一款PO VO DTO 转换神器，求求你别在到处找工具类了！-技术圈

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.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"?

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

1.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 students2StudentVOs(List 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 list = new ArrayList<>();    list.add(student);    List result = StudentMapper.INSTANCE.students2StudentVOs(list);    System.out.println(result);}

2.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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