Java tutorial
/* * Copyright 2014 Click Travel Ltd * * 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.clicktravel.cheddar.server.application.lifecycle; import static com.clicktravel.cheddar.server.application.lifecycle.LifecycleStatus.*; import java.util.Arrays; import java.util.Collection; import java.util.HashSet; import java.util.Set; import java.util.concurrent.CountDownLatch; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.context.ApplicationListener; import org.springframework.context.event.ContextRefreshedEvent; import org.springframework.stereotype.Component; import com.clicktravel.cheddar.infrastructure.messaging.MessageListener; /** * Controls the start and shutdown of all {@link MessageListeners}. This class progresses the lifecycle status of this * application instance when various enterXXXstate() methods are called. These methods are called by an external trigger * (system event handlers) under the control of a scripted blue-green deployment procedure. */ @Component public class LifecycleController implements ApplicationListener<ContextRefreshedEvent> { private final MessageListener eventMessageListener; private final MessageListener highPriorityEventMessageListener; private final MessageListener systemEventMessageListener; private final Collection<MessageListener> messageListeners; private final CountDownLatch restAdapterStartLatch; private final LifecycleStatusHolder lifecycleStatusHolder; private final TerminationThread terminationThread; private final Logger logger = LoggerFactory.getLogger(getClass()); @Autowired public LifecycleController(final MessageListener eventMessageListener, final MessageListener highPriorityEventMessageListener, final MessageListener systemEventMessageListener, final Collection<MessageListener> messageListeners, final CountDownLatch restAdapterStartLatch, final LifecycleStatusHolder lifecycleStatusHolder) { this.eventMessageListener = eventMessageListener; this.highPriorityEventMessageListener = highPriorityEventMessageListener; this.systemEventMessageListener = systemEventMessageListener; this.messageListeners = messageListeners; this.restAdapterStartLatch = restAdapterStartLatch; this.lifecycleStatusHolder = lifecycleStatusHolder; terminationThread = new TerminationThread(); } @Override public void onApplicationEvent(final ContextRefreshedEvent event) { final LifecycleStatus currentLifecycleStatus = lifecycleStatusHolder.getLifecycleStatus(); logger.debug("Initial lifecycle status: " + currentLifecycleStatus); systemEventMessageListener.start(); if (currentLifecycleStatus.equals(RUNNING)) { logger.debug("Application instances in this environment do not use blue-green deployment"); processRunningState(); } else { logger.debug("Application instances in this environment typically use blue-green deployment"); } } public void enterPausedState() { checkAndSetLifecycleStatus(INACTIVE, PAUSED); logger.debug( "Application instance now accepts REST requests, instance responds with positive health check. However, do not process REST requests."); } public void enterRunningState() { checkAndSetLifecycleStatus(PAUSED, RUNNING); processRunningState(); } public void enterRunningStateWithoutBlueGreenDeployment() { checkAndSetLifecycleStatus(INACTIVE, RUNNING); logger.debug("Skipping blue-green deployment procedure, proceeding directly to RUNNING state"); processRunningState(); } private void processRunningState() { startAll(messageListenersExcept(systemEventMessageListener)); logger.debug( "Application instance now running normally; REST application service requests are accepted and processed"); restAdapterStartLatch.countDown(); // start REST request processing } public void enterHaltingLowPriorityEventsState() { checkAndSetLifecycleStatus(RUNNING, HALTING_LOW_PRIORITY_EVENTS); logger.debug("Application instance closing down, using blue-green deployment procedure."); prepareAllMessageListenersForShutdown(); logger.debug("Halting low-priority domain event handling and general application work queue handling."); shutdownAll(messageListenersExcept(eventMessageListener, highPriorityEventMessageListener, systemEventMessageListener)); } public void enterDrainingRequestsState() { checkAndSetLifecycleStatus(HALTING_LOW_PRIORITY_EVENTS, DRAINING_REQUESTS); logger.debug( "Application instance now responds with negative health check, diverting REST requests away; Start to drain requests in progress."); } public void enterHaltingHighPriorityEventsState() { checkAndSetLifecycleStatus(DRAINING_REQUESTS, HALTING_HIGH_PRIORITY_EVENTS); terminationThread.start(); } private class TerminationThread extends Thread { @Override public void run() { processHaltingHighPriorityEventsState(); processTerminatingState(); processTerminatedState(); logger.info("Application instance terminated"); } } private void processHaltingHighPriorityEventsState() { logger.debug("Halting high-priority domain event processing"); shutdownAll(eventMessageListener, highPriorityEventMessageListener); eventMessageListener.awaitTermination(); highPriorityEventMessageListener.awaitTermination(); } private void processTerminatingState() { setLifecycleStatus(TERMINATING); logger.debug("Halting system queue processing"); systemEventMessageListener.shutdown(); systemEventMessageListener.awaitTermination(); } private void processTerminatedState() { setLifecycleStatus(TERMINATED); } private void checkAndSetLifecycleStatus(final LifecycleStatus expectedCurrentStatus, final LifecycleStatus newStatus) { final LifecycleStatus currentStatus = lifecycleStatusHolder.getLifecycleStatus(); if (currentStatus.equals(expectedCurrentStatus)) { setLifecycleStatus(newStatus); } else { logger.warn("Failed attempt to change lifecycle status from:[" + currentStatus + "] to:[" + newStatus + "]"); throw new IllegalStateException("Cannot change status from " + currentStatus + " to " + newStatus); } } private void setLifecycleStatus(final LifecycleStatus lifecycleStatus) { logger.debug("Changing lifecycle states; from:[" + lifecycleStatusHolder.getLifecycleStatus() + "] to:[" + lifecycleStatus + "]"); lifecycleStatusHolder.setLifecycleStatus(lifecycleStatus); } private void startAll(final Collection<MessageListener> messageListenersToStart) { for (final MessageListener messageListener : messageListenersToStart) { messageListener.start(); } } private void shutdownAll(final Collection<MessageListener> messageListenersToShutdown) { for (final MessageListener messageListener : messageListenersToShutdown) { messageListener.shutdown(); } } private void shutdownAll(final MessageListener... messageListenersToShutdown) { shutdownAll(Arrays.asList(messageListenersToShutdown)); } private void prepareAllMessageListenersForShutdown() { for (final MessageListener messageListener : messageListeners) { messageListener.prepareForShutdown(); } } private Set<MessageListener> messageListenersExcept(final MessageListener... exceptions) { final Set<MessageListener> result = new HashSet<>(messageListeners); result.removeAll(Arrays.asList(exceptions)); return result; } }