遇到MapStruct后，再也不手写PO，DTO，VO对象之间的转换了！

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;         }     } }