最近在做項目的時候發現，微服務使用feign相互之間調用時，存在session丟失的問題。例如，使用feign調用某個遠程api，這個遠程api需要傳遞一個鑒權信息，我們可以把cookie里面的session信息放到header里面，這個header是動態的，跟你的httprequest相關，我們選擇編寫一個攔截器來實現header的傳遞，也就是需要實現requestinterceptor接口，具體代碼如下：
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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); } } } } } |
經過測試，上面的解決方案可以正常的使用；
但是，當引入hystrix熔斷策略時，出現了一個新的問題：
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requestattributes requestattributes = requestcontextholder.getrequestattributes(); |
此時requestattributes會返回null，從而無法傳遞session信息，最終發現requestcontextholder.getrequestattributes()，該方法是從threadlocal變量里面取得對應信息的，這就找到問題原因了，是由于hystrix熔斷機制導致的。
hystrix有2個隔離策略：thread以及semaphore，當隔離策略為 thread 時，是沒辦法拿到 threadlocal 中的值的。
因此有兩種解決方案：
方案一：調整格隔離策略:
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hystrix.command.default.execution.isolation.strategy: semaphore |
這樣配置后，feign可以正常工作。
但該方案不是特別好。原因是hystrix官方強烈建議使用thread作為隔離策略！ 可以參考官方文檔說明。
方案二：自定義策略
記得之前在研究zipkin日志追蹤的時候，看到過sleuth有自己的熔斷機制，用來在thread之間傳遞trace信息，sleuth是可以拿到自己上下文信息的，查看源碼找到了
org.springframework.cloud.sleuth.instrument.hystrix.sleuthhystrixconcurrencystrategy
這個類，查看sleuthhystrixconcurrencystrategy的源碼，繼承了hystrixconcurrencystrategy，用來實現了自己的并發策略。
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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 |
搜索發現有好幾個地方繼承了hystrixconcurrencystrategy類
其中就有我們熟悉的spring security和剛才提到的sleuth都是使用了自定義的策略，同時由于hystrix只允許有一個并發策略，因此為了不影響spring security和sleuth，我們可以參考他們的策略實現自己的策略，大致思路：
將現有的并發策略作為新并發策略的成員變量；
在新并發策略中，返回現有并發策略的線程池、queue；
代碼如下：
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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，將這個策略類作為bean配置到feign的配置類feignclientsconfigurationcustom中
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@beanpublic feignhystrixconcurrencystrategy feignhystrixconcurrencystrategy() { return new feignhystrixconcurrencystrategy();} |
至此，結合feignclientsconfigurationcustom配置feign調用session丟失的問題完美解決。
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
原文鏈接：https://blog.csdn.net/zl1zl2zl3/article/details/79084368
