FeignClient 一直走 fallbackFactory 导致 RequestContextHolder.getRequestAttributes() 为空

故事

tmd，就这个问题搞了我一天，还是太年轻，最近一直在加班也没得时间写博客，但是就这个问题，必须要记录一下

场景复现

系统采用微服务形式，采用 FeignClient 进行远程调用，其中加入了 Hystrix 进行熔断降级处理，然后发现一直使用 FeignClient 指定的服务名后，请求一直都在走 fallbackFactory，觉得可能是由于没带 token 的原因，所以无法请求，然后配置了 configuration，不配不知道，一配吓一跳

问题

配置 configuration,发现 attributes 为空。

@Configuration
public class FeignConfig implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate requestTemplate) {
        ServletRequestAttributes attributes = (ServletRequestAttributes)RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = attributes.getRequest();
        //添加token
        requestTemplate.header("Access-Token", request.getHeader("Access-Token"));
    }
}

然后又开始一阵捣鼓，最后发现，是因为加入熔断降级导致的，由于加入熔断降级导致的

Hystrix 的默认隔离策略是 THREAD 。而 RequestContextHolder 源码中，使用了两个血淋淋的 ThreadLocal

所以导致前后的是不同的线程。

解决办法

自定义 HystrixConcurrencyStrategy，具体实现如下

import com.netflix.hystrix.HystrixThreadPoolKey;
import com.netflix.hystrix.HystrixThreadPoolProperties;
import com.netflix.hystrix.strategy.HystrixPlugins;
import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategy;
import com.netflix.hystrix.strategy.concurrency.HystrixRequestVariable;
import com.netflix.hystrix.strategy.concurrency.HystrixRequestVariableLifecycle;
import com.netflix.hystrix.strategy.eventnotifier.HystrixEventNotifier;
import com.netflix.hystrix.strategy.executionhook.HystrixCommandExecutionHook;
import com.netflix.hystrix.strategy.metrics.HystrixMetricsPublisher;
import com.netflix.hystrix.strategy.properties.HystrixPropertiesStrategy;
import com.netflix.hystrix.strategy.properties.HystrixProperty;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;
import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.context.request.RequestContextHolder;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * <p>
 *     Feign远程调用设置configuration后，RequestContextHolder.getRequestAttributes()为空的问题
 *     由于getRequestAttributes为空无法设置远调的token，导致一直都在走fallBackFactory
 *     出现问题原因是因为加入了服务降级，hystrix
 * </p>
 *
 * @author sirwsl
 */
@Component
@Primary
@Slf4j
public class CustomFeignHystrixConcurrencyStrategy extends HystrixConcurrencyStrategy {

    private HystrixConcurrencyStrategy hystrixConcurrencyStrategy;

    public CustomFeignHystrixConcurrencyStrategy() {
        try {
            this.hystrixConcurrencyStrategy = HystrixPlugins.getInstance().getConcurrencyStrategy();
            if (this.hystrixConcurrencyStrategy instanceof CustomFeignHystrixConcurrencyStrategy) {
                // Welcome to singleton hell...
                return;
            }
            HystrixCommandExecutionHook commandExecutionHook =
                    HystrixPlugins.getInstance().getCommandExecutionHook();
            HystrixEventNotifier eventNotifier = HystrixPlugins.getInstance().getEventNotifier();
            HystrixMetricsPublisher metricsPublisher = HystrixPlugins.getInstance().getMetricsPublisher();
            HystrixPropertiesStrategy propertiesStrategy =
                    HystrixPlugins.getInstance().getPropertiesStrategy();
            this.logCurrentStateOfHystrixPlugins(eventNotifier, metricsPublisher, propertiesStrategy);
            HystrixPlugins.reset();
            HystrixPlugins.getInstance().registerConcurrencyStrategy(this);
            HystrixPlugins.getInstance().registerCommandExecutionHook(commandExecutionHook);
            HystrixPlugins.getInstance().registerEventNotifier(eventNotifier);
            HystrixPlugins.getInstance().registerMetricsPublisher(metricsPublisher);
            HystrixPlugins.getInstance().registerPropertiesStrategy(propertiesStrategy);
        } catch (Exception e) {
            log.error("Failed to register Sleuth Hystrix Concurrency Strategy", e);
        }
    }

    private void logCurrentStateOfHystrixPlugins(HystrixEventNotifier eventNotifier,
                                                 HystrixMetricsPublisher metricsPublisher, HystrixPropertiesStrategy propertiesStrategy) {
        if (log.isDebugEnabled()) {
            log.debug("Current Hystrix plugins configuration is [" + "concurrencyStrategy ["
                    + this.hystrixConcurrencyStrategy + "]," + "eventNotifier [" + eventNotifier + "]," + "metricPublisher ["
                    + metricsPublisher + "]," + "propertiesStrategy [" + propertiesStrategy + "]," + "]");
            log.debug("Registering Sleuth Hystrix Concurrency Strategy.");
        }
    }

    @Override
    public <T> Callable<T> wrapCallable(Callable<T> callable) {
        RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
        return new WrappedCallable<>(callable, requestAttributes);
    }

    @Override
    public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,
                                            HystrixProperty<Integer> corePoolSize, HystrixProperty<Integer> maximumPoolSize,
                                            HystrixProperty<Integer> keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        return this.hystrixConcurrencyStrategy.getThreadPool(threadPoolKey, corePoolSize, maximumPoolSize, keepAliveTime,
                unit, workQueue);
    }

    @Override
    public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,
                                            HystrixThreadPoolProperties threadPoolProperties) {
        return this.hystrixConcurrencyStrategy.getThreadPool(threadPoolKey, threadPoolProperties);
    }

    @Override
    public BlockingQueue<Runnable> getBlockingQueue(int maxQueueSize) {
        return this.hystrixConcurrencyStrategy.getBlockingQueue(maxQueueSize);
    }

    @Override
    public <T> HystrixRequestVariable<T> getRequestVariable(HystrixRequestVariableLifecycle<T> rv) {
        return this.hystrixConcurrencyStrategy.getRequestVariable(rv);
    }

    static class WrappedCallable<T> implements Callable<T> {
        private final Callable<T> target;
        private final RequestAttributes requestAttributes;

        public WrappedCallable(Callable<T> target, RequestAttributes requestAttributes) {
            this.target = target;
            this.requestAttributes = requestAttributes;
        }

        @Override
        public T call() throws Exception {
            try {
                RequestContextHolder.setRequestAttributes(requestAttributes);
                return target.call();
            } finally {
                RequestContextHolder.resetRequestAttributes();
            }
        }
    }

}

参考地址

实用技巧：Hystrix 传播 ThreadLocal 对象（两种方案） | 周立的博客 - 关注 Spring Cloud、Docker (itmuch.com)