聊聊spring cloud netflix的HystrixCommands

序

本文主要研究一下spring cloud netflix的HystrixCommands。

maven

<dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
            <version>2.0.0.RELEASE</version>
        </dependency>

這個組件對hystrix進行了封裝了，2.0.0.RELEASE全面支持了Reactor的Reactive Streams。

spring-cloud-starter-netflix-hystrix/pom.xml

spring-cloud-starter-netflix-hystrix-2.0.0.RELEASE.jar!/META-INF/maven/org.springframework.cloud/spring-cloud-starter-netflix-hystrix/pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-starter-netflix</artifactId>
		<version>2.0.0.RELEASE</version>
	</parent>
	<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
	<name>Spring Cloud Starter Netflix Hystrix</name>
	<description>Spring Cloud Starter Netflix Hystrix</description>
	<url>https://projects.spring.io/spring-cloud</url>
	<organization>
		<name>Pivotal Software, Inc.</name>
		<url>https://www.spring.io</url>
	</organization>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-netflix-core</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-netflix-ribbon</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-archaius</artifactId>
		</dependency>
		<dependency>
			<groupId>com.netflix.hystrix</groupId>
			<artifactId>hystrix-core</artifactId>
		</dependency>
		<dependency>
			<groupId>com.netflix.hystrix</groupId>
			<artifactId>hystrix-serialization</artifactId>
		</dependency>
		<dependency>
			<groupId>com.netflix.hystrix</groupId>
			<artifactId>hystrix-metrics-event-stream</artifactId>
		</dependency>
		<dependency>
			<groupId>com.netflix.hystrix</groupId>
			<artifactId>hystrix-javanica</artifactId>
		</dependency>
		<dependency>
			<groupId>io.reactivex</groupId>
			<artifactId>rxjava-reactive-streams</artifactId>
		</dependency>
	</dependencies>
</project>

這裏要講的HystrixCommands在spring-cloud-netflix-core這個組件裏

HystrixCommands

spring-cloud-netflix-core-2.0.0.RELEASE-sources.jar!/org/springframework/cloud/netflix/hystrix/HystrixCommands.java

/**
 * Utility class to wrap a {@see Publisher} in a {@see HystrixObservableCommand}. Good for
 * use in a Spring WebFlux application. Allows more flexibility than the @HystrixCommand
 * annotation.
 * @author Spencer Gibb
 */
public class HystrixCommands {

	public static <T> PublisherBuilder<T> from(Publisher<T> publisher) {
		return new PublisherBuilder<>(publisher);
	}

	public static class PublisherBuilder<T> {
		private final Publisher<T> publisher;
		private String commandName;
		private String groupName;
		private Publisher<T> fallback;
		private Setter setter;
		private HystrixCommandProperties.Setter commandProperties;
		private boolean eager = false;
		private Function<HystrixObservableCommand<T>, Observable<T>> toObservable;

		public PublisherBuilder(Publisher<T> publisher) {
			this.publisher = publisher;
		}

		public PublisherBuilder<T> commandName(String commandName) {
			this.commandName = commandName;
			return this;
		}

		public PublisherBuilder<T> groupName(String groupName) {
			this.groupName = groupName;
			return this;
		}

		public PublisherBuilder<T> fallback(Publisher<T> fallback) {
			this.fallback = fallback;
			return this;
		}

		public PublisherBuilder<T> setter(Setter setter) {
			this.setter = setter;
			return this;
		}

		public PublisherBuilder<T> commandProperties(
				HystrixCommandProperties.Setter commandProperties) {
			this.commandProperties = commandProperties;
			return this;
		}

		public PublisherBuilder<T> commandProperties(
				Function<HystrixCommandProperties.Setter, HystrixCommandProperties.Setter> commandProperties) {
			if (commandProperties == null) {
				throw new IllegalArgumentException(
						"commandProperties must not both be null");
			}
			return this.commandProperties(
					commandProperties.apply(HystrixCommandProperties.Setter()));
		}

		public PublisherBuilder<T> eager() {
			this.eager = true;
			return this;
		}

		public PublisherBuilder<T> toObservable(Function<HystrixObservableCommand<T>, Observable<T>> toObservable) {
			this.toObservable = toObservable;
			return this;
		}

		public Publisher<T> build() {
			if (!StringUtils.hasText(commandName) && setter == null) {
				throw new IllegalStateException("commandName and setter can not both be empty");
			}
			Setter setterToUse = getSetter();

			PublisherHystrixCommand<T> command = new PublisherHystrixCommand<>(setterToUse, this.publisher, this.fallback);

			Observable<T> observable = getObservableFunction().apply(command);

			return RxReactiveStreams.toPublisher(observable);
		}

		public Function<HystrixObservableCommand<T>, Observable<T>> getObservableFunction() {
			Function<HystrixObservableCommand<T>, Observable<T>> observableFunc;

			if (this.toObservable != null) {
				observableFunc = this.toObservable;
			} else if (this.eager) {
				observableFunc = cmd -> cmd.observe();
			} else { // apply a default onBackpressureBuffer if not eager
				observableFunc = cmd -> cmd.toObservable().onBackpressureBuffer();
			}
			return observableFunc;
		}

		public Setter getSetter() {
			Setter setterToUse;
			if (this.setter != null) {
				setterToUse = this.setter;
			} else {
				String groupNameToUse;
				if (StringUtils.hasText(this.groupName)) {
					groupNameToUse = this.groupName;
				} else {
					groupNameToUse = commandName + "group";
				}

				HystrixCommandGroupKey groupKey = HystrixCommandGroupKey.Factory.asKey(groupNameToUse);
				HystrixCommandKey commandKey = HystrixCommandKey.Factory.asKey(this.commandName);
				HystrixCommandProperties.Setter commandProperties = this.commandProperties != null
						? this.commandProperties
						: HystrixCommandProperties.Setter();
				setterToUse = Setter.withGroupKey(groupKey).andCommandKey(commandKey)
						.andCommandPropertiesDefaults(commandProperties);
			}
			return setterToUse;
		}

		public Flux<T> toFlux() {
			return Flux.from(build());
		}

		public Mono<T> toMono() {
			return Mono.from(build());
		}

	}

	private static class PublisherHystrixCommand<T> extends HystrixObservableCommand<T> {

		private Publisher<T> publisher;
		private Publisher<T> fallback;

		protected PublisherHystrixCommand(Setter setter, Publisher<T> publisher,
				Publisher<T> fallback) {
			super(setter);
			this.publisher = publisher;
			this.fallback = fallback;
		}

		@Override
		protected Observable<T> construct() {
			return RxReactiveStreams.toObservable(publisher);
		}

		@Override
		protected Observable<T> resumeWithFallback() {
			if (this.fallback != null) {
				return RxReactiveStreams.toObservable(this.fallback);
			}
			return super.resumeWithFallback();
		}
	}
}

從類註釋能夠看到這個類就是爲了方便webflux應用使用hystrix而設計的。

實例

@Test
    public void testHystrixFallback() throws InterruptedException {
        Mono<String> delayMono = Mono.just("hello")
                .delayElement(Duration.ofMillis(500));
        Mono<String> result = HystrixCommands.from(delayMono)
                .commandName("demoCmd")
                .groupName("demoGroup")
                .eager()
                .commandProperties(HystrixCommandProperties.Setter()
                        .withExecutionIsolationStrategy(HystrixCommandProperties.ExecutionIsolationStrategy.THREAD)
                        .withExecutionTimeoutInMilliseconds(1000)
                )
                .fallback(Mono.just("from fallback"))
                .toMono();

        System.out.println(result.block());

    }

• HystrixCommands.from方法能夠對Publisher進行hystrix包裝
• commandName用於指定hystrix的command名稱
• groupName用於指定hystrix的group名稱
• eager是默認方式，表示使用的是observe()方法，至關於hot Observable，只能消費從訂閱時刻以後的數據，lazy使用的是toObservable()方法，至關於cold Observable，能夠消費訂閱以前的數據。
• commandProperties用於指定command的屬性，好比executionIsolationStrategy、executionTimeoutInMilliseconds
• fallback用於指定fallback的操做

另外配置文件也能夠指定默認的參數，好比

hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds : 6000
      circuitBreaker:
        sleepWindowInMilliseconds: 10000
      metrics:
        rollingStats:
          timeInMilliseconds : 18000

小結

HystrixCommands就是spring cloud對netflix hystrix的包裝，以方便webflux裏頭使用hystrix，就免得再去使用AOP技術了。

doc

• Reactive Execution
• hystrix-javanica
• visualizing-reactive-streams-hot-and-cold