Hystrix支持ThreadLocal设置传递

Hystrix使用命令模式将所有对外部服务的调用包装在HystrixCommand或HystrixObservableCommand对象中，并将该对象放在单独的线程中执行。因为调用在单独的线程中执行，因此原线程的ThreadLocal设置就失效了。

因此，为了将当前线程的ThreadLocal数值传递至Hystrix的线程中，可以参考下文。

封装Callable任务

public final class DelegatingUserContextCallable<V> implements Callable<V> {
    private final Callable<V> delegate;
    // 用户信息上下文（根据项目实际情况定义ThreadLocal上下文）
    private UserContext originalUserContext;

    public DelegatingUserContextCallable(Callable<V> delegate,
                                         UserContext userContext) {
        this.delegate = delegate;
        this.originalUserContext = userContext;
    }

    public V call() throws Exception {
        // 将当前的用户上下文设置进Hystrix线程的TreadLocal中
        UserContextHolder.setContext(originalUserContext);
        try {
            return delegate.call();
        }
        finally {
            // 执行完毕，记得清理ThreadLocal资源
            this.originalUserContext = null;
        }
    }

    public static <V> Callable<V> create(Callable<V> delegate,
                                         UserContext userContext) {
        return new DelegatingUserContextCallable<V>(delegate, userContext);
    }
}

实现Hystrix的并发策略类

public class ThreadLocalAwareStrategy extends HystrixConcurrencyStrategy {
    
    // 最简单的方式就是引入现有的并发策略，进行功能扩展
    private final HystrixConcurrencyStrategy existingConcurrencyStrategy;

    public ThreadLocalAwareStrategy(
            HystrixConcurrencyStrategy existingConcurrencyStrategy) {
        this.existingConcurrencyStrategy = existingConcurrencyStrategy;
    }

    @Override
    public BlockingQueue<Runnable> getBlockingQueue(int maxQueueSize) {
        return existingConcurrencyStrategy != null
                ? existingConcurrencyStrategy.getBlockingQueue(maxQueueSize)
                : super.getBlockingQueue(maxQueueSize);
    }

    @Override
    public <T> HystrixRequestVariable<T> getRequestVariable(
            HystrixRequestVariableLifecycle<T> rv) {
        return existingConcurrencyStrategy != null
                ? existingConcurrencyStrategy.getRequestVariable(rv)
                : super.getRequestVariable(rv);
    }

    @Override
    public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,
                                            HystrixProperty<Integer> corePoolSize,
                                            HystrixProperty<Integer> maximumPoolSize,
                                            HystrixProperty<Integer> keepAliveTime, TimeUnit unit,
                                            BlockingQueue<Runnable> workQueue) {
        return existingConcurrencyStrategy != null
                ? existingConcurrencyStrategy.getThreadPool(threadPoolKey, corePoolSize,
                maximumPoolSize, keepAliveTime, unit, workQueue)
                : super.getThreadPool(threadPoolKey, corePoolSize, maximumPoolSize,
                keepAliveTime, unit, workQueue);
    }

    @Override
    public <T> Callable<T> wrapCallable(Callable<T> callable) {
        return existingConcurrencyStrategy != null
                ? existingConcurrencyStrategy
                .wrapCallable(new DelegatingUserContextCallable<>(callable, UserContextHolder.getContext()))
                : super.wrapCallable(new DelegatingUserContextCallable<T>(callable, UserContextHolder.getContext()));
    }
}

Hystrix注入新并发策略并进行刷新

@Configuration
public class ThreadLocalConfiguration {

    @Autowired(required = false)
    private HystrixConcurrencyStrategy existingConcurrencyStrategy;

    @PostConstruct
    public void init() {
        // Keeps references of existing Hystrix plugins.
        HystrixEventNotifier eventNotifier = HystrixPlugins.getInstance()
                .getEventNotifier();
        HystrixMetricsPublisher metricsPublisher = HystrixPlugins.getInstance()
                .getMetricsPublisher();
        HystrixPropertiesStrategy propertiesStrategy = HystrixPlugins.getInstance()
                .getPropertiesStrategy();
        HystrixCommandExecutionHook commandExecutionHook = HystrixPlugins.getInstance()
                .getCommandExecutionHook();

        HystrixPlugins.reset();

        HystrixPlugins.getInstance().registerConcurrencyStrategy(new ThreadLocalAwareStrategy(existingConcurrencyStrategy));
        HystrixPlugins.getInstance().registerEventNotifier(eventNotifier);
        HystrixPlugins.getInstance().registerMetricsPublisher(metricsPublisher);
        HystrixPlugins.getInstance().registerPropertiesStrategy(propertiesStrategy);
        HystrixPlugins.getInstance().registerCommandExecutionHook(commandExecutionHook);
    }
}

添加拦截器

Hystrix经常与OpenFeign搭配使用，此时如果想利用到ThreadLocal中变量，可以给OpenFeign实例添加拦截器，具体代码可自行搜索。