//源对象
@Data
public class EntityH implements Serializable{
    private Integer valH;
}

//目标对象
@Data
public class EntityI implements Serializable{
    private Integer valH;
}

//转换方法
@Mapper
public interface ExpressionMapper {
    ExpressionMapper INSTANCE = Mappers.getMapper(ExpressionMapper.class);
    @Mappings({
            @Mapping(target = "valH", expression = "java(entityH.getValH() + 1 + (int)(Math.random()*5))"),
    })
    EntityI entityGtoI(EntityH entityH);
}

//调用方法
@SpringBootApplication
public class DemoApplication {
  public static void main(String[] args) throws ParseException {
      entityH.setValH(5);
      entityI = ExpressionMapper.INSTANCE.entityGtoI(entityH);
      System.out.println(entityI.toString());
      SpringApplication.run(DemoApplication.class, args);
  }

//结果

image.png

使用场景
目标对象需要对源对象的字段做一些简单处理，类似金额相加等等。