LoadBalancerFeignClient 中的 NullPointerException (spring-cloud-netflix) [英] NullPointerException in LoadBalancerFeignClient (spring-cloud-netflix)

问题描述

我们在我们的服务中为客户使用 Feign.最近其中一项服务开始随机抛出一些异常，原因如下:

We are using Feign for our clients in our services. Recently one of the services started to randomly throw some exceptions which is caused by:

Caused by: java.lang.NullPointerException: null
    at org.springframework.cloud.netflix.feign.ribbon.LoadBalancerFeignClient.execute(LoadBalancerFeignClient.java:63)
    at org.springframework.cloud.sleuth.instrument.web.client.feign.TraceLoadBalancerFeignClient.execute(TraceLoadBalancerFeignClient.java:41)
    at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:97)
    at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:76)
    at feign.hystrix.HystrixInvocationHandler$1.run(HystrixInvocationHandler.java:108)
    at com.netflix.hystrix.HystrixCommand$2.call(HystrixCommand.java:301)
    at com.netflix.hystrix.HystrixCommand$2.call(HystrixCommand.java:297)
    at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:46)
    at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:35)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
    at rx.Observable.unsafeSubscribe(Observable.java:10211)
    at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:51)
    at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:35)
    at rx.Observable.unsafeSubscribe(Observable.java:10211)
    at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:41)
    at rx.internal.operators.OnSubscribeDoOnEach.call(OnSubscribeDoOnEach.java:30)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
    at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
    at rx.Observable.unsafeSubscribe(Observable.java:10211)
    at rx.internal.operators.OperatorSubscribeOn$1.call(OperatorSubscribeOn.java:94)
    at com.netflix.hystrix.strategy.concurrency.HystrixContexSchedulerAction$1.call(HystrixContexSchedulerAction.java:56)
    at com.netflix.hystrix.strategy.concurrency.HystrixContexSchedulerAction$1.call(HystrixContexSchedulerAction.java:47)
    at our.code.hystrix.AuthContextAwareHystrixConcurrencyStrategy$AuthorizationContextAwareCallable.call(AuthContextAwareHystrixConcurrencyStrategy.java:57)
    at org.springframework.cloud.sleuth.instrument.hystrix.SleuthHystrixConcurrencyStrategy$HystrixTraceCallable.call(SleuthHystrixConcurrencyStrategy.java:154)
    at com.netflix.hystrix.strategy.concurrency.HystrixContexSchedulerAction.call(HystrixContexSchedulerAction.java:69)
    at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)

我查看了 spring-cloud-netflix-core (v1.2.2.RELEASE) 代码及其依赖项，但无法弄清楚 NPE 发生的原因.在堆栈跟踪中，它指向 LoadBalancerFeignClient 中的第 63 行，即:

I took a look a spring-cloud-netflix-core (v1.2.2.RELEASE) code and its dependencies, but cannot figure out why the NPE is happening. In the stack trace it's pointing to Line 63 in LoadBalancerFeignClient which is:

private CachingSpringLoadBalancerFactory lbClientFactory;

@Override
public Response execute(Request request, Request.Options options) throws IOException {
  try {
    URI asUri = URI.create(request.url());
    String clientName = asUri.getHost();
    URI uriWithoutHost = cleanUrl(request.url(), clientName);
    FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
        this.delegate, request, uriWithoutHost);

    IClientConfig requestConfig = getClientConfig(options, clientName);
    return lbClient(clientName).executeWithLoadBalancer(ribbonRequest, // Line 63
        requestConfig).toResponse();
  }
  catch (ClientException e) {
    IOException io = findIOException(e);
    if (io != null) {
      throw io;
    }
    throw new RuntimeException(e);
  }
}

private FeignLoadBalancer lbClient(String clientName) {
  return this.lbClientFactory.create(clientName);
}

这意味着只有 lbClient(clientName) 是一个可能返回 null 的地方.查看 CachingSpringLoadBalancerFactory 类及其实现，我在 ConcurrentReferenceHashMap 的文档中发现了这一点:

which means only lbClient(clientName) is the one possible place returning null. Looking at CachingSpringLoadBalancerFactory class and its implementation, I found this in the documentation of ConcurrentReferenceHashMap:

注意:引用的使用意味着不能保证放置到地图中的项目随后将可用.垃圾收集器可能会随时丢弃引用，因此可能会出现未知线程正在悄悄删除条目.

NOTE: The use of references means that there is no guarantee that items placed into the map will be subsequently available. The garbage collector may discard references at any time, so it may appear that an unknown thread is silently removing entries.

现在我的问题是它为什么会发生以及如何解决它.谢谢.

Now my question is why it's happening and how to solve it. Thanks.

推荐答案

为了记录，这是 GitHub 上的问题:https://github.com/spring-cloud/spring-cloud-Netflix/问题/2443虽然在新版本中修复了.

For the record, this the issue on GitHub: https://github.com/spring-cloud/spring-cloud-netflix/issues/2443 Though it is fixed in the new version.

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