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在 Spring Cloud 中 微服务之间的调用会用到Feign，但是在默认情况下，Feign 调用远程服务存在Header请求头丢失问题。

首先需要写一个 Feign请求拦截器，通过实现RequestInterceptor接口,完成对所有的Feign请求,传递请求头和请求参数。

public class FeignBasicAuthRequestInterceptor implements RequestInterceptor { private static final Logger logger = LoggerFactory.getLogger(FeignBasicAuthRequestInterceptor.class); @Override public void apply(RequestTemplate requestTemplate) { ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder .getRequestAttributes(); HttpServletRequest request = attributes.getRequest(); Enumeration<String> headerNames = request.getHeaderNames(); if (headerNames != null) { while (headerNames.hasMoreElements()) { String name = headerNames.nextElement(); String values = request.getHeader(name); requestTemplate.header(name, values); } } Enumeration<String> bodyNames = request.getParameterNames(); StringBuffer body =new StringBuffer(); if (bodyNames != null) { while (bodyNames.hasMoreElements()) { String name = bodyNames.nextElement(); String values = request.getParameter(name); body.append(name).append("=").append(values).append("&"); } } if(body.length()!=0) { body.deleteCharAt(body.length()-1); requestTemplate.body(body.toString()); logger.info("feign interceptor body:{}",body.toString()); } }}

通过配置文件配置 让 所有 FeignClient，来使用 FeignBasicAuthRequestInterceptor

feign: client: config: default: connectTimeout: 5000 readTimeout: 5000 loggerLevel: basic requestInterceptors: com.leparts.config.FeignBasicAuthRequestInterceptor

也可以配置让 某个 FeignClient 来使用这个 FeignBasicAuthRequestInterceptor

feign: client: config: xxxx: # 远程服务名 connectTimeout: 5000 readTimeout: 5000 loggerLevel: basic requestInterceptors: com.leparts.config.FeignBasicAuthRequestInterceptor

经过测试，上面的解决方案可以正常的使用；但是出现了新的问题。

在转发Feign的请求头的时候, 如果开启了Hystrix, Hystrix的默认隔离策略是Thread(线程隔离策略), 因此转发拦截器内是无法获取到请求的请求头信息的。

可以修改默认隔离策略为信号量模式：

hystrix.command.default.execution.isolation.strategy=SEMAPHORE

但信号量模式不是官方推荐的隔离策略;另一个解决方法就是自定义Hystrix的隔离策略。

HystrixConcurrencyStrategy 是提供给开发者去自定义hystrix内部线程池及其队列，还提供了包装callable的方法，以及传递上下文变量的方法。所以可以继承了HystrixConcurrencyStrategy，用来实现了自己的并发策略。

@Componentpublic class FeignHystrixConcurrencyStrategy extends HystrixConcurrencyStrategy { private static final Logger log = LoggerFactory.getLogger(FeignHystrixConcurrencyStrategy.class); private HystrixConcurrencyStrategy delegate; public FeignHystrixConcurrencyStrategy() { try { this.delegate = HystrixPlugins.getInstance().getConcurrencyStrategy(); if (this.delegate instanceof FeignHystrixConcurrencyStrategy) { // 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 instance = HystrixPlugins.getInstance(); instance.registerConcurrencyStrategy(this); instance.registerCommandExecutionHook(commandExecutionHook); instance.registerEventNotifier(eventNotifier); instance.registerMetricsPublisher(metricsPublisher); instance.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 <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.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<Runnable> getBlockingQueue(int maxQueueSize) { return this.delegate.getBlockingQueue(maxQueueSize); } @Override public <T> HystrixRequestVariable<T> getRequestVariable(HystrixRequestVariableLifecycle<T> rv) { return this.delegate.getRequestVariable(rv); } static class WrappedCallable<T> implements Callable<T> { private final Callable<T> target; private final RequestAttributes requestAttributes; 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(); } } }}

致此，Feign调用丢失请求头的问题就解决的了 。

https://blog.csdn.net/zl1zl2zl3/article/details/79084368
https://cloud.spring.io/spring-cloud-static/spring-cloud-openfeign/2.2.0.RC2/reference/html/