别再用BeanUtils了，这款PO VO DTO转换神器不香么？

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老铁们是不是经常为写一些实体转换的原始代码感到头疼，尤其是实体字段特别多的时候。介绍一个开源项目 mapstruct ，可以轻松优雅的进行转换，简化你的代码。当然有的人喜欢写get set，或者用BeanUtils 进行复制，代码只是工具，本文只是提供一种思路。

先贴下官网地址吧：https://mapstruct.org/

废话不多说，上代码：

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>

关于lombok和mapstruct的版本兼容问题多说几句，maven插件要使用3.6.0版本以上、lombok使用1.16.16版本以上，另外编译的lombok mapstruct的插件不要忘了加上。否则会出现下面的错误：No property named "aaa" exists in source parameter(s). Did you mean "null"?

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这种异常就是lombok编译异常导致缺少get setter方法造成的。还有就是缺少构造函数也会抛异常。

@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);

}

实体类是开发过程少不了的，就算是用工具生成肯定也是要有的，需要手写的部分就是这个Mapper的接口，编译完成后会自动生成相应的实现类

然后就可以直接用mapper进行实体的转换了

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);
//这行代码便是实际要用的代码
StudentVOstudentVO=StudentMapper.INSTANCE.student2StudentVO(student);
System.out.println(studentVO);

}

}

mapper可以进行字段映射，改变字段类型，指定格式化的方式，包括一些日期的默认处理。

可以手动指定格式化的方法：

@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();
}

}

上面只是最简单的实体映射处理，下面介绍一些高级用法

1、List 转换

属性映射基于上面的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、多对象转换到一个对象

@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("语文").build();

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

}

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3、默认值

@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="张三")
StudentVOstudentAndCourse2StudentVO(Studentstudent,Coursecourse);

}

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