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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】

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
       
       >
      
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对象互转

       
       @Data
       
       @Builder
       
       public 
       
       class 
       
       StudentPO {
       
       private 
       
       Integer 
       
       id;
       
       private 
       
       String 
       
       name;
       
       private 
       
       Integer 
       
       age;
       
       private 
       
       String 
       
       className;
       
}
      
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       @Data
       
       public 
       
       class 
       
       StudentVO {
       
       private 
       
       Integer 
       
       id;
       
       private 
       
       String 
       
       studentName;
       
       private 
       
       Integer 
       
       studentAge;
       
       private 
       
       String 
       
       schoolName;
       
}
      
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       @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

       
       @Data
       
       @Builder
       
       public 
       
       class 
       
       SchoolPO {
       
       private 
       
       String 
       
       name;
       
       private 
       
       String 
       
       location;
       
}
      
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       @Data
       
       @Builder
       
       public 
       
       class 
       
       StudentPO {
       
       private 
       
       Integer 
       
       id;
       
       private 
       
       String 
       
       name;
       
       private 
       
       Integer 
       
       age;
       
       private 
       
       String 
       
       className;
       
}
      
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       @Data
       
       public 
       
       class 
       
       SchoolStudentVO {
       
       private 
       
       String 
       
       schoolName;
       
       private 
       
       String 
       
       studentName;
       
}
      
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       @Mapper
       
       public 
       
       interface 
       
       StudentMapper {
       
       @Mappings({
       
       @Mapping(
       
       source 
       
       = 
       
       "schoolPO.name", 
       
       target 
       
       = 
       
       "schoolName"),
       
       @Mapping(
       
       source 
       
       = 
       
       "studentPO.name", 
       
       target 
       
       = 
       
       "studentName")
       
    })
       
       SchoolStudentVO 
       
       mergeVo(
       
       SchoolPO 
       
       schoolPO, 
       
       StudentPO 
       
       studentPO);
       
}
      
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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

       
       @Data
       
       @Builder
       
       public 
       
       class 
       
       PersonVO {
       
       private 
       
       int 
       
       age;
       
       private 
       
       GenderEnum 
       
       gender;
       
}
      
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       @Getter
       
       @AllArgsConstructor
       
       public 
       
       enum 
       
       GenderEnum {
       
       FEMALE(
       
       0, 
       
       "女性"),
       
       MALE(
       
       1, 
       
       "男性");
       
       private 
       
       int 
       
       value;
       
       private 
       
       String 
       
       name;
       
}
      
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       @Data
       
       public 
       
       class 
       
       PersonPO {
       
       private 
       
       int 
       
       age;
       
       private 
       
       int 
       
       gender;
       
}
      
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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

       
       @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);
       
}
      
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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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