DDD-声明式复杂规则校验实践

当进行DDD编程过程中，有个非常繁琐，但又是非常重要的步骤：整理出某个实体的所有业务字段约束。

关于业务校验，业界已经有一些框架支持，如validator框架。但大部分人只用于参数校验，并未将其用于实体内。

本人整理出了一种声明式表达业务的方式。写起约束来个人感觉比较聚焦，从而可以辅助思考和整理约束。

直接上示例代码：
以下代码体现了一个品牌的业务约束和行为操作。

BrandNameDuplicateChecker：展示针对实体的复杂校验
BrandLogoChecker：展示针对实体单个字段的复杂校验
Spec：复杂校验注解声明，内部类SpecChecker是关键代码

品牌实体

@Data
@Setter(AccessLevel.PROTECTED)
@Accessors(chain = true)
@Spec(value = BrandNameDuplicateChecker.class) //复杂规则校验，一般涉及bean依赖的校验
public class Brand extends BaseEntity<Brand> {

  @ApiModelProperty("品牌ID")
  private Long id;

  @Size(min=1, max=100, message = "品牌名称字符数限制为[1,100]")
  @ApiModelProperty("品牌名称")
  private String name;

  @Spec(value = BrandLogoChecker.class)
  @Pattern(regexp = "(https?|ftp|file)://[-A-Za-z0-9+&@#/%?=~_|!:,.;]+[-A-Za-z0-9+&@#/%=~_|]", message = "logo必须为合法的URL")
  @Size(min=1, max = 128, message = "品牌名称长度必须在1-128字符内")
  @ApiModelProperty("品牌logo，为标准的URL图片格式")
  private String logo;

  @ApiModelProperty("排序分值")
  private Long score;

  @ApiModelProperty("是否隐藏")
  private Boolean hidden;

  @ApiModelProperty("版本号")
  private Long version;
  @ApiModelProperty("创建时间")
  private Date createdAt;
  @ApiModelProperty("更新时间")
  private Date updatedAt;

  protected Brand(){}
  
  
  public Brand(Long id, String name, String logo, Long score, Boolean hidden) {
    this.id = id;
    this.name = name;
    this.logo = logo;
    this.score = score;
    this.hidden = hidden;
    
    version = 0L;
    createdAt = new Date();
    updatedAt = new Date();
    
    this.validate(); //触发校验
  }
  
  public Brand changeName(String name){
    
    Brand toUpdate = new Brand().setId(this.id).setName(name);
    toUpdate.validate("name");
    DomainRegistry.bean(BrandNameDuplicateChecker.class).check(toUpdate);
    
    this.name = name;
    return this;
  }
  
  public Brand changeLogo(String logo){
    
    Brand toUpdate = new Brand().setId(this.id).setLogo(logo);
    toUpdate.validate("logo");
    
    this.logo = logo;
    return this;
  }
  
  public Brand changeScore(Long score){
    
    Brand toUpdate = new Brand().setId(this.id).setScore(score);
    toUpdate.validate("score");
    
    this.score = score;
    return this;
  }
  
  public Brand hidden(){
    
    this.hidden = true;
    return this;
  }
  
  public Brand visible(){
    
    this.hidden = false;
    return this;
  }

  public static Brand load(Long id){
    return Optional.ofNullable(DomainRegistry.repo(BrandRepo.class).findById(id))
        .orElseThrow(()->new BusinessException("品牌不存在"));
  }
}

针对实体本身的复杂校验

@Component
@Slf4j
public class BrandNameDuplicateChecker implements Checker<Brand>{
  
  @Autowired
  @Setter
  private BrandRepo brandRepo;
  
  @Override
  public void check(Brand brand) {
    if(Strings.isNullOrEmpty(brand.getName())){
      return;
    }
    Brand exist = brandRepo.findByName(brand.getName());
    if(exist!=null && ! Objects.equals(brand.getId(), exist.getId())){
      throw new BusinessException("品牌名称已经被使用");
    }
  }
}

针对实体字段的复杂校验

@Component
public class BrandLogoChecker implements Checker<String> {
  
  @Autowired
  @Setter
  private PhotoUrlChecker photoUrlChecker;
  
  @Override
  public void check(String logo) {
    if(photoUrlChecker.invalid(logo)){
      throw new BusinessException("品牌Logo的URL不合法");
    }
  }
}

复杂校验实现

@Target({ ElementType.FIELD, ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Constraint(validatedBy = { Spec.SpecChecker.class })
public @interface Spec {
  
  Class<? extends Checker>[] value();
  
  String message() default "字段不符合条件约束";
  
  Class<?>[] groups() default {};
  
  Class<? extends Payload>[] payload() default {};
  
  
  @Slf4j
  public static class SpecChecker implements ConstraintValidator<Spec, Object> {
    
    Spec annotation;
    
    List<Class<? extends Checker>> checkerClasses;
  
    Map<Class<? extends Checker>, ? extends Checker> allCheckers;
    
    @Override
    public void initialize(Spec constraintAnnotation) {
      annotation = constraintAnnotation;
      checkerClasses = Arrays.asList(annotation.value());
      allCheckers = DomainRegistry.beanMap(Checker.class)
          .values().stream()
          .collect(Collectors.toMap(Checker::getClass, Function.identity()));
    }
    
    @Override
    public boolean isValid(Object object, ConstraintValidatorContext constraintValidatorContext) {
      try {
        StringBuilder sb = new StringBuilder();
        checkerClasses.forEach(c->{
          Checker checker = allCheckers.get(c);
          if(checker!=null){
            try {
              checker.check(object);
            }catch (Exception e){
              sb.append(e.getMessage()).append(" ");
            }
          }
        });
        if(sb.length()>0) {
          constraintValidatorContext.disableDefaultConstraintViolation();
          constraintValidatorContext
              .buildConstraintViolationWithTemplate(sb.toString())
              .addConstraintViolation();
          return false;
        }else{
          return true;
        }
      }catch (Exception e){
        log.warn("", e);
        return false;
      }
    }
    
  }
}

应用服务

  @Transactional
  public Brand create(@Valid BrandCreateParam param){
    
    Brand brand = new Brand(
        idGen.generateId(),
        param.getName(),
        param.getLogo(),
        param.getScore(),
        param.getHidden()
    );
    
    brandRepo.create(brand);
    
    return brand;
  }

具体代码已经放在github上：Brand.java