老鐵們是不是經(jīng)常為寫一些實體轉(zhuǎn)換的原始代碼感到頭疼，尤其是實體字段特別多的時候。介紹一個開源項目 mapstruct ，可以輕松優(yōu)雅的進(jìn)行轉(zhuǎn)換，簡化你的代碼。當(dāng)然有的人喜歡寫get set，或者用BeanUtils 進(jìn)行復(fù)制，代碼只是工具，本文只是提供一種思路。

先貼下官網(wǎng)地址吧：https://mapstruct.org/

廢話不多說，上代碼：

pom 配置：

<properties>
<project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
<maven.compiler.source>1.8maven.compiler.source>
<maven.compiler.target>1.8maven.compiler.target>
<org.mapstruct.version>1.4.1.Finalorg.mapstruct.version>
<org.projectlombok.version>1.18.12org.projectlombok.version>
properties>

<dependencies>
<dependency>
<groupId>org.mapstructgroupId>
<artifactId>mapstructartifactId>
<version>${org.mapstruct.version}version>
dependency>


<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
<version>${org.projectlombok.version}version>
<scope>providedscope>
dependency>


<dependency>
<groupId>org.mapstructgroupId>
<artifactId>mapstruct-processorartifactId>
<version>${org.mapstruct.version}version>
<scope>providedscope>
dependency>

dependencies>

<build>
<plugins>
<plugin>
<groupId>org.apache.maven.pluginsgroupId>
<artifactId>maven-compiler-pluginartifactId>
<version>3.8.1version>
<configuration>
<source>1.8source>
<target>1.8target>
<annotationProcessorPaths>
<path>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
<version>${org.projectlombok.version}version>
path>
<path>
<groupId>org.mapstructgroupId>
<artifactId>mapstruct-processorartifactId>
<version>${org.mapstruct.version}version>
path>
annotationProcessorPaths>
configuration>
plugin>
plugins>
build>

關(guān)于lombok和mapstruct的版本兼容問題多說幾句，maven插件要使用3.6.0版本以上、lombok使用1.16.16版本以上，另外編譯的lombok mapstruct的插件不要忘了加上。否則會出現(xiàn)下面的錯誤：No property named "aaa" exists in source parameter(s). Did you mean "null"?

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這種異常就是lombok編譯異常導(dǎo)致缺少get setter方法造成的。還有就是缺少構(gòu)造函數(shù)也會拋異常。

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
publicclassStudent{

privateStringname;
privateintage;
privateGenderEnumgender;
privateDoubleheight;
privateDatebirthday;

}
publicenumGenderEnum{
Male("1","男"),
Female("0","女");

privateStringcode;
privateStringname;

publicStringgetCode(){
returnthis.code;
}

publicStringgetName(){
returnthis.name;
}

GenderEnum(Stringcode,Stringname){
this.code=code;
this.name=name;
}
}
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
publicclassStudentVO{
privateStringname;
privateintage;
privateStringgender;
privateDoubleheight;
privateStringbirthday;
}
@Mapper
publicinterfaceStudentMapper{

StudentMapperINSTANCE=Mappers.getMapper(StudentMapper.class);

@Mapping(source="gender.name",target="gender")
@Mapping(source="birthday",target="birthday",dateFormat="yyyy-MM-ddHHss")
StudentVOstudent2StudentVO(Studentstudent);

}

實體類是開發(fā)過程少不了的，就算是用工具生成肯定也是要有的，需要手寫的部分就是這個Mapper的接口，編譯完成后會自動生成相應(yīng)的實現(xiàn)類

然后就可以直接用mapper進(jìn)行實體的轉(zhuǎn)換了

publicclassTest{

publicstaticvoidmain(String[]args){

Studentstudent=Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(newDate()).build();
System.out.println(student);
//這行代碼便是實際要用的代碼
StudentVOstudentVO=StudentMapper.INSTANCE.student2StudentVO(student);
System.out.println(studentVO);

}

}

mapper可以進(jìn)行字段映射，改變字段類型，指定格式化的方式，包括一些日期的默認(rèn)處理。

可以手動指定格式化的方法：

@Mapper
publicinterfaceStudentMapper{

StudentMapperINSTANCE=Mappers.getMapper(StudentMapper.class);

@Mapping(source="gender",target="gender")
@Mapping(source="birthday",target="birthday",dateFormat="yyyy-MM-ddHHss")
StudentVOstudent2StudentVO(Studentstudent);

defaultStringgetGenderName(GenderEnumgender){
returngender.getName();
}

}

上面只是最簡單的實體映射處理，下面介紹一些高級用法

1、List 轉(zhuǎn)換

屬性映射基于上面的mapping配置

@Mapper
publicinterfaceStudentMapper{

StudentMapperINSTANCE=Mappers.getMapper(StudentMapper.class);

@Mapping(source="gender.name",target="gender")
@Mapping(source="birthday",target="birthday",dateFormat="yyyy-MM-ddHHss")
StudentVOstudent2StudentVO(Studentstudent);


Liststudents2StudentVOs(ListstudentList);

}
publicstaticvoidmain(String[]args){

Studentstudent=Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(newDate()).build();

Listlist=newArrayList<>();
list.add(student);
Listresult=StudentMapper.INSTANCE.students2StudentVOs(list);
System.out.println(result);
}

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2、多對象轉(zhuǎn)換到一個對象

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
publicclassStudent{

privateStringname;
privateintage;
privateGenderEnumgender;
privateDoubleheight;
privateDatebirthday;

}
@Data
@AllArgsConstructor
@Builder
@NoArgsConstructor
publicclassCourse{

privateStringcourseName;
privateintsortNo;
privatelongid;

}
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
publicclassStudentVO{
privateStringname;
privateintage;
privateStringgender;
privateDoubleheight;
privateStringbirthday;
privateStringcourse;
}
@Mapper
publicinterfaceStudentMapper{

StudentMapperINSTANCE=Mappers.getMapper(StudentMapper.class);

@Mapping(source="student.gender.name",target="gender")
@Mapping(source="student.birthday",target="birthday",dateFormat="yyyy-MM-ddHHss")
@Mapping(source="course.courseName",target="course")
StudentVOstudentAndCourse2StudentVO(Studentstudent,Coursecourse);

}
publicclassTest{

publicstaticvoidmain(String[]args){

Studentstudent=Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(newDate()).build();
Coursecourse=Course.builder().id(1L).courseName("語文").build();

StudentVOstudentVO=StudentMapper.INSTANCE.studentAndCourse2StudentVO(student,course);
System.out.println(studentVO);
}

}

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3、默認(rèn)值

@Mapper
publicinterfaceStudentMapper{

StudentMapperINSTANCE=Mappers.getMapper(StudentMapper.class);

@Mapping(source="student.gender.name",target="gender")
@Mapping(source="student.birthday",target="birthday",dateFormat="yyyy-MM-ddHHss")
@Mapping(source="course.courseName",target="course")
@Mapping(target="name",source="student.name",defaultValue="張三")
StudentVOstudentAndCourse2StudentVO(Studentstudent,Coursecourse);

}