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介紹

在工作中，我們經常要進行各種對象之間的轉換。

PO：persistent object 持久對象，對應數據庫中的一條記錄
VO：view object 表現層對象，最終返回給前端的對象
DTO：data transfer object數據傳輸對象，如dubbo服務之間傳輸的對象

如果這些對象的屬性名相同還好，可以用如下工具類賦值

Spring BeanUtils Cglib BeanCopier 避免使用Apache BeanUtils，性能較差

如果屬性名不同呢？如果是將多個PO對象合并成一個VO對象呢？好在有MapStruct神器，可以幫助我們快速轉換

在pom文件中加入如下依賴即可

<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>

對象互轉

@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); }

新建一個Mapper接口，上面加上@Mapper注解

新建一個成員變量INSTANCE

用@Mapping注解指定映射關系，名字相同的就不用再指定了，會自動映射

測試效果如下，名字不同且沒有指定映射關系的會被設置為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互轉

@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類型互轉的映射規則會用單個對象的映射規則，看測試效果

@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); }

多個對象映射一個對象

我們用SchoolPO和StudentPO來映射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); }

測試例子如下

@Test public?void?mergeVo()?{SchoolPO?schoolPO?=?SchoolPO.builder().name("學校名字").build();StudentPO?studentPO?=?StudentPO.builder().name("學生名字").build();SchoolStudentVO?schoolStudentVO?=?StudentMapper.INSTANCE.mergeVo(schoolPO,?studentPO);//?SchoolStudentVO(schoolName=學校名字,?studentName=學生名字)System.out.println(schoolStudentVO); }

當然還有其他的騷操作，這里就簡單介紹一些比較實用的技巧，有興趣的可以看官方的example

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

實現原理

MapStruct幫你對接口生成了一個實現類，下面就是生成的實現類，從class文件夾中可以看到

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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總結

以上是生活随笔為你收集整理的遇到MapStruct后，再也不手写PO，DTO，VO对象之间的转换了的全部內容，希望文章能夠幫你解決所遇到的問題。

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