@Service 标记的类不存在注释数据

Question

我正在尝试实现解析器模式（策略模式）。

所以我有一个自定义注释 @PaymentTypeValue

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface PaymentTypeValue {
    PaymentType[] value();
}

和 PaymentType 作为枚举类

public enum PaymentType{
CASH, CARD, NET_BANKING, UPI, WALLET;
}

，现在我有接口 PaymentService

public interface PaymentService {
   void process();
}

并有它的 5 个实现，其中一个就像

@Service
@PaymentTypeValue({PaymentTypeValue.CASH})
public class CashPaymentService implements PaymentService {
  @Override
  void process(){
    //some logic
  }
}

我 现在问题出

@Component
public class PaymentServiceResolver {

    private static final Logger log = getLogger(PaymentServiceResolver.class);

    @Autowired
    private List<PaymentService> paymentServices;

    private final Map<PaymentType, PaymentService> paymentServiceMap = new EnumMap<>(PaymentType.class);

    @PostConstruct
    public void init() {
        paymentServices.forEach(paymentService -> {
                    PaymentTypeValue annotation = paymentService.getClass().getAnnotation(PaymentTypeValue.class);
                    if (annotation != null && annotation.value() != null) {
                        PaymentType[] paymentTypes = annotation.value();
                        Arrays.stream(paymentTypes).forEach(paymentType -> {
                            paymentServiceMap.put(paymentType, paymentService);
                        });
                    } else {
                        log.error("paymentService {} is missing a necessary annotation",
                                paymentService.getClass().getName());
                        log.error("This paymentService cannot be initialized");
//                        throw new IllegalStateException("paymentService is missing a necessary annotation for " + paymentService.getClass().getName());
                    }
                }
        );
    }

    public PaymentService resolvePaymentService(PaymentType paymentType) {
        PaymentService paymentService = paymentServiceMap.get(paymentType);
        if (paymentService != null) {
            return paymentService;
        } else {
            String message = "Could not find paymentService for " + paymentType;
            log.error(message);
            throw new RuntimeException(message);
        }
    }
}

在 init() 方法中，PaymentService 的所有服务实现都出现在列表中，但是当我尝试查找注释时，它给出了 null。 我检查了 paymentService.getClass() 方法的值，其中annotationData 有 0 个注释。如果我自动装配 PaymentService 的任何特定实现，那么我就能够获取注释值。请帮助我理解我在这里缺少什么？

Answer 1

注释方法使事情变得复杂，我会尽力避免这种情况。没有注释的更简单的解决方案，假设 PaymentType 和服务实现之间存在 1:1 映射：

1. 向服务接口添加函数 boolean canHandle(PaymentType) 。
2. 解析器使用该信息来定位匹配的服务。

接口：

public interface PaymentService {

    boolean canHandle(PaymentType paymentType);

    void process();
}

服务实现：

@Service
public class CashPaymentService implements PaymentService {

    @Override
    public boolean canHandle(PaymentType paymentType) {
        return PaymentType.CASH.equals(paymentType);
    }

    @Override
    public void process() {
        // processing...
    }
}

服务定位器：

@Component
public class PaymentServiceResolver {

    private final List<PaymentService> paymentServices;
    private final Map<PaymentType,PaymentService> serviceMapping = new ConcurrentHashMap<>(5);

    @Autowired
    public PaymentServiceResolver(List<PaymentService> paymentServices) {
        this.paymentServices = paymentServices;
    }

    public PaymentService resolve(PaymentType paymentType) {
        return serviceMapping.computeIfAbsent(paymentType, resolveInternal());
    }

    private Function<PaymentType, PaymentService> resolveInternal() {
        return paymentType ->
                paymentServices.stream()
                        .filter(service -> service.canHandle(paymentType))
                        .findFirst()
                        .orElseThrow(() -> new IllegalStateException("Unsupported payment type: " + paymentType));
    }
}

您可以向解析器添加更多验证逻辑，以在 Spring 初始化阶段检查每个 PaymentType 是否有可用的实现。