CommandCollapserGetValueForKey.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 java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.Future;

import org.junit.Test;

import com.netflix.hystrix.HystrixCollapser;
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.strategy.concurrency.HystrixRequestContext;

/**
 * Sample {@link HystrixCollapser} that automatically batches multiple requests to execute()/queue()
 * into a single {@link HystrixCommand} execution for all requests within the defined batch (time or size).
 */
public class CommandCollapserGetValueForKey extends HystrixCollapser<List<String>, String, Integer> {

    private final Integer key;

    public CommandCollapserGetValueForKey(Integer key) {
        this.key = key;
    }

    @Override
    public Integer getRequestArgument() {
        return key;
    }

    @Override
    protected HystrixCommand<List<String>> createCommand(final Collection<CollapsedRequest<String, Integer>> requests) {
        return new BatchCommand(requests);
    }

    @Override
    protected void mapResponseToRequests(List<String> batchResponse, Collection<CollapsedRequest<String, Integer>> requests) {
        int count = 0;
        for (CollapsedRequest<String, Integer> request : requests) {
            request.setResponse(batchResponse.get(count++));
        }
    }

    private static final class BatchCommand extends HystrixCommand<List<String>> {
        private final Collection<CollapsedRequest<String, Integer>> requests;

        private BatchCommand(Collection<CollapsedRequest<String, Integer>> requests) {
            super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"))
                    .andCommandKey(HystrixCommandKey.Factory.asKey("GetValueForKey")));
            this.requests = requests;
        }

        @Override
        protected List<String> run() {
            ArrayList<String> response = new ArrayList<String>();
            for (CollapsedRequest<String, Integer> request : requests) {
                // artificial response for each argument received in the batch
                response.add("ValueForKey: " + request.getArgument());
            }
            return response;
        }
    }

    public static class UnitTest {

        @Test
        public void testCollapser() throws Exception {
            HystrixRequestContext context = HystrixRequestContext.initializeContext();
            try {
                Future<String> f1 = new CommandCollapserGetValueForKey(1).queue();
                Future<String> f2 = new CommandCollapserGetValueForKey(2).queue();
                Future<String> f3 = new CommandCollapserGetValueForKey(3).queue();
                Future<String> f4 = new CommandCollapserGetValueForKey(4).queue();

                assertEquals("ValueForKey: 1", f1.get());
                assertEquals("ValueForKey: 2", f2.get());
                assertEquals("ValueForKey: 3", f3.get());
                assertEquals("ValueForKey: 4", f4.get());

                int numExecuted = HystrixRequestLog.getCurrentRequest().getAllExecutedCommands().size();

                System.err.println("num executed: " + numExecuted);

                // assert that the batch command 'GetValueForKey' was in fact executed and that it executed only 
                // once or twice (due to non-determinism of scheduler since this example uses the real timer)
                if (numExecuted > 2) {
                    fail("some of the commands should have been collapsed");
                }

                System.err.println("HystrixRequestLog.getCurrentRequest().getAllExecutedCommands(): " + HystrixRequestLog.getCurrentRequest().getAllExecutedCommands());

                int numLogs = 0;
                for (HystrixInvokableInfo<?> command : HystrixRequestLog.getCurrentRequest().getAllExecutedCommands()) {
                    numLogs++;
                    
                    // assert the command is the one we're expecting
                    assertEquals("GetValueForKey", command.getCommandKey().name());

                    System.err.println(command.getCommandKey().name() + " => command.getExecutionEvents(): " + command.getExecutionEvents());

                    // confirm that it was a COLLAPSED command execution
                    assertTrue(command.getExecutionEvents().contains(HystrixEventType.COLLAPSED));
                    assertTrue(command.getExecutionEvents().contains(HystrixEventType.SUCCESS));
                }

                assertEquals(numExecuted, numLogs);
            } finally {
                context.shutdown();
            }
        }
    }
}