CommandWithFallbackViaNetwork.java

/**
 * Copyright 2012 Netflix, Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.netflix.hystrix.examples.basic;

import static org.junit.Assert.*;

import org.junit.Test;

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;
import com.netflix.hystrix.HystrixCommandKey;
import com.netflix.hystrix.HystrixEventType;
import com.netflix.hystrix.HystrixInvokableInfo;
import com.netflix.hystrix.HystrixRequestLog;
import com.netflix.hystrix.HystrixThreadPoolKey;
import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;

/**
 * Sample {@link HystrixCommand} that implements fallback logic that requires
 * network traffic and thus executes another {@link HystrixCommand} from the {@link #getFallback()} method.
 * <p>
 * Note also that the fallback command uses a separate thread-pool as well even though
 * it's in the same command group.
 * <p>
 * It needs to be on a separate thread-pool otherwise the first command could saturate it
 * and the fallback command never have a chance to execute.
 */
public class CommandWithFallbackViaNetwork extends HystrixCommand<String> {
    private final int id;

    protected CommandWithFallbackViaNetwork(int id) {
        super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("RemoteServiceX"))
                .andCommandKey(HystrixCommandKey.Factory.asKey("GetValueCommand")));
        this.id = id;
    }

    @Override
    protected String run() {
        //        RemoteServiceXClient.getValue(id);
        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;

        public FallbackViaNetwork(int id) {
            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() {
            //            MemCacheClient.getValue(id);
            throw new RuntimeException("the fallback also failed");
        }

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

    public static class UnitTest {

        @Test
        public void test() {
            HystrixRequestContext context = HystrixRequestContext.initializeContext();
            try {
                assertEquals(null, new CommandWithFallbackViaNetwork(1).execute());

                HystrixInvokableInfo<?> command1 = HystrixRequestLog.getCurrentRequest().getAllExecutedCommands().toArray(new HystrixInvokableInfo<?>[2])[0];
                assertEquals("GetValueCommand", command1.getCommandKey().name());
                assertTrue(command1.getExecutionEvents().contains(HystrixEventType.FAILURE));

                HystrixInvokableInfo<?> command2 = HystrixRequestLog.getCurrentRequest().getAllExecutedCommands().toArray(new HystrixInvokableInfo<?>[2])[1];
                assertEquals("GetValueFallbackCommand", command2.getCommandKey().name());
                assertTrue(command2.getExecutionEvents().contains(HystrixEventType.FAILURE));
            } finally {
                context.shutdown();
            }
        }
    }
}