Hystrix提供了熔断、隔离、Fallback、cache、监控等功能，能够在一个、或多个依赖同时出现问题时保证系统依然可用。
将服务的接口使用hystrix线程池做隔离，可以实现限流和熔断的效果。配合天舟平台提供的SpringCloudConfig配置中心，可以在不重启服务的情况下，动态调整hystrix限流的参数。
springboot工程使用hystrix的配置步骤:
1.pom.xml:
<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-hystrix</artifactId> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-hystrix-dashboard</artifactId> </dependency> 2.开启hystrix及hystrixDashboard:
入口类加注解，@EnableHystrix,@EnableHystrixDashboard @SpringBootApplication @EnableHystrix @EnableHystrixDashboard public class ContestDemoApplication{ public static void main(String[] args) { SpringApplication.run(ContestDemoApplication.class, args); } } 3.@HystrixCommand注解:
@HystrixCommand 加到服务的接口方法上，可以对接口限流。 下面的代码，给服务的 /hello接口 加了hystrix线程隔离，并且限制并发为5。 当接口熔断或者降级时，会走降级方法，降级方法将异常信息返回，并且返回状态码 503 @RestController @RequestMapping(value = "/contest/demo") public class HelloController { //对controller层的接口做hystrix线程池隔离，可以起到限流的作用 @HystrixCommand( commandKey = "helloCommand",//缺省为方法名 threadPoolKey = "helloPool",//缺省为类名 fallbackMethod = "fallbackMethod",//指定降级方法，在熔断和异常时会走降级方法 commandProperties = { //超时时间 @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "1000") }, threadPoolProperties = { //并发，缺省为10 @HystrixProperty(name = "coreSize", value = "5") } ) @RequestMapping( value = "/hello", method = RequestMethod.GET ) public String sayHello(HttpServletResponse httpServletResponse){ return "Hello World!：00000"; } /** * 降级方法，状态码返回503 * 注意，降级方法的返回类型与形参要与原方法相同，可以多一个Throwable参数放到最后，用来获取异常信息 */ public String fallbackMethod(HttpServletResponse httpServletResponse,Throwable e){ httpServletResponse.setStatus(HttpStatus.SERVICE_UNAVAILABLE.value()); return e.getMessage(); } } hystrix的属性配置:
如果将@HystrixCommand注解加到方法上，不对属性（如CoreSize）做任何配置，那么相当于使用了如下缺省配置。 每个属性的意义可以参考 hystrix学习资料 @HystrixCommand( commandProperties = { //execution @HystrixProperty(name = "execution.isolation.strategy", value = "THREAD"), @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "1000"), @HystrixProperty(name = "execution.timeout.enabled", value = "true"), @HystrixProperty(name = "execution.isolation.thread.interruptOnTimeout", value = "true"), @HystrixProperty(name = "execution.isolation.thread.interruptOnCancel", value = "false"), @HystrixProperty(name = "execution.isolation.semaphore.maxConcurrentRequests", value = "10"), //fallback @HystrixProperty(name = "fallback.isolation.semaphore.maxConcurrentRequests", value = "10"), @HystrixProperty(name = "fallback.enabled", value = "true"), //circuit breaker @HystrixProperty(name = "circuitBreaker.enabled", value = "true"), @HystrixProperty(name = "circuitBreaker.forceClosed", value = "false"), @HystrixProperty(name = "circuitBreaker.forceOpen", value = "false"), @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold", value = "20"), @HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds", value = "5000"), @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage", value = "50"), //Metrics @HystrixProperty(name = "metrics.rollingStats.timeInMilliseconds", value = "10000"), @HystrixProperty(name = "metrics.rollingStats.numBuckets", value = "10"), @HystrixProperty(name = "metrics.rollingPercentile.enabled", value = "true"), @HystrixProperty(name = "metrics.rollingPercentile.timeInMilliseconds", value = "60000"), @HystrixProperty(name = "metrics.rollingPercentile.numBuckets", value = "6"), @HystrixProperty(name = "metrics.rollingPercentile.bucketSize", value = "100"), @HystrixProperty(name = "metrics.healthSnapshot.intervalInMilliseconds", value = "500"), //request context @HystrixProperty(name = "requestCache.enabled", value = "true"), @HystrixProperty(name = "requestLog.enabled", value = "true")}, threadPoolProperties = { @HystrixProperty(name = "coreSize", value = "10"), @HystrixProperty(name = "maximumSize", value = "10"), @HystrixProperty(name = "maxQueueSize", value = "-1"), @HystrixProperty(name = "queueSizeRejectionThreshold", value = "5"), @HystrixProperty(name = "keepAliveTimeMinutes", value = "1"), @HystrixProperty(name = "allowMaximumSizeToDivergeFromCoreSize", value = "false"), @HystrixProperty(name = "metrics.rollingStats.timeInMilliseconds", value = "10000"), @HystrixProperty(name = "metrics.rollingStats.numBuckets", value = "10") } ) 如果要自定义这些属性，那么需要先了解下hystrix属性配置的优先级。 4 个不同优先级别的配置（优先级由低到高）。
全局配置属性：通过在配置文件中定义全局属性值， 在应用启动时或可用Spring Cloud Config和服务本身的动态刷新接口实现的动态刷新配置功能下， 可以实现对“全局默认值”的覆盖以及在运行期对“全局默认值”的动态调整。
如下是 threadpool 和 command下的属性全局配置，注意具体的配置都在 default 下 #hystrix全局属性配置 hystrix: threadpool: default: #对应@HystrixCommand注解中threadPoolKey的属性值，默认为default coreSize: 50 #线程池的核心线程数及并发执行的最大线程数 command: default: #对应@HystrixCommand注解中commandKey的属性值，默认为default execution: isolation: thread: timeoutInMilliseconds: 1000 #执行超时时间 fallback: isolation: semaphore: maxConcurrentRequests: 1000 #任意时间点允许的降级方法并发数。当请求达到或超过该设置值其余请求不会调用fallback而是直接被拒绝 实例默认值：通过代码为实例定义的默认值。 通过代码的方式为实例设置属性值来覆盖默认的全局配置。
示例如下： @HystrixCommand( commandKey = "helloCommand",//缺省为方法名 threadPoolKey = "helloPool",//缺省为类名 fallbackMethod = "fallbackMethod",//指定降级方法，在熔断和异常时会走降级方法 commandProperties = { //超时时间 @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds", value = "1000") }, threadPoolProperties = { //并发，缺省为10 @HystrixProperty(name = "coreSize", value = "5") } ) @RequestMapping( value = "/hello", method = RequestMethod.GET ) public String sayHello(HttpServletResponse httpServletResponse){ return "Hello World!：00000"; } 实例配置属性：通过配置文件来为指定的实例进行属性配置， 以覆盖前面的三个默认值。 它也可用Spring Cloud Config和服务本身的动态刷新接口实现的动态刷新配置功能，实现对具体实例配置的动态调整。
以示例代码中的 /hello 接口为例， commandKey=helloCommand threadPoolKey=helloPool,那么对其的配置如下 #hystrix参数配置 hystrix: threadpool: helloPool: #注解中的threadPoolKey属性值, 如有特殊配置不想使用defualt默认配置可自行添加 coreSize: 20 command: helloCommand: #注解中的commandKey属性值,如有特殊配置不想使用默认配置可自行添加 execution: isolation: thread: timeoutInMilliseconds: 4000 #执行超时时间 文章来源: Hystrix实现限流和熔断