Java tutorial
/** * Copyright 2014 Comcast Cable Communications Management, LLC * * 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.comcast.viper.flume2storm.location; import java.io.Serializable; import java.util.ArrayList; import java.util.Collection; import java.util.List; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import org.apache.zookeeper.CreateMode; import org.apache.zookeeper.KeeperException; import org.apache.zookeeper.WatchedEvent; import org.apache.zookeeper.Watcher; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import com.comcast.viper.flume2storm.utility.test.TestCondition; import com.comcast.viper.flume2storm.utility.test.TestUtils; import com.comcast.viper.flume2storm.zookeeper.ZkClient; import com.comcast.viper.flume2storm.zookeeper.ZkClientListener; import com.comcast.viper.flume2storm.zookeeper.ZkNodeCreationArg; import com.comcast.viper.flume2storm.zookeeper.ZkOperation; import com.comcast.viper.flume2storm.zookeeper.ZkUtilies; import com.google.common.base.Preconditions; /** * An implementation of LocationService that uses ZooKeeper for coordination: * the ServiceProviders advertise their presence by maintaining an ephemeral * znode. * * @param <SP> * The Service Provider class */ public class DynamicLocationService<SP extends ServiceProvider<?>> extends AbstractLocationService<SP> { // TODO It would be nice to have a utility that connects using the dynamic // location service and expose the service providers available protected static final Logger LOG = LoggerFactory.getLogger(DynamicLocationService.class); private static final String SNODE_BASE_NAME = "server"; protected final ZkClient zkClient; // ZK's path for that service: $basePath/$serviceName protected final String servicePath; // Local registration private final Map<SP, String> registrations; private final ServiceProviderSerialization<SP> serviceProviderSerialization; /** * Constructor for {@link DynamicLocationService} * * @param config * The {@link DynamicLocationService} configuration * @param ser * The {@link ServiceProvider} serialization */ public DynamicLocationService(final DynamicLocationServiceConfiguration config, final ServiceProviderSerialization<SP> ser) { this.serviceProviderSerialization = ser; zkClient = new ZkClient(new ZkListener()); zkClient.configure(config); servicePath = ZkUtilies.buildZkPath(config.getBasePath(), config.getServiceName()); registrations = new ConcurrentHashMap<SP, String>(); LOG.debug("Created DynamicLocationService with: {}", config); } /** * Connects ZooKeeper and initializes the {@link DynamicLocationService} * * @see com.comcast.viper.flume2storm.location.LocationService#start() */ @Override public boolean start() { LOG.debug("Starting..."); if (!zkClient.start()) return false; // TODO use configuration to set a max timeout return waitReady(); } /** * Disconnects ZooKeeper and terminates the {@link DynamicLocationService} * * @see com.comcast.viper.flume2storm.location.LocationService#stop() */ @Override public boolean stop() { LOG.debug("Stopping..."); return zkClient.stop(); } /** * @return True if connected to Zookeeper */ public boolean isConnected() { return zkClient.getState().isConnected(); } private class ZkClientReadyCondition implements TestCondition { protected ZkClientReadyCondition() { super(); } /** * @see com.comcast.viper.flume2storm.utility.test.TestCondition#evaluate() */ @Override public boolean evaluate() { return zkClient.getState().isSetup(); } } /** * Sleeps until the library is ready to proceed (i.e. connection established, * setup completed, ...) * * @param timeout * The maximum amount of time to wait (in milliseconds) * @return True if the {@link DynamicLocationService} is ready, false if the * operation timed out */ protected boolean waitReady(final int timeout) { try { return TestUtils.waitFor(new ZkClientReadyCondition(), timeout, 100); } catch (Exception e) { return false; } } /** * Sleeps until the library is ready to proceed (i.e. connection established, * setup completed, ...) * * @throws InterruptedException * If the thread is interrupted while waiting */ protected boolean waitReady() { return waitReady(Integer.MAX_VALUE); } /** * @see com.comcast.viper.flume2storm.location.LocationService#register(com.comcast.viper.flume2storm.location.ServiceProvider) */ public void register(SP serviceProvider) { Preconditions.checkNotNull(serviceProvider); // TODO Perhaps put a request on the queue to make sure this happens // when connected if (registrations.containsKey(serviceProvider)) { LOG.warn("ServiceProvider {} already registered", serviceProvider); return; } if (!isConnected()) { LOG.warn("Not connected to ZooKeeper"); return; } LOG.debug("Registering service..."); try { // TODO improve disconnection performances by using a std // ephemeral node and using UUID of the ServiceInstance final byte[] bytes = serviceProviderSerialization.serialize(serviceProvider); final String p = ZkUtilies.buildZkPath(servicePath, SNODE_BASE_NAME); String lastNodeName = new ZkOperation(zkClient, p).createNode( new ZkNodeCreationArg().setCreateMode(CreateMode.EPHEMERAL_SEQUENTIAL).setData(bytes)); LOG.debug("Created ephemeral node: {}", lastNodeName); registrations.put(serviceProvider, lastNodeName); } catch (final Exception e) { LOG.error("Failed to register server instance: " + serviceProvider, e); } } /** * @see com.comcast.viper.flume2storm.location.LocationService#unregister(com.comcast.viper.flume2storm.location.ServiceProvider) */ public void unregister(SP serviceProvider) { Preconditions.checkNotNull(serviceProvider); if (!isConnected()) { LOG.warn("Not connected to ZooKeeper"); return; } if (!registrations.containsKey(serviceProvider)) { LOG.warn("ServiceProvider {} not registered locally", serviceProvider); return; } try { new ZkOperation(zkClient, registrations.remove(serviceProvider)).deleteNode(); } catch (Exception e) { LOG.error("Failed to unregister server instance: " + serviceProvider, e); } } /** * @see com.comcast.viper.flume2storm.location.LocationService#getSerialization() */ public ServiceProviderSerialization<SP> getSerialization() { return serviceProviderSerialization; } private class ZkListener implements ZkClientListener, Serializable { private static final long serialVersionUID = 4468828482344119321L; protected ZkListener() { super(); } /** * @see com.comcast.viper.flume2storm.zookeeper.ZkClientListener#initialize() */ @Override public void initialize() { // Making directory structure try { LOG.debug("Enforcing base path ({}) existence...", servicePath); new ZkOperation(zkClient, servicePath).createNode( new ZkNodeCreationArg().setCreateHierarchy(true).setCreateMode(CreateMode.PERSISTENT)); getServiceInstances(); } catch (final Exception e) { LOG.error("Failed to setup ZooKeeper connection", e); } // Registering // TODO if any? } /** * @see com.comcast.viper.flume2storm.zookeeper.ZkClientListener#terminate() */ @Override public void terminate() { // Nothing to do } /** * @see com.comcast.viper.flume2storm.zookeeper.ZkClientListener#onConnection() */ @Override public void onConnection() { // Nothing to do } /** * @see com.comcast.viper.flume2storm.zookeeper.ZkClientListener#onDisconnection() */ @Override public void onDisconnection() { // Nothing to do } } /** * Updates the list of active {@link ServiceProvider} servers, and sets a * watch so that we get notified if the list changes */ protected synchronized void getServiceInstances() { if (!zkClient.getState().isConnected()) { return; } final Watcher watcher = new Watcher() { @Override public void process(final WatchedEvent event) { LOG.debug("Service node watch triggered with event: {}", event); getServiceInstances(); } }; try { final List<String> res = new ZkOperation(zkClient, servicePath).getChildren(watcher); final Collection<SP> newList = new ArrayList<SP>(); for (final String child : res) { final String childPath = ZkUtilies.buildZkPath(servicePath, child); try { final byte[] bytes = new ZkOperation(zkClient, childPath).getData(); newList.add(serviceProviderSerialization.deserialize(bytes)); } catch (final KeeperException.NoNodeException nne) { // Programming note: The node was removed been the time we // got the // list and the parsing time... no big deal LOG.debug("znode {} disappear: {}", childPath, nne.getLocalizedMessage()); } catch (final Exception e) { LOG.warn("Failed to deserialize znode " + childPath, e); } } serviceProviderManager.set(newList); } catch (final Exception e) { if (zkClient.getState().isConnected()) { LOG.error("Failed to get service instances", e); } // Otherwise, we might have a clue why this is failing! :) } } }