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遇到MapStruct后，再也不手写PO，DTO，VO对象之间的转换了
2022-08-04 20:20:00 【51CTO】
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
>
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对象互转
@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);
}
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- 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);
}
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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);
}
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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);
}
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多个对象映射一个对象
我们用SchoolPO和StudentPO来映射SchoolStudentVO
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);
}
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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
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();
}
}
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测试类如下
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;
}
}
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参考博客
[0]http://www.tianshouzhi.com/api/tutorials/mapstruct
[1]https://www.jianshu.com/p/3f20ca1a93b0
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