最近在做项目的时候发现，微服务使用feign相互之间调用时，存在session丢失的问题。例如，使用feign调用某个远程api，这个远程api需要传递一个鉴权信息，我们可以把cookie里面的session信息放到header里面，这个header是动态的，跟你的httprequest相关，我们选择编写一个拦截器来实现header的传递，也就是需要实现requestinterceptor接口，具体代码如下：
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@configuration@enablefeignclients(basepackages = "com.xxx.xxx.client") public class feignclientsconfigurationcustom implements requestinterceptor { @override public void apply(requesttemplate template) { requestattributes requestattributes = requestcontextholder.getrequestattributes(); if (requestattributes == null) { return; } httpservletrequest request = ((servletrequestattributes) requestattributes).getrequest(); enumeration<string> headernames = request.getheadernames(); if (headernames != null) { while (headernames.hasmoreelements()) { string name = headernames.nextelement(); enumeration<string> values = request.getheaders(name); while (values.hasmoreelements()) { string value = values.nextelement(); template.header(name, value); } } } } } |
经过测试，上面的解决方案可以正常的使用；
但是，当引入hystrix熔断策略时，出现了一个新的问题：
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requestattributes requestattributes = requestcontextholder.getrequestattributes(); |
此时requestattributes会返回null，从而无法传递session信息，最终发现requestcontextholder.getrequestattributes()，该方法是从threadlocal变量里面取得对应信息的，这就找到问题原因了，是由于hystrix熔断机制导致的。
hystrix有2个隔离策略：thread以及semaphore，当隔离策略为 thread 时，是没办法拿到 threadlocal 中的值的。
因此有两种解决方案：
方案一：调整格隔离策略:
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hystrix.command.default.execution.isolation.strategy: semaphore |
这样配置后，feign可以正常工作。
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！ 可以参考官方文档说明。
方案二：自定义策略
记得之前在研究zipkin日志追踪的时候，看到过sleuth有自己的熔断机制，用来在thread之间传递trace信息，sleuth是可以拿到自己上下文信息的，查看源码找到了
org.springframework.cloud.sleuth.instrument.hystrix.sleuthhystrixconcurrencystrategy
这个类，查看sleuthhystrixconcurrencystrategy的源码，继承了hystrixconcurrencystrategy，用来实现了自己的并发策略。
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/** * abstract class for defining different behavior or implementations for concurrency related aspects of the system with default implementations. * <p> * for example, every {@link callable} executed by {@link hystrixcommand} will call {@link #wrapcallable(callable)} to give a chance for custom implementations to decorate the {@link callable} with * additional behavior. * <p> * when you implement a concrete {@link hystrixconcurrencystrategy}, you should make the strategy idempotent w.r.t threadlocals. * since the usage of threads by hystrix is internal, hystrix does not attempt to apply the strategy in an idempotent way. * instead, you should write your strategy to work idempotently. see https://github.com/netflix/hystrix/issues/351 for a more detailed discussion. * <p> * see {@link hystrixplugins} or the hystrix github wiki for information on configuring plugins: <a * href="https://github.com/netflix/hystrix/wiki/plugins" rel="external nofollow" >https://github.com/netflix/hystrix/wiki/plugins</a>. */public abstract class hystrixconcurrencystrategy |
搜索发现有好几个地方继承了hystrixconcurrencystrategy类
其中就有我们熟悉的spring security和刚才提到的sleuth都是使用了自定义的策略，同时由于hystrix只允许有一个并发策略，因此为了不影响spring security和sleuth，我们可以参考他们的策略实现自己的策略，大致思路：
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；
代码如下：
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public 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) { // 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(); } } } } |
最后，将这个策略类作为bean配置到feign的配置类feignclientsconfigurationcustom中
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@beanpublic feignhystrixconcurrencystrategy feignhystrixconcurrencystrategy() { return new feignhystrixconcurrencystrategy();} |
至此，结合feignclientsconfigurationcustom配置feign调用session丢失的问题完美解决。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/zl1zl2zl3/article/details/79084368
