1、前言
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：mapstruct.org/
废话不多说，上代码：
pom.xml 配置：
<properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <maven.compiler.source>1.8</maven.compiler.source> <maven.compiler.target>1.8</maven.compiler.target> <org.mapstruct.version>1.4.1.Final</org.mapstruct.version> <org.projectlombok.version>1.18.12</org.projectlombok.version></properties><dependencies> <dependency> <groupId>org.mapstruct</groupId> <artifactId>mapstruct</artifactId> <version>${org.mapstruct.version}</version> </dependency> <!-- lombok dependencies should not end up on classpath --> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>${org.projectlombok.version}</version> <scope>provided</scope> </dependency> <!-- idea 2018.1.1 之前的版本需要添加下面的配置，后期的版本就不需要了，可以注释掉，我自己用的2019.3 --> <dependency> <groupId>org.mapstruct</groupId> <artifactId>mapstruct-processor</artifactId> <version>${org.mapstruct.version}</version> <scope>provided</scope> </dependency></dependencies>
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"?
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@NoArgsConstructorpublic class Student { private String name; private int age; private GenderEnum gender; private Double height; private Date birthday;}public enum GenderEnum { Male("1", "男"), Female("0", "女"); private String code; private String name; public String getCode() { return this.code; } public String getName() { return this.name; } GenderEnum(String code, String name) { this.code = code; this.name = name; }}@Data@Builder@AllArgsConstructor@NoArgsConstructorpublic class StudentVO { private String name; private int age; private String gender; private Double height; private String birthday;}@Mapperpublic interface StudentMapper { StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class); @Mapping(source = "gender.name", target = "gender") @Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss") StudentVO student2StudentVO(Student student);}
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
public class Test { public static void main(String[] args) { Student student = Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(new Date()).build(); System.out.println(student); //这行代码便是实际要用的代码 StudentVO studentVO = 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：
@Mapperpublic interface StudentMapper { StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class); @Mapping(source = "gender", target = "gender") @Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss") StudentVO student2StudentVO(Student student); default String getGenderName(GenderEnum gender) { return gender.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：
2、List 转换
属性映射基于上面的mapping配置
@Mapperpublic interface StudentMapper { StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class); @Mapping(source = "gender.name", target = "gender") @Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss") StudentVO student2StudentVO(Student student); List<StudentVO> students2StudentVOs(List<Student> studentList);}public static void main(String[] args) { Student student = Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(new Date()).build(); List<Student> list = new ArrayList<>(); list.add(student); List<StudentVO> result = StudentMapper.INSTANCE.students2StudentVOs(list); System.out.println(result);}
3、多对象转换到一个对象
@Data@Builder@AllArgsConstructor@NoArgsConstructorpublic class Student { private String name; private int age; private GenderEnum gender; private Double height; private Date birthday;}@Data@AllArgsConstructor@Builder@NoArgsConstructorpublic class Course { private String courseName; private int sortNo; private long id;}@Data@Builder@AllArgsConstructor@NoArgsConstructorpublic class StudentVO { private String name; private int age; private String gender; private Double height; private String birthday; private String course;}@Mapperpublic interface StudentMapper { StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class); @Mapping(source = "student.gender.name", target = "gender") @Mapping(source = "student.birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss") @Mapping(source = "course.courseName", target = "course") StudentVO studentAndCourse2StudentVO(Student student, Course course);}public class Test { public static void main(String[] args) { Student student = Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(new Date()).build(); Course course = Course.builder().id(1L).courseName("语文").build(); StudentVO studentVO = StudentMapper.INSTANCE.studentAndCourse2StudentVO(student, course); System.out.println(studentVO); }}
3、默认值
@Mapperpublic interface StudentMapper { StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class); @Mapping(source = "student.gender.name", target = "gender") @Mapping(source = "student.birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss") @Mapping(source = "course.courseName", target = "course") @Mapping(target = "name", source = "student.name", defaultValue = "张三") StudentVO studentAndCourse2StudentVO(Student student, Course course);}
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