Java微服务韧性设计模式：熔断、限流与降级实战

// 示例：使用Resilience4j配置一个熔断器
CircuitBreakerConfig circuitBreakerConfig = CircuitBreakerConfig.custom()
    .failureRateThreshold(50) // 失败率达到50%时熔断
    .waitDurationInOpenState(Duration.ofSeconds(60)) // 熔断打开后等待60秒
    .slidingWindowType(CircuitBreakerConfig.SlidingWindowType.COUNT_BASED) // 基于请求数统计
    .slidingWindowSize(100) // 统计最近100个请求
    .minimumNumberOfCalls(10) // 至少10个请求后才开始计算失败率
    .build();

CircuitBreakerRegistry circuitBreakerRegistry = CircuitBreakerRegistry.of(circuitBreakerConfig);
CircuitBreaker circuitBreaker = circuitBreakerRegistry.circuitBreaker("myService");

// 包装你的服务调用
Supplier<String> decoratedSupplier = CircuitBreaker.decorateSupplier(circuitBreaker, () -> myService.callExternalApi());

// 执行调用
try {
    String result = decoratedSupplier.get();
    System.out.println("Service call successful: " + result);
} catch (CallNotPermittedException e) {
    // 熔断器打开，请求被拒绝
    System.err.println("Circuit Breaker is OPEN, call not permitted.");
} catch (Exception e) {
    // 其他异常处理
    System.err.println("Service call failed: " + e.getMessage());
}

RateLimiter

RateLimiter

// 示例：使用Resilience4j配置一个限流器
RateLimiterConfig config = RateLimiterConfig.custom()
    .limitRefreshPeriod(Duration.ofSeconds(1)) // 每秒刷新一次令牌
    .limitForPeriod(10) // 每秒允许10个请求
    .timeoutDuration(Duration.ofSeconds(0)) // 获取令牌的等待时间，0表示不等待
    .build();

RateLimiterRegistry rateLimiterRegistry = RateLimiterRegistry.of(config);
RateLimiter rateLimiter = rateLimiterRegistry.rateLimiter("myApiRateLimiter");

// 包装你的服务调用
Supplier<String> decoratedSupplier = RateLimiter.decorateSupplier(rateLimiter, () -> myService.processRequest());

for (int i = 0; i < 20; i++) {
    try {
        String result = decoratedSupplier.get();
        System.out.println("Request " + i + " processed: " + result);
    } catch (RequestNotPermitted e) {
        System.err.println("Request " + i + " rejected by Rate Limiter.");
    } catch (Exception e) {
        System.err.println("Request " + i + " failed: " + e.getMessage());
    }
    // 模拟请求间隔
    try {
        Thread.sleep(50);
    } catch (InterruptedException ex) {
        Thread.currentThread().interrupt();
    }
}

fallbackMethod

import io.resilience4j.circuitbreaker.annotation.CircuitBreaker;
import io.resilience4j.ratelimiter.annotation.RateLimiter;
import org.springframework.stereotype.Service;

@Service
public class ProductService {

    // 模拟一个外部API调用
    public String getProductDetails(String productId) {
        // 模拟调用失败或超时
        if (Math.random() > 0.7) { // 30%的概率失败
            throw new RuntimeException("External service unavailable!");
        }
        return "Details for product " + productId + " from external API.";
    }

    // 结合熔断和降级
    @CircuitBreaker(name = "productService", fallbackMethod = "getProductDetailsFallback")
    public String getProductDetailsWithCircuitBreaker(String productId) {
        return getProductDetails(productId);
    }

    // 结合限流和降级
    @RateLimiter(name = "productServiceRateLimiter", fallbackMethod = "getProductDetailsFallback")
    public String getProductDetailsWithRateLimiter(String productId) {
        return getProductDetails(productId);
    }

    // 降级方法
    public String getProductDetailsFallback(String productId, Throwable t) {
        System.err.println("Falling back for product " + productId + " due to: " + t.getMessage());
        // 返回默认值或缓存数据
        return "Default details for product " + productId + " (cached or simplified).";
    }

    // 另一个降级方法，可以处理特定异常
    public String getProductDetailsFallback(String productId, RuntimeException e) {
        System.err.println("Specific fallback for RuntimeException for product " + productId + ": " + e.getMessage());
        return "Simplified details for product " + productId + " due to runtime error.";
    }
}