Spring cloud 在跨服务调用（feign）时 开启熔断器 （hystrix）获取当前请求头 信息

在 spring cloud 中 使用 feign 进行跨服务调用时 有的时候 需要获取当前模块的 请求头里的参数 传输到另一个模块 使用

例如：token 一般放在 请求头中

用户从前端把token 发给 A模块 然后 A模块 调用 B 模块时 需要带着这个token 传输到 B模块

在不开启 熔断器的情况 使用 ServletRequestAttributes 这个类获取请求头参数 完全没问题

   public static HttpServletRequest getHttpServletRequest() throws AuthException {
        return ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
    }

但是 如果开启 熔断器（hystrix）后 这个对象 就会出现 空指针异常 找不到这个对象

就需要 重写 HystrixConcurrencyStrategy 这个类 来实现

package com.erp.init.config.filter;

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.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;

/**
 * User: Json
 * <p>
 * Date: 2022/3/11
 **/
@Slf4j
@Component
public class RequestAttributeHystrixConcurrencyStrategy extends HystrixConcurrencyStrategy {
 //   private static final Log log = LogFactory.getLog(RequestAttributeHystrixConcurrencyStrategy.class);

    private HystrixConcurrencyStrategy delegate;

    public RequestAttributeHystrixConcurrencyStrategy() {
        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 <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();
            }
        }
    }
}

重启 项目后 即可获取 请求头的参数

**

原理：

jsonll.blog.csdn.net/article/det…