Java tutorial
// ================================================================================================= // Copyright 2011 Twitter, Inc. // ------------------------------------------------------------------------------------------------- // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this work except in compliance with the License. // You may obtain a copy of the License in the LICENSE file, or 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.twitter.common.zookeeper; import java.util.List; import java.util.logging.Logger; import com.google.common.base.Preconditions; import com.google.common.collect.ImmutableList; import org.apache.zookeeper.CreateMode; import org.apache.zookeeper.KeeperException; import org.apache.zookeeper.ZooDefs.Ids; import org.apache.zookeeper.common.PathUtils; import org.apache.zookeeper.data.ACL; import com.twitter.common.quantity.Amount; import com.twitter.common.quantity.Time; import com.twitter.common.zookeeper.ZooKeeperClient.ZooKeeperConnectionException; /** * Utilities for dealing with zoo keeper. */ public final class ZooKeeperUtils { private static final Logger LOG = Logger.getLogger(ZooKeeperUtils.class.getName()); /** * An appropriate default session timeout for Twitter ZooKeeper clusters. */ public static final Amount<Integer, Time> DEFAULT_ZK_SESSION_TIMEOUT = Amount.of(4, Time.SECONDS); /** * The magic version number that allows any mutation to always succeed regardless of actual * version number. */ public static final int ANY_VERSION = -1; /** * An ACL that gives all permissions any user authenticated or not. */ public static final ImmutableList<ACL> OPEN_ACL_UNSAFE = ImmutableList.copyOf(Ids.OPEN_ACL_UNSAFE); /** * An ACL that gives all permissions to node creators and read permissions only to everyone else. */ public static final ImmutableList<ACL> EVERYONE_READ_CREATOR_ALL = ImmutableList.<ACL>builder() .addAll(Ids.CREATOR_ALL_ACL).addAll(Ids.READ_ACL_UNSAFE).build(); /** * Returns true if the given exception indicates an error that can be resolved by retrying the * operation without modification. * * @param e the exception to check * @return true if the causing operation is strictly retryable */ public static boolean isRetryable(KeeperException e) { Preconditions.checkNotNull(e); switch (e.code()) { case CONNECTIONLOSS: case SESSIONEXPIRED: case SESSIONMOVED: case OPERATIONTIMEOUT: return true; case RUNTIMEINCONSISTENCY: case DATAINCONSISTENCY: case MARSHALLINGERROR: case BADARGUMENTS: case NONODE: case NOAUTH: case BADVERSION: case NOCHILDRENFOREPHEMERALS: case NODEEXISTS: case NOTEMPTY: case INVALIDCALLBACK: case INVALIDACL: case AUTHFAILED: case UNIMPLEMENTED: // These two should not be encountered - they are used internally by ZK to specify ranges case SYSTEMERROR: case APIERROR: case OK: // This is actually an invalid ZK exception code default: return false; } } /** * Ensures the given {@code path} exists in the ZK cluster accessed by {@code zkClient}. If the * path already exists, nothing is done; however if any portion of the path is missing, it will be * created with the given {@code acl} as a persistent zookeeper node. The given {@code path} must * be a valid zookeeper absolute path. * * @param zkClient the client to use to access the ZK cluster * @param acl the acl to use if creating path nodes * @param path the path to ensure exists * @throws ZooKeeperConnectionException if there was a problem accessing the ZK cluster * @throws InterruptedException if we were interrupted attempting to connect to the ZK cluster * @throws KeeperException if there was a problem in ZK */ public static void ensurePath(ZooKeeperClient zkClient, List<ACL> acl, String path) throws ZooKeeperConnectionException, InterruptedException, KeeperException { Preconditions.checkNotNull(zkClient); Preconditions.checkNotNull(path); Preconditions.checkArgument(path.startsWith("/")); ensurePathInternal(zkClient, acl, path); } private static void ensurePathInternal(ZooKeeperClient zkClient, List<ACL> acl, String path) throws ZooKeeperConnectionException, InterruptedException, KeeperException { if (zkClient.get().exists(path, false) == null) { // The current path does not exist; so back up a level and ensure the parent path exists // unless we're already a root-level path. int lastPathIndex = path.lastIndexOf('/'); if (lastPathIndex > 0) { ensurePathInternal(zkClient, acl, path.substring(0, lastPathIndex)); } // We've ensured our parent path (if any) exists so we can proceed to create our path. try { zkClient.get().create(path, null, acl, CreateMode.PERSISTENT); } catch (KeeperException.NodeExistsException e) { // This ensures we don't die if a race condition was met between checking existence and // trying to create the node. LOG.info("Node existed when trying to ensure path " + path + ", somebody beat us to it?"); } } } /** * Validate and return a normalized zookeeper path which doesn't contain consecutive slashes and * never ends with a slash (except for root path). * * @param path the path to be normalized * @return normalized path string */ public static String normalizePath(String path) { String normalizedPath = path.replaceAll("//+", "/").replaceFirst("(.+)/$", "$1"); PathUtils.validatePath(normalizedPath); return normalizedPath; } private ZooKeeperUtils() { // utility } }