1. 环境配置

1.1 Apache Maven

Maven配置

<properties>
    <org.mapstruct.version>1.4.2.Final</org.mapstruct.version>
</properties>
...
<dependencies>
    <dependency>
        <groupId>org.mapstruct</groupId>
        <artifactId>mapstruct</artifactId>
        <version>${org.mapstruct.version}</version>
    </dependency>
</dependencies>
...
<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
                <annotationProcessorPaths>
                    <path>
                        <groupId>org.mapstruct</groupId>
                        <artifactId>mapstruct-processor</artifactId>
                        <version>${org.mapstruct.version}</version>
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>
    </plugins>
</build>
...

2. 定义Mapper

2.1. 基本mappings

定义一个mapper, 只需要简单的定义一个java接口, 定义上映射方法, 给方法加上 org.mapstruct.Mapper 注解.

• 例. 使用Java接口来定义一个mapper

  import org.mapstruct.Mapper
  @Mapper
  public interface CarMapper {
    @Mapping(source = "make", target = "manufacturer")
    @Mapping(source = "numberOfSeats", target = "seatCount")
    CarDto carToCarDto(Car car);
    @Mapping(source = "name", target = "fullName")
    PersonDto personToPersonDto(Person person);
  }

@Mapper注解会触发MapStruct代码生成器在build阶段, 生成一个 CarMapper 接口的实现.
Car 到 CarDto 的映射:

• 属性name相同, 会自动隐式映射.
• 属性name不同, 可以通过 @Mapping 注解手动指定映射关系.
• 通过@BeanMapping(ignoreByDefault = true) 来禁用自动默认映射, 要求必须要用 @Mapping 这种方式显式指定映射关系.

看一下自动生成的代码 carToCarDto()

• 例: MapStruct生成的代码

  // GENERATED CODE
  public class CarMapperImpl implements CarMapper {
    @Override
    public CarDto carToCarDto(Car car) {
        if ( car == null ) {
            return null;
        }
        CarDto carDto = new CarDto();
        if ( car.getFeatures() != null ) {
            carDto.setFeatures( new ArrayList<String>( car.getFeatures() ) );
        }
        carDto.setManufacturer( car.getMake() );
        carDto.setSeatCount( car.getNumberOfSeats() );
        carDto.setDriver( personToPersonDto( car.getDriver() ) );
        carDto.setPrice( String.valueOf( car.getPrice() ) );
        if ( car.getCategory() != null ) {
            carDto.setCategory( car.getCategory().toString() );
        }
        carDto.setEngine( engineToEngineDto( car.getEngine() ) );
        return carDto;
    }
    @Override
    public PersonDto personToPersonDto(Person person) {
        //...
    }
    private EngineDto engineToEngineDto(Engine engine) {
        if ( engine == null ) {
            return null;
        }
        EngineDto engineDto = new EngineDto();
        engineDto.setHorsePower(engine.getHorsePower());
        engineDto.setFuel(engine.getFuel());
        return engineDto;
    }
  }