OpenFeign开启Hystrix时，实现服务间并且调用时传递header以及新增header, header透传

场景：web端调用A服务，A服务调用B服务
A服务将web端通过header中的token解析，获取到user信息，A调用B服务时需要将token或者用户信息传递给B服务
暴力解决的方案为：直接把user作为一个对象传递就可以了，但是这种做法导致每个接口都需要传递user对象，非常麻烦
我们的做法是将token或者user信息统一封装在feign的header中传递给B服务，如果没有开启hystrix，这种方式一点问题也没有，但是开启了hytrix后，出现了大问题！！

1.FeignInterceptor实现RequestInterceptor

package xxx.xxx.xxx;

import feign.RequestInterceptor;
import feign.RequestTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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;
import java.util.Enumeration;

@Configuration
public class FeignBasicAuthRequestInterceptor implements RequestInterceptor {


    private static final Logger log = 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);
                if(name.equals("Authorization")){
                    log.info(values);
                }
                requestTemplate.header(name, values);
            }
        }
    }

}
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我们定义一个FeignInterceptor实现RequestInterceptor，在通过feign调用的时候，会自动进入此拦截器，在此拦截器中，将token或者user信息放置到header中

2、重写HystrixConcurrencyStrategy

开启hystrix后，Hystrix内部提供了两种模式执行逻辑：信号量、线程池。但是，spring cloud官方是不推荐信号量这种方式的，我们只能采用线程池这种方式。

线程池这种方式，是开启了另外一个线程（线程隔离）来进行feign调用的，主线程中的request是传递不到新开启线程中的，所以，我们要重写HystrixConcurrencyStrategy(并发策略)

package xxx.xxx.xxx;

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.Configuration;
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;

/**
 * 重写并发策略
 *
 * @author xxx
 * @Date 2022/6/27
 **/
@Slf4j
@Configuration
public class FeignHystrixConcurrencyStrategy extends HystrixConcurrencyStrategy {

    private HystrixConcurrencyStrategy delegate;

    /**
     * 无参构造
     */
    public FeignHystrixConcurrencyStrategy() {
        try {
            this.delegate = HystrixPlugins.getInstance().getConcurrencyStrategy();
            if (this.delegate instanceof FeignHystrixConcurrencyStrategy) {
                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);
            //重置HystrixPlugins再重新填充 否则会报 Another strategy was already registered.
            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);
        }
    }

    /**
     * 日志记录
     * @param eventNotifier
     * @param metricsPublisher
     * @param propertiesStrategy
     */
    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;

        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();
            }
        }
    }


}

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测试：
场景：openfeign接口写在服务提供方即服务B中，服务A引入服务B的feign接口模块
1.在服务调用方即服务A配置这两个文件，可以实现header透传
2.在服务提供方即服务B配置这两个文件，可以实现header透传
3.服务调用方即服务A配置第二步，服务提供方配置第一步，也可以实现header透传
3.服务调用方即服务A配置第一步，服务提供方配置第二步，也可以实现header透传