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。但基本上每个服务都会有一个全局globalId，能够清除调用链路，可以有两种解决方案

解决方案一

可以在每次远程调用时，使用@RequestHeader注解重新封装请求头

    @GetMapping("/test")String test(String res, @RequestHeader String globalId);

解决方案二

可以使用springcloud提供的feign拦截器RequestInterceptor，拦截请求头重新进行封装

package com.test.feignheader.config;import feign.RequestInterceptor;
import feign.RequestTemplate;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;import javax.servlet.http.HttpServletRequest;/*** @Description: feign拦截器功能, 解决header丢失问题**/@Configuration
public class FeignConfig {@Bean("requestInterceptor")public RequestInterceptor requestInterceptor() {RequestInterceptor requestInterceptor = new RequestInterceptor() {@Overridepublic void apply(RequestTemplate template) {//1、使用RequestContextHolder拿到刚进来的请求数据ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();if (requestAttributes != null) {//老请求HttpServletRequest request = requestAttributes.getRequest();if (request != null) {//2、同步请求头的数据（主要是cookie）//把老请求的cookie值放到新请求上来，进行一个同步String cookie = request.getHeader("Cookie");template.header("Cookie", cookie);}}}};return requestInterceptor;}}

 也可以参考下面的代码进行封装

public class FeignBasicAuthRequestInterceptor implements RequestInterceptor {private static final Logger logger = LoggerFactory.getLogger(FeignBasicAuthRequestInterceptor.class);@Overridepublic 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);//跳过 content-length，避免追加参数导致content-length值与实际长度不一样if (name.equals("content-length")) {continue;}requestTemplate.header(name, values);}}/**  body一般不需要处理，否则会导致微服务调用异常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());}*/}
}

配置 让所有 FeignClient，使用 FeignBasicAuthRequestInterceptor

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

也可以配置让 某个 FeignClient 使用这个 FeignBasicAuthRequestInterceptor

feign:client:config:xxxx: # 远程服务名connectTimeout: 5000readTimeout: 5000loggerLevel: basicrequestInterceptors: 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。

自定义策略

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。

@Component
public 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.");}}@Overridepublic <T> Callable<T> wrapCallable(Callable<T> callable) {RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();return new WrappedCallable<>(callable, requestAttributes);}@Overridepublic 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);}@Overridepublic ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey,HystrixThreadPoolProperties threadPoolProperties) {return this.delegate.getThreadPool(threadPoolKey, threadPoolProperties);}@Overridepublic BlockingQueue<Runnable> getBlockingQueue(int maxQueueSize) {return this.delegate.getBlockingQueue(maxQueueSize);}@Overridepublic <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;}@Overridepublic 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 。