策略模式+工厂模式
public interface PaymentService {
    void processPayment(BigDecimal amount);
}

@Service("ALIPAY")
public class AlipayService implements PaymentService {
    @Override
    public void processPayment(BigDecimal amount) {
        System.out.println("支付宝支付: " + amount);
    }
}

@Service("WECHAT")
public class WechatPayService implements PaymentService {
    @Override
    public void processPayment(BigDecimal amount) {
        System.out.println("微信支付: " + amount);
    }
}

@Component
public class PaymentServiceFactory {
    private final Map<String, PaymentService> paymentServices;

    // 自动注入所有 PaymentService 实现类
    @Autowired
    public PaymentServiceFactory(Map<String, PaymentService> paymentServices) {
        this.paymentServices = paymentServices;
    }

    // 根据 type 获取对应的 Service
    public PaymentService getService(String type) {
        PaymentService service = paymentServices.get(type);
        if (service == null) {
            throw new IllegalArgumentException("无效支付类型: " + type);
        }
        return service;
    }
}

@RestController
public class PaymentController {
    @Autowired
    private PaymentServiceFactory paymentServiceFactory;

    @PostMapping("/pay")
    public String pay(@RequestParam String type, @RequestParam BigDecimal amount) {
        PaymentService service = paymentServiceFactory.getService(type);
        service.processPayment(amount);
        return "支付成功";
    }
}
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自定义注解 + 动态映射
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface PaymentType {
    String value();
}

@Service
@PaymentType("ALIPAY")
public class AlipayService implements PaymentService {
    @Override
    public void processPayment(BigDecimal amount) {
        System.out.println("支付宝支付: " + amount);
    }
}

@Service
@PaymentType("WECHAT")
public class WechatPayService implements PaymentService {
    @Override
    public void processPayment(BigDecimal amount) {
        System.out.println("微信支付: " + amount);
    }
}

@Component
public class PaymentServiceFactory {
    private final Map<String, PaymentService> paymentServices = new HashMap<>();

    // 初始化时扫描所有带有 @PaymentType 注解的 Bean
    @Autowired
    public void initPaymentServices(List<PaymentService> services) {
        for (PaymentService service : services) {
            PaymentType annotation = service.getClass().getAnnotation(PaymentType.class);
            if (annotation != null) {
                paymentServices.put(annotation.value(), service);
            }
        }
    }

    public PaymentService getService(String type) {
        PaymentService service = paymentServices.get(type);
        if (service == null) {
            throw new IllegalArgumentException("无效支付类型: " + type);
        }
        return service;
    }
    }
}

@RestController
public class PaymentController {
    @Autowired
    private PaymentServiceFactory paymentServiceFactory;  // 注入工厂类:ml-citation{ref="4" data="citationList"}

    @PostMapping("/pay")
    public ResponseEntity<?> processPayment(@RequestParam String type, @RequestParam BigDecimal amount) {
        // 根据 type 获取具体 Service 实现类
        PaymentService service = paymentServiceFactory.getService(type);  
        service.processPayment(amount);
        return ResponseEntity.ok("支付成功");
    }
}