Java多态在Spring Boot 3中的实际应用实例教程

src/main/java/com/example/demo/
├── controller/
├── service/
│   ├── impl/
│   └── PaymentService.java
├── config/
└── DemoApplication.java

public interface PaymentService {
    String pay(double amount);
    String getType();
}

@Service("alipay")
public class AlipayService implements PaymentService {
    @Override
    public String pay(double amount) {
        return String.format("支付宝支付成功，金额：%.2f元", amount);
    }
    @Override
    public String getType() {
        return "alipay";
    }
}

@Service("wechat")
public class WechatPayService implements PaymentService {
    @Override
    public String pay(double amount) {
        return String.format("微信支付成功，金额：%.2f元", amount);
    }
    @Override
    public String getType() {
        return "wechat";
    }
}

@Service("bank")
public class BankPayService implements PaymentService {
    @Override
    public String pay(double amount) {
        return String.format("银行卡支付成功，金额：%.2f元", amount);
    }
    @Override
    public String getType() {
        return "bank";
    }
}

@RestController
public class PaymentController {
    @Autowired
    @Qualifier("alipay") // 指定注入的具体实现
    private PaymentService paymentService;
    @PostMapping("/pay")
    public String doPay(@RequestParam double amount) {
        return paymentService.pay(amount);
    }
}

@RestController
public class PaymentController {
    @Autowired
    private Map<String, PaymentService> paymentServiceMap;
    @PostMapping("/pay/{type}")
    public String doPay(@PathVariable String type, 
                       @RequestParam double amount) {
        PaymentService service = paymentServiceMap.get(type);
        if (service == null) {
            return "不支持的支付方式";
        }
        return service.pay(amount);
    }
}

@Component
public class PaymentStrategyFactory {
    @Autowired
    private Map<String, PaymentService> paymentServiceMap;
    public PaymentService getStrategy(String type) {
        return paymentServiceMap.get(type);
    }
}

@RestController
public class PaymentController {
    @Autowired
    private PaymentStrategyFactory strategyFactory;
    @PostMapping("/pay/strategy/{type}")
    public String payByStrategy(@PathVariable String type,
                              @RequestParam double amount) {
        PaymentService service = strategyFactory.getStrategy(type);
        if (service == null) {
            return "支付方式不存在";
        }
        return service.pay(amount);
    }
}

@Service
@ConditionalOnProperty(name = "payment.type", havingValue = "alipay")
public class AlipayConditionalService implements PaymentService {
    // 实现方法
}
@Service
@ConditionalOnProperty(name = "payment.type", havingValue = "wechat")
public class WechatConditionalService implements PaymentService {
    // 实现方法
}

payment:
  type: alipay  # 或 wechat

@Aspect
@Component
public class PaymentLogAspect {
    @Pointcut("execution(* com.example.demo.service.PaymentService.pay(..))")
    public void paymentPointcut() {}
    @Before("paymentPointcut()")
    public void beforePay(JoinPoint joinPoint) {
        Object target = joinPoint.getTarget();
        if (target instanceof PaymentService) {
            PaymentService service = (PaymentService) target;
            System.out.println("开始执行" + service.getType() + "支付");
        }
    }
}

@SpringBootTest
public class PaymentServiceTest {
    @Mock
    private PaymentService paymentService;
    @Test
    public void testPay() {
        when(paymentService.pay(100.0)).thenReturn("支付成功");
        String result = paymentService.pay(100.0);
        assertEquals("支付成功", result);
    }
}

@Test
public void testStrategySelection() {
    PaymentService alipay = new AlipayService();
    PaymentService wechat = new WechatPayService();
    assertNotEquals(alipay.pay(100), wechat.pay(100));
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface PaymentType {
    String value();
}

@Service
@PaymentType("alipay")
public class AlipayService implements PaymentService {
    // 实现
}

@Component
public class PaymentAnnotationScanner {
    @Autowired
    private ApplicationContext context;
    public Map<String, PaymentService> getPaymentServices() {
        Map<String, PaymentService> services = new HashMap<>();
        String[] beanNames = context.getBeanNamesForType(PaymentService.class);
        for (String beanName : beanNames) {
            PaymentService service = (PaymentService) context.getBean(beanName);
            PaymentType annotation = service.getClass().getAnnotation(PaymentType.class);
            if (annotation != null) {
                services.put(annotation.value(), service);
            }
        }
        return services;
    }
}

public PaymentService getStrategy(String type) {
    PaymentService service = paymentServiceMap.get(type);
    if (service == null) {
        throw new IllegalArgumentException("不支持的支付方式: " + type);
    }
    return service;
}

public enum PaymentTypeEnum {
    ALIPAY("alipay"),
    WECHAT("wechat"),
    BANK("bank");
    private final String code;
    PaymentTypeEnum(String code) {
        this.code = code;
    }
    public String getCode() {
        return code;
    }
}

@Service
@Primary // 指定为默认支付方式
public class DefaultPaymentService implements PaymentService {
    // ... 实现逻辑
}