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);
}
}
}
}
}
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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();
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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
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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
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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();
}
}
}
}
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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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@bean
public feignhystrixconcurrencystrategy feignhystrixconcurrencystrategy() {
return new feignhystrixconcurrencystrategy();
}
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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