HystrixPlugins

　　獲取並發相關類（HystrixConcurrencyStrategy）、事件通知類（HystrixEventNotifier）、度量信息類（HystrixMetricsPublisher）、Properties配置類（HystrixPropertiesStrategy）、HystrixCommand回調函數類（HystrixCommandExecutionHook）5類插件。

　　以HystrixEventNotifier為例，HystrixPlugins 首先會去properties（HystrixDynamicProperties）配置下需找相應類型的實現類。

private static <T> T getPluginImplementationViaProperties(Class<T> pluginClass, HystrixDynamicProperties dynamicProperties) {
        String classSimpleName = pluginClass.getSimpleName();
        // Check Archaius for plugin class.
        String propertyName = "hystrix.plugin." + classSimpleName + ".implementation";
        String implementingClass 
 
= dynamicProperties.getString(propertyName, null).get();

　　如果返回null，則通過ServiceLoader獲取相應類型的實現類。

private <T> T getPluginImplementation(Class<T> pluginClass) {
        T p = getPluginImplementationViaProperties(pluginClass, dynamicProperties);
        if (p != null) return p;        
        
 
return findService(pluginClass, classLoader);
    }
    private static <T> T findService(
            Class<T> spi, 
            ClassLoader classLoader) throws ServiceConfigurationError {
        
        ServiceLoader<T> sl = ServiceLoader.load(spi,
                classLoader);
        for (T s : sl) {
            if (s != null)
                return s;
        }
        return null;
    }

　　如果獲取成功，存儲變量中，其他四個組件實現原理一樣

final AtomicReference<HystrixEventNotifier> notifier = new AtomicReference<HystrixEventNotifier>();
public HystrixEventNotifier getEventNotifier() {
        if (notifier.get() == null) {
            // check for an implementation from Archaius first
            Object impl = getPluginImplementation(HystrixEventNotifier.class);
            if (impl == null) {
                // nothing set via Archaius so initialize with default
                notifier.compareAndSet(null, HystrixEventNotifierDefault.getInstance());
                // we don‘t return from here but call get() again in case of thread-race so the winner will always get returned
            } else {
                // we received an implementation from Archaius so use it
                notifier.compareAndSet(null, (HystrixEventNotifier) impl);
            }
        }
        return notifier.get();
    }

　　獲取HystrixDynamicProperties對象，流程與獲取插架類似，只是通過HystrixDynamicPropertiesSystemProperties配置下需找相應類型的實現類。

private static HystrixDynamicProperties resolveDynamicProperties(ClassLoader classLoader, LoggerSupplier logSupplier) {
        HystrixDynamicProperties hp = getPluginImplementationViaProperties(HystrixDynamicProperties.class, 
                HystrixDynamicPropertiesSystemProperties.getInstance());
        if (hp != null) {
            logSupplier.getLogger().debug(
                    "Created HystrixDynamicProperties instance from System property named "
                    + "\"hystrix.plugin.HystrixDynamicProperties.implementation\". Using class: {}", 
                    hp.getClass().getCanonicalName());
            return hp;
        }
        hp = findService(HystrixDynamicProperties.class, classLoader);
        if (hp != null) {
            logSupplier.getLogger()
                    .debug("Created HystrixDynamicProperties instance by loading from ServiceLoader. Using class: {}", 
                            hp.getClass().getCanonicalName());
            return hp;
        }
        hp = HystrixArchaiusHelper.createArchaiusDynamicProperties();
        if (hp != null) {
            logSupplier.getLogger().debug("Created HystrixDynamicProperties. Using class : {}", 
                    hp.getClass().getCanonicalName());
            return hp;
        }
        hp = HystrixDynamicPropertiesSystemProperties.getInstance();
        logSupplier.getLogger().info("Using System Properties for HystrixDynamicProperties! Using class: {}", 
                hp.getClass().getCanonicalName());
        return hp;
    }

hystrix源碼之插架