<dependency>
    <groupId>com.netflix.hystrix</groupId>
    <artifactId>hystrix-core</artifactId>
    <version>1.5.12</version>
</dependency>

package com.roncoo.eshop.cache.ha.hystrix.command;

import org.springframework.boot.context.embedded.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;
import com.netflix.hystrix.HystrixCommandKey;
import com.netflix.hystrix.HystrixCommandProperties;
import com.netflix.hystrix.HystrixRequestCache;
import com.netflix.hystrix.HystrixThreadPoolKey;
import com.netflix.hystrix.HystrixThreadPoolProperties;
import com.netflix.hystrix.HystrixCommandProperties.ExecutionIsolationStrategy;
import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategyDefault;
import com.roncoo.eshop.cache.ha.filter.HystrixRequestContextFilter;

/** 
 * @ClassName: HystrixCommandDemo 
 * @date 2018年12月15日 下午2:17:51 
 */
public class HystrixCommandDemo extends HystrixCommand<String> {

	private String key;
	private static final HystrixCommandKey COMMAND_KEY = HystrixCommandKey.Factory.asKey("key");

	public HystrixCommandDemo(String key) {
		super(Setter
				.withGroupKey(HystrixCommandGroupKey.Factory.asKey("groupKeyName"))
				.andCommandKey(COMMAND_KEY)
				.andThreadPoolKey(HystrixThreadPoolKey.Factory.asKey("threadPoolKey"))
				.andThreadPoolPropertiesDefaults(HystrixThreadPoolProperties.Setter().withCoreSize(10).withQueueSizeRejectionThreshold(10))
				.andCommandPropertiesDefaults(
						HystrixCommandProperties.Setter().withFallbackIsolationSemaphoreMaxConcurrentRequests(20).withExecutionTimeoutEnabled(true)
								.withExecutionTimeoutInMilliseconds(1000).withExecutionIsolationStrategy(ExecutionIsolationStrategy.SEMAPHORE)
								.withExecutionIsolationSemaphoreMaxConcurrentRequests(15).withCircuitBreakerEnabled(true)
								.withCircuitBreakerRequestVolumeThreshold(20).withCircuitBreakerRequestVolumeThreshold(50)
								.withCircuitBreakerSleepWindowInMilliseconds(5000).withCircuitBreakerErrorThresholdPercentage(50)
								.withCircuitBreakerForceOpen(false).withCircuitBreakerForceClosed(false)));
		// 组名，统一管理命令，比如报告、警报、仪表盘和。默认情况下，HystrixCommandGroupKey的名字即为线程池的名字，除非自定义线程池
		Setter setter = Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("groupKeyName"));
		// 命令的名称
		setter.andCommandKey(COMMAND_KEY);
		// 不指定线程池时，hystrix会默认以HystrixCommandGroupKey创建一个，一个HystrixCommand与一个HystrixThreadPoolKey相关联
		setter.andThreadPoolKey(HystrixThreadPoolKey.Factory.asKey("threadPoolKey"));
		// 线程池核心线程数及队列容量
		setter.andThreadPoolPropertiesDefaults(HystrixThreadPoolProperties.Setter().withCoreSize(10).withQueueSizeRejectionThreshold(10));
		// fallback降级信号量数
		setter.andCommandPropertiesDefaults(HystrixCommandProperties.Setter().withFallbackIsolationSemaphoreMaxConcurrentRequests(20));
		// 是否开启command超时，默认为true
		// 设置command执行超时时间，如果超时，将调用fallback降级
		setter.andCommandPropertiesDefaults(HystrixCommandProperties.Setter().withExecutionTimeoutEnabled(true).withExecutionTimeoutInMilliseconds(1000));
		// 信号量资源隔离与限流
		setter.andCommandPropertiesDefaults(HystrixCommandProperties.Setter().withExecutionIsolationStrategy(ExecutionIsolationStrategy.SEMAPHORE)
				.withExecutionIsolationSemaphoreMaxConcurrentRequests(15));
		// 是否允许断路器工作，包括跟踪服务调用的健康状况、异常请求过多是否允许开启断路器，默认为true
		// 最少要有多少个请求才触发断路器，默认值为20；
		// 短路之后，在多少毫秒之内对请求直接reject，然后在这段时间之后，引导断路器half-open，尝试自动恢复，默认值5000毫秒；
		// 设置异常请求量百分比，当异常请求达到这个百分比，开启断路器，默认50%；
		// 是否手动打开断路器，默认false；
		// 是否手动关闭断路器，默认false；
		setter.andCommandPropertiesDefaults(HystrixCommandProperties.Setter().withCircuitBreakerEnabled(true).withCircuitBreakerRequestVolumeThreshold(20)
				.withCircuitBreakerSleepWindowInMilliseconds(5000).withCircuitBreakerErrorThresholdPercentage(50).withCircuitBreakerForceOpen(false)
				.withCircuitBreakerForceClosed(false));
		this.key = key;

	}

	@Override
	protected String run() throws Exception {
		return null;
	}

	/**
	 * request cache，对每一次请求，都初始化一个hystrix的请求上下文，java web通常用filter来实现
	 * public class HystrixRequestContextFilter implements Filter {
			public void init(FilterConfig config) throws ServletException {
			}
			public void doFilter(ServletRequest request, ServletResponse response,
					FilterChain chain) throws IOException, ServletException {
				HystrixRequestContext context = HystrixRequestContext.initializeContext();
				try {
					chain.doFilter(request, response); 
				} catch (Exception e) {
					e.printStackTrace();
				} finally {
					context.shutdown();
				}
			}
			public void destroy() {
			}
		}
		@Bean
	    public FilterRegistrationBean filterRegistrationBean() {
	    	FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(
	    			new HystrixRequestContextFilter());
	    	filterRegistrationBean.addUrlPatterns("/*");
	    	return filterRegistrationBean;
	    }
	 * @Title: getCacheKey 
	 * @see com.netflix.hystrix.AbstractCommand#getCacheKey() 
	 * @return  
	 */
	@Override
	protected String getCacheKey() {
		return "key:" + key;
	}

	/**
	 * 手动删除hystrix的request cache
	 * @Title: flushCacheKey 
	 * @param key  
	 */
	public static void flushCacheKey(String key) {
		HystrixRequestCache.getInstance(COMMAND_KEY, HystrixConcurrencyStrategyDefault.getInstance()).clear(key);
	}

	/**
	 * 通过信号量控制并发请求的降级，默认是10，如果超过了10，则会reject
	 * 可以通过.andCommandPropertiesDefaults(HystrixCommandProperties.Setter().withFallbackIsolationSemaphoreMaxConcurrentRequests(20))配置
	 * @Title: getFallback 
	 * @see com.netflix.hystrix.HystrixCommand#getFallback() 
	 * @return  
	 */
	@Override
	protected String getFallback() {
		return null;
	}
}