();
+
+        final LoanAccountDataV1 expectedAvroData = LoanAccountDataV1.newBuilder().setId(loanId).setCustomData(new HashMap<>())
+                .setDelinquent(collectionDataV1).build();
+
+        when(mapper.map(any(LoanAccountData.class))).thenReturn(expectedAvroData);
+
+        final LoanAccountDataV1 result = (LoanAccountDataV1) loanBusinessEventSerializer.toAvroDTO(event);
+
+        assertNotNull(result);
+        assertNotNull(result.getCustomData());
+        final Map<String, ByteBuffer> customData = result.getCustomData();
+        assertEquals("test_data_for_loan_1", new String(customData.get("test_key_1").array(), UTF_8));
+        assertEquals("test_data_for_loan_2", new String(customData.get("test_key_2").array(), UTF_8));
+    }
+
+}

fineract-provider/src/test/java/org/apache/fineract/infrastructure/event/external/service/serialization/serializer/loan/LoanTransactionBusinessEventSerializerTest.java

@@ -0,0 +1,136 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.fineract.infrastructure.event.external.service.serialization.serializer.loan;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyLong;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.fineract.avro.loan.v1.LoanTransactionDataV1;
+import org.apache.fineract.infrastructure.event.business.domain.loan.transaction.LoanTransactionBusinessEvent;
+import org.apache.fineract.infrastructure.event.external.service.serialization.mapper.loan.LoanTransactionDataMapper;
+import org.apache.fineract.infrastructure.event.external.service.serialization.serializer.ExternalEventCustomDataSerializer;
+import org.apache.fineract.portfolio.loanaccount.data.LoanTransactionData;
+import org.apache.fineract.portfolio.loanaccount.domain.Loan;
+import org.apache.fineract.portfolio.loanaccount.domain.LoanTransaction;
+import org.apache.fineract.portfolio.loanaccount.service.LoanChargePaidByReadService;
+import org.apache.fineract.portfolio.loanaccount.service.LoanReadPlatformService;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.mockito.junit.jupiter.MockitoSettings;
+import org.mockito.quality.Strictness;
+
+@MockitoSettings(strictness = Strictness.LENIENT)
+@ExtendWith(MockitoExtension.class)
+class LoanTransactionBusinessEventSerializerTest {
+
+    @Mock
+    private LoanReadPlatformService loanReadPlatformService;
+    @Mock
+    private LoanTransactionDataMapper loanTransactionMapper;
+    @Mock
+    private LoanChargePaidByReadService loanChargePaidByReadService;
+
+    private LoanTransactionBusinessEventSerializer serializer;
+
+    @BeforeEach
+    void setUp() {
+        final List<ExternalEventCustomDataSerializer<LoanTransactionBusinessEvent>> externalEventCustomDataSerializers = List
+                .of(new ExternalEventCustomDataSerializer<>() {
+
+                    @Override
+                    public ByteBuffer serialize(final LoanTransactionBusinessEvent event) {
+                        return ByteBuffer.wrap("test_data_for_loan_transaction".getBytes(UTF_8));
+                    }
+
+                    @Override
+                    public String key() {
+                        return "test_key_1";
+                    }
+                }, new ExternalEventCustomDataSerializer<>() {
+
+                    @Override
+                    public ByteBuffer serialize(final LoanTransactionBusinessEvent event) {
+                        return ByteBuffer.wrap("test_data_for_loan_transaction_1".getBytes(UTF_8));
+                    }
+
+                    @Override
+                    public String key() {
+                        return "test_key_1";
+                    }
+                }, new ExternalEventCustomDataSerializer<>() {
+
+                    @Override
+                    public ByteBuffer serialize(final LoanTransactionBusinessEvent event) {
+                        return ByteBuffer.wrap("test_data_for_loan_transaction_2".getBytes(UTF_8));
+                    }
+
+                    @Override
+                    public String key() {
+                        return "test_key_2";
+                    }
+                });
+        serializer = new LoanTransactionBusinessEventSerializer(loanReadPlatformService, loanTransactionMapper, loanChargePaidByReadService,
+                externalEventCustomDataSerializers);
+    }
+
+    @Test
+    void testTransactionCustomDataSerialization() {
+        final long loanId = 1;
+        final long transactionId = 2;
+
+        final Loan loan = mock(Loan.class);
+        final LoanTransaction loanTransaction = mock(LoanTransaction.class);
+        final LoanTransactionBusinessEvent event = mock(LoanTransactionBusinessEvent.class);
+        final LoanTransactionData transactionData = mock(LoanTransactionData.class);
+
+        when(loan.getId()).thenReturn(loanId);
+        when(loanTransaction.getId()).thenReturn(transactionId);
+        when(loanTransaction.getLoan()).thenReturn(loan);
+        when(event.get()).thenReturn(loanTransaction);
+
+        when(loanReadPlatformService.retrieveLoanTransaction(loanId, transactionId)).thenReturn(transactionData);
+        when(loanChargePaidByReadService.fetchLoanChargesPaidByDataTransactionId(anyLong())).thenReturn(new ArrayList<>());
+
+        final LoanTransactionDataV1 expectedAvroData = LoanTransactionDataV1.newBuilder().setId(transactionId).setLoanId(loanId)
+                .setCustomData(new HashMap<>()).build();
+        when(loanTransactionMapper.map(any(LoanTransactionData.class))).thenReturn(expectedAvroData);
+
+        final LoanTransactionDataV1 result = (LoanTransactionDataV1) serializer.toAvroDTO(event);
+
+        assertNotNull(result);
+        assertNotNull(result.getCustomData());
+        final Map<String, ByteBuffer> customData = result.getCustomData();
+        assertEquals("test_data_for_loan_transaction_1", new String(customData.get("test_key_1").array(), UTF_8));
+        assertEquals("test_data_for_loan_transaction_2", new String(customData.get("test_key_2").array(), UTF_8));
+    }
+
+}