Get-Set-Get with Request Cache Invalidation

假如需要一个Get-Set-Get的场景。Get 接收需要足够的流量，要求对其缓存。但是有时候Set发生在其它的command里。在同一请求中缓存需要失效，这就需要通过调用 HystrixRequestCache.clear()实现。

以下是实现示例

public class CommandUsingRequestCacheInvalidation {

    /* represents a remote data store */
    private static volatile String prefixStoredOnRemoteDataStore = "ValueBeforeSet_";

    public static class GetterCommand extends HystrixCommand<String> {

        private static final HystrixCommandKey GETTER_KEY = HystrixCommandKey.Factory.asKey("GetterCommand");
        private final int id;

        public GetterCommand(int id) {
            super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("GetSetGet"))
                    .andCommandKey(GETTER_KEY));
            this.id = id;
        }

        @Override
        protected String run() {
            return prefixStoredOnRemoteDataStore + id;
        }

        @Override
        protected String getCacheKey() {
            return String.valueOf(id);
        }

        /**
         * Allow the cache to be flushed for this object.
         *
         * @param id
         *            argument that would normally be passed to the command
         */
        public static void flushCache(int id) {
            HystrixRequestCache.getInstance(GETTER_KEY,
                    HystrixConcurrencyStrategyDefault.getInstance()).clear(String.valueOf(id));
        }

    }

    public static class SetterCommand extends HystrixCommand<Void> {

        private final int id;
        private final String prefix;

        public SetterCommand(int id, String prefix) {
            super(HystrixCommandGroupKey.Factory.asKey("GetSetGet"));
            this.id = id;
            this.prefix = prefix;
        }

        @Override
        protected Void run() {
            // persist the value against the datastore
            prefixStoredOnRemoteDataStore = prefix;
            // flush the cache
            GetterCommand.flushCache(id);
            // no return value
            return null;
        }
    }
}

单元测试

 @Test
        public void getGetSetGet() {
            HystrixRequestContext context = HystrixRequestContext.initializeContext();
            try {
                assertEquals("ValueBeforeSet_1", new GetterCommand(1).execute());
                GetterCommand commandAgainstCache = new GetterCommand(1);
                assertEquals("ValueBeforeSet_1", commandAgainstCache.execute());
                // confirm it executed against cache the second time
                assertTrue(commandAgainstCache.isResponseFromCache());
                // set the new value
                new SetterCommand(1, "ValueAfterSet_").execute();
                // fetch it again
                GetterCommand commandAfterSet = new GetterCommand(1);
                // the getter should return with the new prefix, not the value from cache
                assertFalse(commandAfterSet.isResponseFromCache());
                assertEquals("ValueAfterSet_1", commandAfterSet.execute());
            } finally {
                context.shutdown();
            }
        }
    }