介绍一个开源项目 mapstruct

正文如下

来源：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-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>

<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <annotationProcessorPaths>
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                            <version>${org.projectlombok.version}</version>
                        </path>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>${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@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

@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);

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);
}


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

@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);

}