FeignClient+Hystrix发起无法获取ServletRequest-经验总结

原因：feignclient转发会新启动一个线程，由于Hystrix隔离级别为线程级，context无法传递导致。

解决方案：

1，Hystrix隔离级别改为SEMAPHORE（信号量隔离策略）（官方不推荐） ->:

         execution.isolation.strategy:THREAD(SEMAPHORE)

        线程隔离策略涉及创建新线程，线程上下文切换，执行性能是低于信号量策略的。但是线程隔离策略完全隔离了依赖服务对当前的请求的影响，线程出现异常时不影响服务和其他请求，独立线程并发性高。线程隔离无法获取HTTPheader

        确保调用服务没有超时风险，可以考虑选择信号量隔离策略。

2，使用requestheader标签传递必须的header(适合少量) ->: 调用方和接收方接口需要明确参数

3，自定义Hystrix隔离隔离策略代码，将需要请求头放置于threadlocal中。（代码学习地址：feign 序列化_Spring Cloud(Feign+Hystrix)微服务之间参数传递-优快云博客）->:

public class RequestAttributeHystrixConcurrencyStrategy extends HystrixConcurrencyStrategy {

private static final Log log = LogFactory

.getLog(RequestAttributeHystrixConcurrencyStrategy.class);

private HystrixConcurrencyStrategy delegate;

public RequestAttributeHystrixConcurrencyStrategy() {

log.info("注入 Hystrix 熔断策略");

try {

this.delegate = HystrixPlugins.getInstance().getConcurrencyStrategy();

if (this.delegate instanceof RequestAttributeHystrixConcurrencyStrategy) {

// 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.delegate + "]," + "eventNotifier ["

+ eventNotifier + "]," + "metricPublisher [" + metricsPublisher + "],"

+ "propertiesStrategy [" + propertiesStrategy + "]," + "]");

log.debug("Registering Sleuth Hystrix Concurrency Strategy.");

}

}

@Override

public Callable wrapCallable(Callable callable) {

RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();

return new WrappedCallable<>(callable, requestAttributes);

}

@Override

public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,

HystrixProperty corePoolSize,

HystrixProperty maximumPoolSize,

HystrixProperty keepAliveTime, TimeUnit unit,

BlockingQueue workQueue) {

return this.delegate.getThreadPool(threadPoolKey, corePoolSize, maximumPoolSize,

keepAliveTime, unit, workQueue);

}

@Override

public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,

HystrixThreadPoolProperties threadPoolProperties) {

return this.delegate.getThreadPool(threadPoolKey, threadPoolProperties);

}

@Override

public BlockingQueue getBlockingQueue(int maxQueueSize) {

return this.delegate.getBlockingQueue(maxQueueSize);

}

@Override

public HystrixRequestVariable getRequestVariable(

HystrixRequestVariableLifecycle rv) {

return this.delegate.getRequestVariable(rv);

}

static class WrappedCallable implements Callable {

private final Callable target;

private final RequestAttributes requestAttributes;

public WrappedCallable(Callable 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();

}

}

}

}