Use of org.mapstruct.Mapper

What is Mapper?

MapStruct is a code generator based on the idea of ​​convention over configuration.

Greatly simplifies conversion between Java bean types.

Why use mapstruct?

When JAVA is developed according to the traditional MVC or DDD model, the different bean types between layers of transmission will involve a large number of bean conversions, such as: DO, BO, DTO, entity, VO, etc.

What are the advantages and disadvantages of using mapstruct?

*Advantages:
mapstruct completes Bean conversion at compile time, which improves service performance compared with memory-based (BeanUtils.copy...).
Mapstruct completes the Bean conversion during compilation, and generates the corresponding xxximp.java file in the target directory after compilation. The code is transparent to developers, which is convenient for locating bugs

How to introduce mapstruct in the project

<!-- 引入pom依赖 -->
...
<properties>
	<lombok.version>1.18.16</lombok.version>
    <org.mapstruct.version>1.4.2.Final</org.mapstruct.version>
</properties>
...
<dependencies>
    <dependency>
        <groupId>org.mapstruct</groupId>
        <artifactId>mapstruct</artifactId>
        <version>${org.mapstruct.version}</version>
    </dependency>
</dependencies>
...
<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
                <annotationProcessorPaths>
                	<!-- other annotation processors -->
                    <path>
                        <groupId>org.projectlombok</groupId>
                        <artifactId>lombok</artifactId>
                        <version>${lombok.version}</version>
                    </path>
                    <path>
                        <groupId>org.mapstruct</groupId>
                        <artifactId>mapstruct-processor</artifactId>
                        <version>${org.mapstruct.version}</version>
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>
    </plugins>
</build>
...

How to use mapstruct (grammar description): Paste the code directly

Way 1

@Mapper 
public interface CarMapper {
    //静态成员
    CarMapper INSTANCE = Mappers.getMapper( CarMapper.class ); 
    
    // 转换函数的定义
    @Mapping(source = "numberOfSeats", target = "seatCount")
    CarDto carToCarDto(Car car); 2
}

Way 2

//将bean交给spring管理， --> componentModel = "spring"
//目标属性未匹配时系统忽略，不打印警告日志  -->unmappedTargetPolicy = ReportingPolicy.IGNORE
// 公共的转换组件引用  --> uses = {ConvertUtil.class}
@Mapper(unmappedTargetPolicy = ReportingPolicy.IGNORE, uses = {ConvertUtil.class}, componentModel = "spring")
public interface CarMapper {

    // 转换函数的定义
    @Mapping(source = "numberOfSeats", target = "seatCount")
    CarDto carToCarDto(Car car); 2
}

@Mapper syntax sample

// 示例小样1
	@Mapper(unmappedTargetPolicy = ReportingPolicy.IGNORE, uses = ConvertUtil.class, componentModel = "spring")
	
	// 指定默认值
	@Mapping(target = "name", source="name", defaultValue = "我是默认值") 
	
	// 使用java可执行代码或函数
	@Mapping(target = "name", expression = "java(\"OT\" + paramBean.getId())")
	
	// 使用常量代替默认值
	@Mapping(target = "stringConstant", constant = "Constant Value")
	
	//日期格式化
	@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
	// Integer 到 String的转换
	@Mapping(source = "price", numberFormat = "$#.00")
	//Date 转字符串
	@Mapping(source = "currentDate", dateFormat = "dd.MM.yyyy")
	

 	
 	@Mappings({
    	@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss"),
    	@Mapping(source = "name", target = "name")
    })

	@IterableMapping(dateFormat = "dd.MM.yyyy")
	List<String> dateToString(List<Date> dates)
	
	// 引用另一个映射器类
	@Mapper(uses = PrivateDateMapper.class)
	public class CartMapper {
    	CartDto cartToCartDto(Cart cart);
	}
	public class DateMapper {
    	public String asString(Date date) {
    		...	...
    	}
    	public Date toDate(String date) {
    		...	...
    	}
	}



// 示例小样2  DO 转 DTO
	public interface PersonDo2DtoMapping {
	    PersonDo2DtoMapping INSTANCE = Mappers.getMapper(PersonDo2DtoMapping.class);
	    
	    @Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
	    PersonDto do2dto(PersonDo personDo);
	}

// 示例小样3  DO集合 转 DTO集合：
	public interface PersonDo2DtoMapping {
	    PersonDo2DtoMapping INSTANCE = Mappers.getMapper(PersonDo2DtoMapping.class);
	    
	    @Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
	    PersonDto do2dto(PersonDo personDo);
	  
	  	// 会使用domain2dto方法进行对象list转换 
	  	//   	集合的bean的转换本质是:转换的时候调用了do2dto方法，也就是说mapsstruct能自动的使用合适的转换方法
	    List<PersonDto> listToList(List<PersonDo> people);
	}

//示例小样4 多个类型的 DO 转换为一个类型的 DTO
	public interface PersonDo2DtoMapping {
	    PersonDo2DtoMapping INSTANCE = Mappers.getMapper(PersonDo2DtoMapping.class);
	    
	    @Mapping(source = "psersonDo.birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
	    @Mapping(source = "userDo.name", target = "name")
	    PersonDto twoDoTOTwoDto(PersonDo personDo,UserDO userDo);
	}

//示例小样5 自定义DO 转 DTO 的映射规则
//		eg:比如的用户性别sex DO对应的是Integer类型{0:男,1:女}， DTO对应的是String类型{0:男,1:女}
	/**定义PersonSexConverterRule 转换规则类*/
	public class PersonSexConverterRule {
		public String intToString(int sex) {
	        if (sex == 0) {
	        	return "男";
	        } else {
		        return "女";
	        }
	    }
	}

	@Mapper(uses = PersonSexConverterRule.class)
	public interface PersonDo2DtoMapping {
		    PersonDo2DtoMapping INSTANCE = Mappers.getMapper(PersonDo2DtoMapping.class);
		    
		    // ?? 规则作用在哪个属性上，是根据属性类型进行规则匹配的？
		    @Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
		    PersonDto do2dto(PersonDo personDo);
		}

//示例小样6 spring整合:需要在映射接口的mapper注解中添加参数componentModel = "spring"
	@Mapper(uses = PersonSexConverterRule.class,componentModel = "spring")
	public interface PersonDo2DtoMapping {
		    PersonDo2DtoMapping INSTANCE = Mappers.getMapper(PersonDo2DtoMapping.class);
		    
		    // ?? 规则作用在哪个属性上，是根据属性类型进行规则匹配的？
		    @Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
		    PersonDto do2dto(PersonDo personDo);
		}