netflix-hystrix-简例

 

/**
 * CommandWithFallbackViaNetwork.run模拟远程调用失败，FallbackViaNetwork模拟需要通过网络从Redis获取老数据
 */
public class CommandWithFallbackViaNetwork extends HystrixCommand<String> {
    private final int id;

    protected CommandWithFallbackViaNetwork(int id) {
        //不设置ThreadPoolKey时，ThreadPoolKey默认为groupKey，不同的threadPoolKey代表不同的线程池。
        //A group name for a HystrixCommand. This is used for grouping together commands such as for reporting, alerting, dashboards or team/library ownership.
        super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("RemoteServiceX"))
                //A key to represent a HystrixCommand for monitoring, circuit-breakers, metrics publishing, caching and other such uses.
                .andCommandKey(HystrixCommandKey.Factory.asKey("GetValueCommand"))
                .andCommandPropertiesDefaults(HystrixCommandProperties.Setter()
                        .withExecutionIsolationStrategy(HystrixCommandProperties.ExecutionIsolationStrategy.THREAD)));
        this.id = id;
    }

    @Override
    protected String run() {
        //        remoteServiceXClient.getValue(id);
        //模拟远程调用失败
        throw new RuntimeException("force failure for example");
    }

    @Override
    protected String getFallback() {
        return new FallbackViaNetwork(id).execute();
    }

    private static class FallbackViaNetwork extends HystrixCommand<String> {
        private final int id;
        private static Map<Integer, String> memCacheClient = new ConcurrentHashMap<>();//充当Redis缓存，需要访问网络

        public FallbackViaNetwork(int id) {
            //groupKey与CommandWithFallbackViaNetwork一致，
            super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("RemoteServiceX"))
                    .andCommandKey(HystrixCommandKey.Factory.asKey("GetValueFallbackCommand"))
                    // use a different threadpool for the fallback command
                    // so saturating the RemoteServiceX pool won't prevent
                    // fallbacks from executing
                    .andThreadPoolKey(HystrixThreadPoolKey.Factory.asKey("RemoteServiceXFallback")));
            this.id = id;
        }

        @Override
        protected String run() {
            return memCacheClient.get(id);
        }

        @Override
        protected String getFallback() {
            // the fallback also failed
            // so this fallback-of-a-fallback will
            // fail silently and return null
            return null;
        }
    }
}