Why Not to Use Spring BeanUtils for Object Copying and How MapperStruct Improves Performance

In Java business development, copying properties between BO, PO, DTO objects often uses Spring's BeanUtils.copyProperties , but it has several drawbacks.

Inconsistent property types cause copy failure : e.g., Long vs String leads to null values.

Primitive vs wrapper mismatch : Boolean fields with is -prefixed getters may fail.

Null values overwrite existing data : copying a DTO with null fields overwrites non‑null fields in the target.

Reflection‑based implementation is slow .

Incorrect imports can cause runtime errors .

Note: If a boolean property uses both primitive and wrapper types and its name starts with is , BeanUtils may fail to copy it.

MapperStruct addresses these issues. It generates type‑safe, pre‑compiled mapping code, eliminating reflection overhead and providing much higher performance than BeanUtils.

Example of generated mapper implementation (simplified):

@Generated(value = "org.mapstruct.ap.MappingProcessor", date = "2024-02-07T00:50:05+0800", comments = "version: 1.4.2.Final, compiler: javac, environment: Java 1.8.0_211 (Oracle Corporation)")
public class XXXDTOConverterImpl implements XXXDTOConverter {
    @Override
    public XXXBO convertDtoToBo(XXXDTO xxxDTO) {
        if (xxxDTO == null) {
            return null;
        }
        XXXBO xxxBO = new XXXBO();
        xxxBO.setId(xxxDTO.getId());
        xxxBO.setLabelName(xxxDTO.getLabelName());
        xxxBO.setSortNum(xxxDTO.getSortNum());
        xxxBO.setCategoryId(xxxDTO.getCategoryId());
        return xxxBO;
    }
}

To use MapperStruct, add Maven dependencies:

<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct</artifactId>
    <version>1.4.2.Final</version>
</dependency>
<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct-processor</artifactId>
    <version>1.4.2.Final</version>
</dependency>

Define DTO and BO classes, then create a mapper interface:

@Mapper
public interface SubjectLabelDTOConverter {
    SubjectLabelDTOConverter INSTANCE = Mappers.getMapper(SubjectLabelDTOConverter.class);
    SubjectLabelBO convertDtoToBo(SubjectLabelDTO subjectLabelDTO);
}

Usage example:

public Result
add(SubjectLabelDTO subjectLabelDTO) {
    SubjectLabelBO subjectLabelBO = SubjectLabelDTOConverter.INSTANCE.convertDtoToBo(subjectLabelDTO);
    // ...
}

Note: MapperStruct also performs shallow copy; deep copy requires additional converters. When used together with Lombok, ensure Lombok dependency is declared after MapStruct to avoid null‑value issues.