轻量级的容错组件 Resilience4j（stratus容错服务器官网）

Resilience4j 是一个轻量级的容错组件，其灵感来自于 Hystrix，但主要为 Java 8 和函数式编程所设计。轻量级体现在其只用 Vavr 库（前身是 Javaslang），没有任何外部依赖。而 Hystrix 依赖了 Archaius ，Archaius 本身又依赖很多第三方包，例如 Guava、Apache Commons Configuration 等。

限速组件架构：

Resilience4j 提供了如下几款核心组件

• resilience4j-circuitbreaker: Circuit breaking
• resilience4j-ratelimiter: Rate limiting
• resilience4j-bulkhead: Bulkheading
• resilience4j-retry: Automatic retrying (sync and async)
• resilience4j-cache: Response caching

附件组件包括：

• resilience4j-reactor: Spring Reactor adapter
• resilience4j-rxjava2: RxJava2 adapter
• resilience4j-micrometer: Micrometer Metrics exporter
• resilience4j-metrics: Dropwizard Metrics exporter
• resilience4j-prometheus: Prometheus Metrics exporter
• resilience4j-spring-boot: Spring Boot Starter
• resilience4j-ratpack: Ratpack Starter
• resilience4j-retrofit: Retrofit Call Adapter Factories
• resilience4j-vertx: Vertx Future decorator
• resilience4j-consumer: Circular Buffer Event consumer

使用示例：

• CircuitBreaker, Retry and Fallback
• RateLimiter
• Bulkhead
• Cache
• Metrics
• Consume emitted events

使用 Resilience4j 实现请求调用频率限制的示例代码：

// Create a custom RateLimiter configuration
RateLimiterConfig config = RateLimiterConfig.custom()
 .timeoutDuration(Duration.ofMillis(100))
 .limitRefreshPeriod(Duration.ofSeconds(1))
 .limitForPeriod(1)
 .build();
// Create a RateLimiter
RateLimiter rateLimiter = RateLimiter.of("backendName", config);
// Decorate your call to BackendService.doSomething()
Supplier<String> restrictedSupplier = RateLimiter
 .decorateSupplier(rateLimiter, backendService::doSomething);
// First call is successful
Try<String> firstTry = Try.ofSupplier(restrictedSupplier);
assertThat(firstTry.isSuccess()).isTrue();
// Second call fails, because the call was not permitted
Try<String> secondTry = Try.of(restrictedSupplier);
assertThat(secondTry.isFailure()).isTrue();
assertThat(secondTry.getCause()).isInstanceOf(RequestNotPermitted.class);