一款PO VO DTO 转换神器，求求你别在到处找工具类了！

作者：bettermann toutiao.com/i6891531055631696395/

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.sourceEncodingUTF-8/project.build.sourceEncoding
        maven.compiler.source1.8/maven.compiler.source
        maven.compiler.target1.8/maven.compiler.target
        org.mapstruct.version1.4.1.Final/org.mapstruct.version
        org.projectlombok.version1.18.12/org.projectlombok.version
/properties

dependencies
        dependency
            groupIdorg.mapstruct/groupId
            artifactIdmapstruct/artifactId
            version${org.mapstruct.version}/version
        /dependency

        !-- lombok dependencies should not end up on classpath --
        dependency
            groupIdorg.projectlombok/groupId
            artifactIdlombok/artifactId
            version${org.projectlombok.version}/version
            scopeprovided/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
            groupIdorg.mapstruct/groupId
            artifactIdmapstruct-processor/artifactId
            version${org.mapstruct.version}/version
            scopeprovided/scope
        /dependency

/dependencies

build
        plugins
            plugin
                groupIdorg.apache.maven.plugins/groupId
                artifactIdmaven-compiler-plugin/artifactId
                version3.8.1/version
                configuration
                    source1.8/source
                    target1.8/target
                    annotationProcessorPaths
                        path
                            groupIdorg.projectlombok/groupId
                            artifactIdlombok/artifactId
                            version${org.projectlombok.version}/version
                        /path
                        path
                            groupIdorg.mapstruct/groupId
                            artifactIdmapstruct-processor/artifactId
                            version${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”?

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
public 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
@NoArgsConstructor
public class StudentVO {
    private String name;
    private int age;
    private String gender;
    private Double height;
    private String birthday;
}
@Mapper
public 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：

@Mapper
public 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

1.List 转换

属性映射基于上面的mapping配置

@Mapper
public 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);


    ListStudentVO students2StudentVOs(ListStudent 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();

    ListStudent list = new ArrayList();
    list.add(student);
    ListStudentVO result = StudentMapper.INSTANCE.students2StudentVOs(list);
    System.out.println(result);
}

2.多对象转换到一个对象

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class Student {

    private String name;
    private int age;
    private GenderEnum gender;
    private Double height;
    private Date birthday;

}
@Data
@AllArgsConstructor
@Builder
@NoArgsConstructor
public class Course {

    private String courseName;
    private int sortNo;
    private long id;

}
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class StudentVO {
    private String name;
    private int age;
    private String gender;
    private Double height;
    private String birthday;
    private String course;
}
@Mapper
public 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

@Mapper
public 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);

}

END

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原文始发于微信公众号（Java笔记虾）：一款PO VO DTO 转换神器，求求你别在到处找工具类了！