hystrix(4) properties配置
这一节我们来讲hystrix的properties配置体系，properties配置也是各个功能模块的基础功能。hystrix将配置分成三个部分：
1.HystrixCommandProperties用于HystrixCommand配置，一个HystrixCommandKey对应一个HystrixCommandProperties实例。
2.HystrixThreadPoolProperties用于HystrixThreadPool配置，一个HystrixThreadPoolKey对应一个HystrixThreadPoolProperties实例。
3.HystrixCollapserProperties用于HystrixCollapserCommand配置，一个HystrixCollapserKey对应一个HystrixCollapserProperties实例。
| 类别 | 配置项 | 默认值 | 说明 |
| HystrixCommandProperties |
hystrix.threadpool.[commandkey].circuitBreaker.enabled |
true | |
| hystrix.threadpool.[commandkey].circuitBreaker.requestVolumeThreshold | 20 | ||
| hystrix.threadpool.[commandkey].circuitBreaker.sleepWindowInMilliseconds | 5000 | ||
| hystrix.threadpool.[commandkey].circuitBreaker.errorThresholdPercentage | 50 | ||
| hystrix.threadpool.[commandkey].circuitBreaker.forceOpen | false | ||
| hystrix.threadpool.[commandkey].circuitBreaker.forceClosed | false | ||
| hystrix.threadpool.[commandkey].execution.isolation.strategy | Thread | ||
| hystrix.threadpool.[commandkey].execution.isolation.thread.timeoutInMilliseconds | 1000 | ||
| hystrix.threadpool.[commandkey].execution.timeout.enabled | true | ||
| hystrix.threadpool.[commandkey].execution.isolation.thread.interruptOnTimeout | true | ||
| hystrix.threadpool.[commandkey].execution.isolation.thread.interruptOnFutureCancel | false | ||
| hystrix.threadpool.[commandkey].execution.isolation.semaphore.maxConcurrentRequests | 10 | ||
| hystrix.threadpool.[commandkey].fallback.isolation.semaphore.maxConcurrentRequests | 10 | ||
| hystrix.threadpool.[commandkey].fallback.enabled | true | ||
| hystrix.threadpool.[commandkey].metrics.rollingStats.timeInMilliseconds | 10000 | ||
| hystrix.threadpool.[commandkey].metrics.rollingStats.numBuckets | 10 | ||
| hystrix.threadpool.[commandkey].metrics.rollingPercentile.enabled | true | ||
| hystrix.threadpool.[commandkey].metrics.rollingPercentile.timeInMilliseconds | 60000 | ||
| hystrix.threadpool.[commandkey].metrics.rollingPercentile.numBuckets | 6 | ||
| hystrix.threadpool.[commandkey].metrics.rollingPercentile.bucketSize | 100 | ||
| hystrix.threadpool.[commandkey].metrics.healthSnapshot.intervalInMilliseconds | 500 | ||
| hystrix.threadpool.[commandkey].requestCache.enabled | true | ||
| hystrix.threadpool.[commandkey].requestLog.enabled | true | ||
| hystrix.threadpool.[commandkey].threadPoolKeyOverride | |||
| HystrixThreadPoolProperties | hystrix.threadpool.[threadPoolkey].coreSize | 10 | |
| hystrix.threadpool.[threadPoolkey].allowMaximumSizeToDivergeFromCoreSize | false | ||
| hystrix.threadpool.[threadPoolkey].maximumSize | 10 | ||
| hystrix.threadpool.[threadPoolkey].keepAliveTimeMinutes | 1 | ||
| hystrix.threadpool.[threadPoolkey].maxQueueSize | -1 | ||
| hystrix.threadpool.[threadPoolkey].queueSizeRejectionThreshold | 5 | ||
| hystrix.threadpool.[threadPoolkey].metrics.rollingStats.timeInMilliseconds | 10000 | ||
| hystrix.threadpool.[threadPoolkey].metrics.rollingStats.numBuckets | 10 | ||
| HystrixCollapserProperties | hystrix.collapser.[collapserCommandkey].maxRequestsInBatch | Integer.MAX_VALUE | |
| hystrix.collapser.[collapserCommandkey].timerDelayInMilliseconds | 10 | ||
| hystrix.collapser.[collapserCommandkey].requestCache.enabled | true | ||
| hystrix.collapser.[collapserCommandkey].metrics.rollingStats.timeInMilliseconds | 10000 | ||
| hystrix.collapser.[collapserCommandkey].metrics.rollingStats.numBuckets | 10 | ||
| hystrix.collapser.[collapserCommandkey].metrics.rollingPercentile.enabled | true | ||
| hystrix.collapser.[collapserCommandkey].metrics.rollingPercentile.timeInMilliseconds | 60000 | ||
| hystrix.collapser.[collapserCommandkey].metrics.rollingPercentile.numBuckets | 6 | ||
| hystrix.collapser.[collapserCommandkey].metrics.rollingPercentile.bucketSize | 100 |
内部每个属性由一个ChainHystrixProperty表示，ChainHystrixProperty是一个串联的HystrixDynamicProperty，持续获取串中的属性值，直到获得不为null值为止。ChainHystrixProperty串联的HystrixDynamicProperty默认通过插件获取的HystrixDynamicProperties获取（最后我们会讲到插件）。
HystrixDynamicProperty表示动态配置数据，如果配置源发送变化，通过该对象获取配置也会相应变化。hystrix中有种实现类：
1.通过archaius实现获取配置项，通过HystrixDynamicPropertiesArchaius创建该类HystrixDynamicProperty。
2.通过system实现获取配置项，通过HystrixDynamicPropertiesSystemProperties创建该类HystrixDynamicProperty。
