遇到MapStruct后，再也不手写PO，DTO，VO对象之间的转换了

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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，这里就简单介绍一些比较实用的技巧，有兴趣的可以看官方的example

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

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 {public StudentMapperImpl() {}public StudentVO po2Vo(StudentPO studentPO) {if (studentPO == null) {return null;} else {StudentVO studentVO = new StudentVO();studentVO.setStudentAge(studentPO.getAge());studentVO.setStudentName(studentPO.getName());studentVO.setId(studentPO.getId());return studentVO;}}public List<StudentVO> poList2VoList(List<StudentPO> studentPO) {if (studentPO == null) {return null;} else {List<StudentVO> list = new ArrayList(studentPO.size());Iterator var3 = studentPO.iterator();while(var3.hasNext()) {StudentPO studentPO1 = (StudentPO)var3.next();list.add(this.po2Vo(studentPO1));}return list;}}public SchoolStudentVO mergeVo(SchoolPO schoolPO, StudentPO studentPO) {if (schoolPO == null && studentPO == null) {return null;} else {SchoolStudentVO schoolStudentVO = new SchoolStudentVO();if (schoolPO != null) {schoolStudentVO.setSchoolName(schoolPO.getName());}if (studentPO != null) {schoolStudentVO.setStudentName(studentPO.getName());}return schoolStudentVO;}}
}

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