• 添加熔断依赖

   <dependency>
     <groupId>org.springframework.cloud</groupId>
     <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
   </dependency>
  

• application.yml 配置熔断

  #------feign配置---------
  feign:
    client:
      config:
        default:
      connectTimeout: 5000 #feign 远程连接超时时间 5s
      readTimeout: 10000 #feign 远程获取数据超时时间 10s
      loggerLevel: basic
    hystrix:
      enabled: true # 启用熔断
  #------------hystrix 熔断配置-------------------
  hystrix:
    command:
      default:
        execution:
      timeout:
        enabled: true
      isolation:
        thread:
          timeoutInMilliseconds: 20000 #超时多长时间，熔断 20s
  
  注意：1.通常熔断的超时时间需要配置的比ReadTimeout长,ReadTimeout比ConnectTimeout长,否则还未重试,就熔断了;
        2.为了确保重试机制的正常运作,理论上（以实际情况为准）建议hystrix的超时时间为:(1 + MaxAutoRetries + MaxAutoRetriesNextServer) * ReadTimeout;
  

• 开启熔断后，不能获取ThreadLocal 中的设置的值解决方法：

  • 如：获取当前的 HttpServletRequest  为null

    public static HttpServletRequest getRequest() { RequestAttributes requestAttributes = RequestContextHolder.currentRequestAttributes(); return (requestAttributes == null) ? null : ((ServletRequestAttributes) requestAttributes).getRequest(); }

    解决方法一：

调整隔离策略：
hystrix.command.default.execution.isolation.strategy: SEMAPHORE

但该方案不是特别好。原因是Hystrix官方强烈建议使用THREAD作为隔离策略！

    解决方法二： 自定义熔断的并发策略（可参考：https://www.jianshu.com/p/f30892335057）：

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 org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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;

/**
 * 熔断并发策略
 */
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) {
                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 var5) {
            log.error("Failed to register Sleuth Hystrix Concurrency Strategy", var5);
        }

    }

    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.");
        }

    }

    public <T> Callable<T> wrapCallable(Callable<T> callable) {
        RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
        return new FeignHystrixConcurrencyStrategy.WrappedCallable(callable, requestAttributes);
    }

    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);
    }

    public ThreadPoolExecutor getThreadPool(HystrixThreadPoolKey threadPoolKey, HystrixThreadPoolProperties threadPoolProperties) {
        return this.delegate.getThreadPool(threadPoolKey, threadPoolProperties);
    }

    public BlockingQueue<Runnable> getBlockingQueue(int maxQueueSize) {
        return this.delegate.getBlockingQueue(maxQueueSize);
    }

    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;
        }

        public T call() throws Exception {
            try {
                RequestContextHolder.setRequestAttributes(this.requestAttributes);
                return target.call();
            } finally {
                RequestContextHolder.resetRequestAttributes();
            }
        }
    }
}

  Feign 请求微服务请求头添加Token：

import com.weaf.onet.utils.WebUtil;
import feign.RequestInterceptor;
import feign.RequestTemplate;

/**
 * Feign请求拦截器（调用微服务层）
 **/
 class FeignAuthRequestInterceptor implements RequestInterceptor {

    @Override
    public void apply(RequestTemplate template) {
        Integer tenantId= WebUtil.getTenantId();
        template.header("tenantId", String.valueOf(tenantId));
    }

}

配置 Feign ：

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;


@Configuration
public class FeignConfiguration {

    /**
     * 创建Feign请求拦截器，在发送请求前设置认证的token,各个微服务将token设置到环境变量中来达到通用
     * @return
     */
    @Bean
    public FeignAuthRequestInterceptor authRequestInterceptor() {
        return new FeignAuthRequestInterceptor();
    }

    // 配置熔断策略
    @Bean
    public FeignHystrixConcurrencyStrategy feignHystrixConcurrencyStrategy() {
        return new FeignHystrixConcurrencyStrategy();
    }
}