Feign转发请求头，(防止session失效)

Feign自动转发HTTP请求头，(防止session失效)

微服务开发中经常有这样的需求，公司自定义了通用的请求头，需要在微服务的调用链中转发，比如在请求头中加入了token，或者某个自定义的信息uniqueId，总之就是自定义的一个键值对的东东，A服务调用B服务，B服务调用C服务，这样通用的东西如何让他在一个调用链中不断地传递下去呢？以A服务为例：

方案1

• 最傻的办法，在程序中获取，调用B的时候再转发，怎么获取在Controller中国通过注解获取，或者通过request对象获取，这个不难，在请求B服务的时候，通过注解将值放进去即可；简代码如下：

获取：
@RequestMapping(value = "/api/test", method = RequestMethod.GET)
public String testFun(@RequestParam String name, @RequestHeader("uniqueId") String uniqueId) {
    if(uniqueId == null ){
         return "Must defined the uniqueId , it can not be null";
    }
    log.info(uniqueId, "begin testFun... ");
 return uniqueId;
}

然后A使用Feign调用B服务的时候，传过去：

@FeignClient(value = "DEMO-SERVICE")
public interface CallClient {

   /**
 * 访问DEMO-SERVICE服务的/api/test接口，通过注解将logId传递给下游服务
  */
 @RequestMapping(value = "/api/test", method = RequestMethod.GET)
    String callApiTest(@RequestParam(value = "name") String name, @RequestHeader(value = "uniqueId") String uniqueId);

}

方案弊端：毫无疑问，这方案不好，因为对代码有侵入，需要开发人员没次手动的获取和添加，因此舍弃

方案2

• 服务通过请求拦截器，在请求从A发送到B之后，在拦截器内将自己需要的东东加到请求头：

 import com.intellif.log.LoggerUtilI;
import feign.RequestInterceptor;
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;
import java.util.Enumeration;

/**
 * 自定义的请求头处理类，处理服务发送时的请求头；
 * 将服务接收到的请求头中的uniqueId和token字段取出来，并设置到新的请求头里面去转发给下游服务
 * 比如A服务收到一个请求，请求头里面包含uniqueId和token字段，A处理时会使用Feign客户端调用B服务
 * 那么uniqueId和token这两个字段就会添加到请求头中一并发给B服务；
 *
 * @author mozping
 * @version 1.0
 * @date 2018/6/27 14:13
 * @see FeignHeadConfiguration
 * @since JDK1.8
 */
@Configuration
public class FeignHeadConfiguration {
    private final LoggerUtilI logger = LoggerUtilI.getLogger(this.getClass().getName());

    @Bean
    public RequestInterceptor requestInterceptor() {
        return requestTemplate -> {
            ServletRequestAttributes attrs = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
            if (attrs != null) {
                HttpServletRequest request = attrs.getRequest();
                Enumeration<String> headerNames = request.getHeaderNames();
                if (headerNames != null) {
                    while (headerNames.hasMoreElements()) {
                        String name = headerNames.nextElement();
                        String value = request.getHeader(name);
                        /**
                         * 遍历请求头里面的属性字段，将logId和token添加到新的请求头中转发到下游服务
                         * */
                        if ("uniqueId".equalsIgnoreCase(name) || "token".equalsIgnoreCase(name)) {
                            logger.debug("添加自定义请求头key:" + name + ",value:" + value);
                            requestTemplate.header(name, value);
                        } else {
                            logger.debug("FeignHeadConfiguration", "非自定义请求头key:" + name + ",value:" + value + "不需要添加!");
                        }
                    }
                } else {
                    logger.warn("FeignHeadConfiguration", "获取请求头失败！");
                }
            }
        };
    }

}

网上很多关于这种方法的博文或者资料，大同小异，但是有一个问题，在开启熔断器之后，这里的attrs就是null，因为熔断器默认的隔离策略是thread，也就是线程隔离，实际上接收到的对象和这个在发送给B不是一个线程，怎么办？有一个办法，修改隔离策略hystrix.command.default.execution.isolation.strategy=SEMAPHORE，改为信号量的隔离模式，但是不推荐，因为thread是默认的，而且要命的是信号量模式，熔断器不生效，比如设置了熔断时间hystrix.command.default.execution.isolation.semaphore.timeoutInMilliseconds=5000，五秒，如果B服务里面sleep了10秒，非得等到B执行完毕再返回，因此这个方案也不可取；但是有什么办法可以在默认的Thread模式下让拦截器拿到上游服务的请求头？自定义策略：代码如下：

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.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;

/**
 * 自定义Feign的隔离策略;
 * 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，这样的话转发线程和请求线程实际上是一个线程，这并不是最好的解决方法，信号量模式也不是官方最为推荐的隔离策略；另一个解决方法就是自定义Hystrix的隔离策略，思路是将现有的并发策略作为新并发策略的成员变量,在新并发策略中，返回现有并发策略的线程池、Queue；将策略加到Spring容器即可；
 *
 * @author mozping
 * @version 1.0
 * @date 2018/7/5 9:08
 * @see FeignHystrixConcurrencyStrategyIntellif
 * @since JDK1.8
 */
@Component
public class FeignHystrixConcurrencyStrategyIntellif extends HystrixConcurrencyStrategy {

    private static final Logger log = LoggerFactory.getLogger(FeignHystrixConcurrencyStrategyIntellif.class);
    private HystrixConcurrencyStrategy delegate;

    public FeignHystrixConcurrencyStrategyIntellif() {
        try {
            this.delegate = HystrixPlugins.getInstance().getConcurrencyStrategy();
            if (this.delegate instanceof FeignHystrixConcurrencyStrategyIntellif) {
                // 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();
            }
        }
    }
}

然后使用默认的熔断器隔离策略，也可以在拦截器内获取到上游服务的请求头信息了；
这里参考的博客，感谢这位大牛：https://blog.csdn.net/Crystalqy/article/details/79083857