Java tutorial
/* * Copyright 2014-2017 the original author or authors. * * 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 org.springframework.integration.zookeeper.leader; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.imps.CuratorFrameworkState; import org.apache.curator.framework.recipes.leader.LeaderSelector; import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter; import org.springframework.context.SmartLifecycle; import org.springframework.integration.leader.Candidate; import org.springframework.integration.leader.Context; import org.springframework.integration.leader.event.LeaderEventPublisher; import org.springframework.util.StringUtils; /** * Bootstrap leadership {@link Candidate candidates} * with ZooKeeper/Curator. Upon construction, {@link #start} must be invoked to * register the candidate for leadership election. * * @author Patrick Peralta * @author Janne Valkealahti * @author Gary Russell * @author Artem Bilan * * @since 4.2 */ public class LeaderInitiator implements SmartLifecycle { private static final Log logger = LogFactory.getLog(LeaderInitiator.class); private static final String DEFAULT_NAMESPACE = "/spring-integration/leader/"; private static final Context NULL_CONTEXT = () -> false; private final CuratorContext context = new CuratorContext(); /** * Curator client. */ private final CuratorFramework client; /** * Candidate for leader election. */ private final Candidate candidate; private final Object lifecycleMonitor = new Object(); /** * Curator utility for selecting leaders. */ private volatile LeaderSelector leaderSelector; /** * @see SmartLifecycle */ private volatile boolean autoStartup = true; /** * @see SmartLifecycle which is an extension of org.springframework.context.Phased */ private volatile int phase; /** * Flag that indicates whether the leadership election for * this {@link #candidate} is running. */ private volatile boolean running; /** Base path in a zookeeper */ private final String namespace; /** Leader event publisher if set */ private volatile LeaderEventPublisher leaderEventPublisher; /** * Construct a {@link LeaderInitiator}. * * @param client Curator client * @param candidate leadership election candidate */ public LeaderInitiator(CuratorFramework client, Candidate candidate) { this(client, candidate, DEFAULT_NAMESPACE); } /** * Construct a {@link LeaderInitiator}. * * @param client Curator client * @param candidate leadership election candidate * @param namespace namespace base path in zookeeper */ public LeaderInitiator(CuratorFramework client, Candidate candidate, String namespace) { this.client = client; this.candidate = candidate; this.namespace = namespace; } /** * @return true if leadership election for this {@link #candidate} is running */ @Override public boolean isRunning() { return this.running; } @Override public int getPhase() { return this.phase; } /** * @param phase the phase * @see SmartLifecycle */ public void setPhase(int phase) { this.phase = phase; } @Override public boolean isAutoStartup() { return this.autoStartup; } /** * @param autoStartup true to start automatically * @see SmartLifecycle */ public void setAutoStartup(boolean autoStartup) { this.autoStartup = autoStartup; } /** * Start the registration of the {@link #candidate} for leader election. */ @Override public void start() { synchronized (this.lifecycleMonitor) { if (!this.running) { if (this.client.getState() != CuratorFrameworkState.STARTED) { // we want to do curator start here because it needs to // be started before leader selector and it gets a little // complicated to control ordering via beans so that // curator is fully started. this.client.start(); } this.leaderSelector = new LeaderSelector(this.client, buildLeaderPath(), new LeaderListener()); this.leaderSelector.setId(this.candidate.getId()); this.leaderSelector.autoRequeue(); this.leaderSelector.start(); this.running = true; logger.debug("Started LeaderInitiator"); } } } /** * Stop the registration of the {@link #candidate} for leader election. * If the candidate is currently leader, its leadership will be revoked. */ @Override public void stop() { synchronized (this.lifecycleMonitor) { if (this.running) { this.leaderSelector.close(); this.running = false; logger.debug("Stopped LeaderInitiator"); } } } @Override public void stop(Runnable runnable) { stop(); runnable.run(); } /** * Sets the {@link LeaderEventPublisher}. * * @param leaderEventPublisher the event publisher */ public void setLeaderEventPublisher(LeaderEventPublisher leaderEventPublisher) { this.leaderEventPublisher = leaderEventPublisher; } /** * The context of the initiator or null if not running. * @return the context (or null if not running) * @since 5.0 */ public Context getContext() { if (this.leaderSelector == null) { return NULL_CONTEXT; } return this.context; } /** * @return the ZooKeeper path used for leadership election by Curator */ private String buildLeaderPath() { String ns = StringUtils.hasText(this.namespace) ? this.namespace : DEFAULT_NAMESPACE; if (!ns.startsWith("/")) { ns = "/" + ns; } if (!ns.endsWith("/")) { ns = ns + "/"; } return ns + this.candidate.getRole(); } /** * Implementation of Curator leadership election listener. */ protected class LeaderListener extends LeaderSelectorListenerAdapter { @Override public void takeLeadership(CuratorFramework framework) throws Exception { try { LeaderInitiator.this.candidate.onGranted(LeaderInitiator.this.context); if (LeaderInitiator.this.leaderEventPublisher != null) { try { LeaderInitiator.this.leaderEventPublisher.publishOnGranted(LeaderInitiator.this, LeaderInitiator.this.context, LeaderInitiator.this.candidate.getRole()); } catch (Exception e) { logger.warn("Error publishing OnGranted event.", e); } } // when this method exits, the leadership will be revoked; // therefore this thread needs to be held up until the // candidate is no longer leader Thread.sleep(Long.MAX_VALUE); } catch (InterruptedException e) { // InterruptedException, like any other runtime exception, // is handled by the finally block below. No need to // reset the interrupt flag as the interrupt is handled. } finally { LeaderInitiator.this.candidate.onRevoked(LeaderInitiator.this.context); if (LeaderInitiator.this.leaderEventPublisher != null) { try { LeaderInitiator.this.leaderEventPublisher.publishOnRevoked(LeaderInitiator.this, LeaderInitiator.this.context, LeaderInitiator.this.candidate.getRole()); } catch (Exception e) { logger.warn("Error publishing OnRevoked event.", e); } } } } } /** * Implementation of leadership context backed by Curator. */ private class CuratorContext implements Context { CuratorContext() { super(); } @Override public boolean isLeader() { return LeaderInitiator.this.leaderSelector.hasLeadership(); } @Override public void yield() { LeaderInitiator.this.leaderSelector.interruptLeadership(); } @Override public String toString() { return "CuratorContext{role=" + LeaderInitiator.this.candidate.getRole() + ", id=" + LeaderInitiator.this.candidate.getId() + ", isLeader=" + isLeader() + "}"; } } }