Hystrix源码分析

Hystrix的源码需要有一定基础rxjava，所以接下来的源码分析会很简单，因为作者只是想了解下Hystrix整个流程，对rxjava不熟悉。

Hystrix源码

Feign已经整合了Hystrix，那里面是如何工作的呢？配置文件中feign.hystrix.enabled=true，那我们为什么需要这个配置呢？

首先我们看下FeignClientsConfiguration，这个文件加载的时候，里面的bean也会相应的加载到容器中，其中有一个Bean时Builder

@Configuration(
        proxyBeanMethods = false
    )
    @ConditionalOnClass({HystrixCommand.class, HystrixFeign.class})
    protected static class HystrixFeignConfiguration {
        protected HystrixFeignConfiguration() {
        }

        @Bean
        @Scope("prototype")
        @ConditionalOnMissingBean
        @ConditionalOnProperty(
            name = {"feign.hystrix.enabled"}
        )
        public Builder feignHystrixBuilder() {
            return HystrixFeign.builder();
        }
    }

开启了Hystrix，Builder的Bean类则会是HystrixFeign而就不是Feign了。有了HystrixFeign这个类，我们可以查到FeignAutoConfiguration类中

@Configuration(
        proxyBeanMethods = false
    )
    @ConditionalOnClass(
        name = {"feign.hystrix.HystrixFeign"}
    )
    protected static class HystrixFeignTargeterConfiguration {
        protected HystrixFeignTargeterConfiguration() {
        }

        @Bean
        @ConditionalOnMissingBean
        public Targeter feignTargeter() {
            return new HystrixTargeter();
        }
    }

生成HystrixTargeter类，调用FeignClientFactoryBean类中getObject的方法时，Builder和Target对象就是之前说的两个。

public  T target(FeignClientFactoryBean factory, Builder feign, FeignContext context, HardCodedTarget target) {
        if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
            return feign.target(target);
        } else {
            feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder)feign;
            String name = StringUtils.isEmpty(factory.getContextId()) ? factory.getName() : factory.getContextId();
            SetterFactory setterFactory = (SetterFactory)this.getOptional(name, context, SetterFactory.class);
            if (setterFactory != null) {
                builder.setterFactory(setterFactory);
            }

            Class fallback = factory.getFallback();
            if (fallback != Void.TYPE) {
                return this.targetWithFallback(name, context, target, builder, fallback);
            } else {
                Class fallbackFactory = factory.getFallbackFactory();
                return fallbackFactory != Void.TYPE ? this.targetWithFallbackFactory(name, context, target, builder, fallbackFactory) : feign.target(target);
            }
        }
    }

HystrixTargeter.target核心方法，先加载fallback，没有则加载fallbackFactory，这个可以说明fallback的优先级高。接下来查看targetwithFallback方法

Feign build(final FallbackFactory nullableFallbackFactory) {
            super.invocationHandlerFactory(new InvocationHandlerFactory() {
                public InvocationHandler create(Target target, Map dispatch) {
                    return new HystrixInvocationHandler(target, dispatch, Builder.this.setterFactory, nullableFallbackFactory);
                }
            });
            super.contract(new HystrixDelegatingContract(this.contract));
            return super.build();
        }

生成HystrixInvocationHandler实例，并且执行父类的build().

public Feign build() {
            Factory synchronousMethodHandlerFactory = new Factory(this.client, this.retryer, this.requestInterceptors, this.logger, this.logLevel, this.decode404, this.closeAfterDecode, this.propagationPolicy);
            ParseHandlersByName handlersByName = new ParseHandlersByName(this.contract, this.options, this.encoder, this.decoder, this.queryMapEncoder, this.errorDecoder, synchronousMethodHandlerFactory);
            return new ReflectiveFeign(handlersByName, this.invocationHandlerFactory, this.queryMapEncoder);
        }

赋值，生成ReflectiveFeign执行其newInstance方法。接下来和Fiegn流程差不多，但是需要注意的是，调用提供者的时候HystrixInvocationHandler会先拦截其动作，调用其invoke方法

public Object invoke(Object proxy, final Method method, final Object[] args) throws Throwable {
        if (!"equals".equals(method.getName())) {
            if ("hashCode".equals(method.getName())) {
                return this.hashCode();
            } else if ("toString".equals(method.getName())) {
                return this.toString();
            } else {
                HystrixCommand