最近做一个项目,用到springCloud,结果遇到session丢失的问题,从zuul->feign->shiro->boot都有问题,默认情况下,zuul和feign在转发时都会丢掉header,于是花时间研究下。
转:https://blog.csdn.net/Crystalqy/article/details/79083857
自定义RequestInterceptor
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:
@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:
RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
获取不到request信息,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,由于Hystrix熔断机制导致的。
Hystrix有隔离策略: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
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。
/**
* 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">https://github.com/Netflix/Hystrix/wiki/Plugins</a>.
*/
public abstract class HystrixConcurrencyStrategy
搜索发现有好几个地方继承HystrixConcurrencyStrategy类
image.png
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侧路,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:
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();
}
}
}
}
至此,结合FeignClientsConfigurationCustom配置feign调用session丢失的问题完美解决。
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