BAEL-8522: Specifying Default Value with MapStruct (#17767)

Author: achraftt

mapstruct/src/main/java/com/baeldung/mapper/PersonMapper.java

@@ -13,5 +13,6 @@ public interface PersonMapper {
     PersonMapper INSTANCE = Mappers.getMapper(PersonMapper.class);
 
     @Mapping(target = "id", source = "person.id", defaultExpression = "java(java.util.UUID.randomUUID().toString())")
+    @Mapping(target = "name", source = "person.name", defaultValue = "anonymous")
     PersonDTO personToPersonDTO(Person person);
 }

mapstruct/src/test/java/com/baeldung/mapper/PersonMapperUnitTest.java

@@ -1,13 +1,10 @@
 package com.baeldung.mapper;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNull;
-
-import org.junit.Test;
-
 import com.baeldung.dto.PersonDTO;
 import com.baeldung.entity.Person;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
 
 public class PersonMapperUnitTest {
 
@@ -23,4 +20,16 @@ public void givenPersonEntitytoPersonWithExpression_whenMaps_thenCorrect() {
         assertNotNull(personDto.getId());
         assertEquals(personDto.getName(), entity.getName());
     }
+
+    @Test
+    public void givenPersonEntityWithNullName_whenMaps_thenCorrect() {
+        // Given a Person entity with no name set and no ID
+        Person entity = new Person();
+        entity.setId("1"); // Explicitly setting ID to null for clarity
+
+        // When mapping to PersonDTO
+        PersonDTO personDto = PersonMapper.INSTANCE.personToPersonDTO(entity);
+        // And the name in PersonDTO should be the default value "anonymous"
+        assertEquals("anonymous", personDto.getName());
+    }
 }