遇到MapStruct后，再也不手写PO，DTO，VO对象之间的转换了-CFANZ编程社区

遇到MapStruct后，再也不手写PO，DTO，VO对象之间的转换了_ide

介绍

在工作中，我们经常要进行各种对象之间的转换。

PO：persistent object 持久对象，对应数据库中的一条记录
VO：view object 表现层对象，最终返回给前端的对象
DTO：data transfer object数据传输对象，如dubbo服务之间传输的对象

如果这些对象的属性名相同还好，可以用如下工具类赋值

Spring BeanUtils
Cglib BeanCopier
避免使用Apache BeanUtils，性能较差

如果属性名不同呢？如果是将多个PO对象合并成一个VO对象呢？好在有MapStruct神器，可以帮助我们快速转换

在pom文件中加入如下依赖即可

<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct-jdk8</artifactId>
    <version>1.2.0.CR1</version>
</dependency>

<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct-processor</artifactId>
    <version>1.2.0.CR1</version>
    <scope>provided</scope>
</dependency>

对象互转

@Data
@Builder
public class StudentPO {

    private Integer id;
    private String name;
    private Integer age;
    private String className;
}

@Data
public class StudentVO {

    private Integer id;
    private String studentName;
    private Integer studentAge;
    private String schoolName;
}

@Mapper
public interface StudentMapper {

    StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

    @Mappings({
            @Mapping(source = "name", target = "studentName"),
            @Mapping(source = "age", target = "studentAge")
    })
    StudentVO po2Vo(StudentPO studentPO);
}

新建一个Mapper接口，上面加上@Mapper注解
新建一个成员变量INSTANCE
用@Mapping注解指定映射关系，名字相同的就不用再指定了，会自动映射

测试效果如下，名字不同且没有指定映射关系的会被设置为null

@Test
public void studentPo2Vo() {
    StudentPO studentPO = StudentPO.builder().id(10).name("test")
            .age(24).className("教室名").build();
    StudentVO studentVO = StudentMapper.INSTANCE.po2Vo(studentPO);
    // StudentVO(id=10, studentName=test, studentAge=24, schoolName=null)
    System.out.println(studentVO);
}

List互转

@Mapper
public interface StudentMapper {

    StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

    @Mappings({
            @Mapping(source = "name", target = "studentName"),
            @Mapping(source = "age", target = "studentAge")
    })
    StudentVO po2Vo(StudentPO studentPO);

    List<StudentVO> poList2VoList(List<StudentPO> studentPO);
}

List类型互转的映射规则会用单个对象的映射规则，看测试效果

@Test
public void poList2VoList() {
    List<StudentPO> studentPOList = new ArrayList<>();
    for (int i = 1; i <= 2; i++) {
        StudentPO studentPO = StudentPO.builder().id(i).name(String.valueOf(i)).age(i).build();
        studentPOList.add(studentPO);
    }
    List<StudentVO> studentVOList = StudentMapper.INSTANCE.poList2VoList(studentPOList);
    // [StudentVO(id=1, studentName=1, studentAge=1, schoolName=null),
    // StudentVO(id=2, studentName=2, studentAge=2, schoolName=null)]
    System.out.println(studentVOList);
}

多个对象映射一个对象

我们用SchoolPO和StudentPO来映射SchoolStudentVO

@Data
@Builder
public class SchoolPO {

    private String name;
    private String location;
}

@Data
@Builder
public class StudentPO {

    private Integer id;
    private String name;
    private Integer age;
    private String className;
}

@Data
public class SchoolStudentVO {

    private String schoolName;
    private String studentName;
}

@Mapper
public interface StudentMapper {

    @Mappings({
            @Mapping(source = "schoolPO.name", target = "schoolName"),
            @Mapping(source = "studentPO.name", target = "studentName")
    })
    SchoolStudentVO mergeVo(SchoolPO schoolPO, StudentPO studentPO);
}

测试例子如下

@Test
public void mergeVo() {
    SchoolPO schoolPO = SchoolPO.builder().name("学校名字").build();
    StudentPO studentPO = StudentPO.builder().name("学生名字").build();
    SchoolStudentVO schoolStudentVO = StudentMapper.INSTANCE.mergeVo(schoolPO, studentPO);
    // SchoolStudentVO(schoolName=学校名字, studentName=学生名字)
    System.out.println(schoolStudentVO);
}

当然还有其他的骚操作，这里就简单介绍一个比较实用的技巧，有兴趣的可以看官方的example

https://github.com/mapstruct/mapstruct-examples

转换的时候指定方法

@Data
@Builder
public class PersonVO {

    private int age;
    private GenderEnum gender;
}

@Getter
@AllArgsConstructor
public enum GenderEnum {

    FEMALE(0, "女性"),
    MALE(1, "男性");

    private int value;
    private String name;

}

@Data
public class PersonPO {

    private int age;
    private int gender;
}

当我们想把PersonVO转换为PersonPO，PersonPO中的gender是一个枚举，PersonVO中的gender是一个int类型，如何把枚举转为枚举的value值呢？

在@Mapping注解中通过qualifiedByName属性指定转换的方法

@Mapper
public interface StudentMapper {

    StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

    @Mappings({
            @Mapping(source = "gender", target = "gender", qualifiedByName = "convertGender"),
    })
    PersonPO vo2Po(PersonVO personVO);

    @Named("convertGender")
    default Integer convertTargetType(GenderEnum genderEnum) {
        return genderEnum.getValue();
    }

}

测试类如下

@Test
public void specifyMethod() {
    PersonVO personVO = PersonVO.builder().age(10).gender(GenderEnum.MALE).build();
    PersonPO personPO = StudentMapper.INSTANCE.vo2Po(personVO);
    // PersonPO(age=10, gender=1)
    System.out.println(personPO);
}

实现原理

MapStruct帮你对接口生成了一个实现类，下面就是生成的实现类，从class文件夹中可以看到

public class StudentMapperImpl implements StudentMapper {

    @Override

    public StudentVO po2Vo(StudentPO studentPO) {

        if ( studentPO == null ) {

            return null;
        }

        StudentVO studentVO = new StudentVO();

        studentVO.setStudentAge( studentPO.getAge() );

        studentVO.setStudentName( studentPO.getName() );

        studentVO.setId( studentPO.getId() );

        return studentVO;
    }

    @Override

    public List<StudentVO> poList2VoList(List<StudentPO> studentPO) {

        if ( studentPO == null ) {

            return null;
        }

        List<StudentVO> list = new ArrayList<StudentVO>( studentPO.size() );

        for ( StudentPO studentPO1 : studentPO ) {

            list.add( po2Vo( studentPO1 ) );
        }

        return list;
    }

    @Override

    public SchoolStudentVO mergeVo(SchoolPO schoolPO, StudentPO studentPO) {

        if ( schoolPO == null && studentPO == null ) {

            return null;
        }

        SchoolStudentVO schoolStudentVO = new SchoolStudentVO();

        if ( schoolPO != null ) {

            schoolStudentVO.setSchoolName( schoolPO.getName() );
        }

        if ( studentPO != null ) {

            schoolStudentVO.setStudentName( studentPO.getName() );
        }

        return schoolStudentVO;
    }

    @Override

    public PersonPO vo2Po(PersonVO personVO) {

        if ( personVO == null ) {

            return null;
        }

        PersonPO personPO = new PersonPO();

        personPO.setGender( convertTargetType( personVO.getGender() ) );

        personPO.setAge( personVO.getAge() );

        return personPO;
    }
}