遇到MapStruct后,再也不手写PO,DTO,VO对象之间的转换了!

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遇到MapStruct后,再也不手写PO,DTO,VO对象之间的转换了!

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);
}
  1. 新建一个Mapper接口,上面加上@Mapper注解

  2. 新建一个成员变量INSTANCE

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

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