别再用 BeanUtils 了，这款 PO VO DTO 转换神器不香么？

> *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>

<dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>${org.projectlombok.version}</version>
            <scope>provided</scope>
        </dependency>

<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。学习资料：[Java进阶视频资源](https://mp.weixin.qq.com/s/jGEkHTf2X8l-wUenc-PpEw)

```
@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

![MarkerHub](https://image-1300566513.cos.ap-guangzhou.myqcloud.com/upload/images/20211126/6e017074aa6743d79dc90e6aea1b7b71.png)

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);

}

}
```

![MarkerHub](https://image-1300566513.cos.ap-guangzhou.myqcloud.com/upload/images/20211126/6e017074aa6743d79dc90e6aea1b7b71.png)

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);

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);
}
```

![MarkerHub](https://image-1300566513.cos.ap-guangzhou.myqcloud.com/upload/images/20211126/ea7f3e1b3de248ac8f280471c1b1b636.png)

### 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);
    }

}
```

![MarkerHub](https://image-1300566513.cos.ap-guangzhou.myqcloud.com/upload/images/20211126/a98cb6f212854f97b958d70df9a3bce9.png)

### 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);

}
```

![MarkerHub](https://image-1300566513.cos.ap-guangzhou.myqcloud.com/upload/images/20211126/78092c3679e74346aa2e4c4612f70b94.png)

别再用 BeanUtils 了，这款 PO VO DTO 转换神器不香么？

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