如何在单元测试中使用包含子映射器的MapStruct

问题场景 #

你定义了包含子映射器的MapStruct接口：

@Mapper(componentModel = "spring", uses = SpouseDetailMapper.class)
public interface StudentDetailMapper {
    StudentDetailMapper INSTANCE = Mappers.getMapper(StudentDetailMapper.class);
    StudentDetailDTO toDTO(StudentDetail studentDetail);
    @InheritInverseConfiguration
    StudentDetail fromDTO(StudentDetailDTO studentDetailDTO);
}

编写StudentDetailService单元测试时，使用Mockito的@Spy处理映射器，却因子映射器未注入抛出空指针：

java.lang.NullPointerException: Cannot invoke "com.ex.project.mappers.SpouseDetailMapper.toDTO(com.ex.project.model.SpouseDetail)" because "this.spouseDetailMapper" is null

测试代码如下：

@ExtendWith(MockitoExtension.class)
class StudentDetailServiceTest {
    @Mock
    private StudentDetailRepository studentDetailRepository;

// ???
//    @InjectMocks
//    private SpouseDetailMapper spouseDetailMapper = Mappers.getMapper(SpouseDetailMapper.class);

    @Spy
    private StudentDetailMapper studentDetailMapper = Mappers.getMapper(StudentDetailMapper.class);
    @InjectMocks
    private StudentDetailService studentDetailService;

    @Test
    void getStudentDetail() {
        when(studentDetailRepository.findByStudentStudentID(anyString())).thenReturn(Optional.of(studentDetail));
//      when(spouseDetailMapper.toDTO(spouseDetail)).thenReturn(spouseDetailDTO);
        when(studentDetailMapper.toDTO(studentDetail)).thenReturn(studentDetailDTO);

        StudentDetailDTO result = studentDetailService.getStudentDetail(studentWithDetailID);

        assertThat(studentDetailDTO).isEqualTo(result);
    }

}

解决方案 #

方案1：手动注入子映射器到父映射器 #

通过Mappers.getMapper()获取的映射器实例，MapStruct不会自动注入依赖的子映射器，需手动设置：

@ExtendWith(MockitoExtension.class)
class StudentDetailServiceTest {
    @Mock
    private StudentDetailRepository studentDetailRepository;

    @Spy
    private SpouseDetailMapper spouseDetailMapper = Mappers.getMapper(SpouseDetailMapper.class);

    @Spy
    private StudentDetailMapper studentDetailMapper = Mappers.getMapper(StudentDetailMapper.class);

    @InjectMocks
    private StudentDetailService studentDetailService;

    @BeforeEach
    void setUp() {
        // 强制转换为MapStruct自动生成的实现类，注入子映射器
        ((StudentDetailMapperImpl) studentDetailMapper).setSpouseDetailMapper(spouseDetailMapper);
    }

    @Test
    void getStudentDetail() {
        when(studentDetailRepository.findByStudentStudentID(anyString())).thenReturn(Optional.of(studentDetail));
        // 如需mock子映射器逻辑，可添加以下代码
        // when(spouseDetailMapper.toDTO(spouseDetail)).thenReturn(spouseDetailDTO);

        StudentDetailDTO result = studentDetailService.getStudentDetail(studentWithDetailID);

        assertThat(studentDetailDTO).isEqualTo(result);
    }
}

注：StudentDetailMapperImpl是MapStruct编译后自动生成的实现类，需确保项目已完成编译。

方案2：借助Spring测试上下文加载映射器 #

因为你的Mapper设置了componentModel = "spring"，可以直接用Spring测试注解自动处理依赖注入：

@SpringBootTest
@ExtendWith(MockitoExtension.class)
class StudentDetailServiceTest {
    @Mock
    private StudentDetailRepository studentDetailRepository;

    @Autowired
    private StudentDetailMapper studentDetailMapper;

    @InjectMocks
    private StudentDetailService studentDetailService;

    @Test
    void getStudentDetail() {
        when(studentDetailRepository.findByStudentStudentID(anyString())).thenReturn(Optional.of(studentDetail));

        StudentDetailDTO result = studentDetailService.getStudentDetail(studentWithDetailID);

        assertThat(studentDetailDTO).isEqualTo(result);
    }
}

如果需要mock子映射器的行为，可将子映射器的@Autowired替换为@MockBean。

方案3：直接mock父映射器的完整行为 #

若只需测试Service业务逻辑，无需验证映射规则，可直接mock父映射器的方法，跳过子映射器的调用：

@ExtendWith(MockitoExtension.class)
class StudentDetailServiceTest {
    @Mock
    private StudentDetailRepository studentDetailRepository;

    @Mock
    private StudentDetailMapper studentDetailMapper;

    @InjectMocks
    private StudentDetailService studentDetailService;

    @Test
    void getStudentDetail() {
        when(studentDetailRepository.findByStudentStudentID(anyString())).thenReturn(Optional.of(studentDetail));
        when(studentDetailMapper.toDTO(studentDetail)).thenReturn(studentDetailDTO);

        StudentDetailDTO result = studentDetailService.getStudentDetail(studentWithDetailID);

        assertThat(studentDetailDTO).isEqualTo(result);
    }
}

内容的提问来源于stack exchange，提问作者vunhatchuong