软件简介

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);