Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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.apache.accumulo.fate.zookeeper; import java.util.List; import java.util.concurrent.CountDownLatch; import java.util.concurrent.atomic.AtomicInteger; import org.apache.accumulo.fate.zookeeper.ZooUtil.ZooKeeperConnectionInfo; import org.apache.zookeeper.AsyncCallback.VoidCallback; import org.apache.zookeeper.KeeperException; import org.apache.zookeeper.KeeperException.Code; import org.apache.zookeeper.Watcher; import org.apache.zookeeper.ZooKeeper; import org.apache.zookeeper.data.ACL; import org.apache.zookeeper.data.Stat; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class ZooReader implements IZooReader { private static final Logger log = LoggerFactory.getLogger(ZooReader.class); protected String keepers; protected int timeout; private final RetryFactory retryFactory; private final ZooKeeperConnectionInfo info; protected ZooKeeper getSession(String keepers, int timeout, String scheme, byte[] auth) { return ZooSession.getSession(keepers, timeout, scheme, auth); } protected ZooKeeper getZooKeeper() { return getSession(keepers, timeout, null, null); } protected RetryFactory getRetryFactory() { return retryFactory; } protected void retryOrThrow(Retry retry, KeeperException e) throws KeeperException { log.warn("Saw (possibly) transient exception communicating with ZooKeeper", e); if (retry.canRetry()) { retry.useRetry(); return; } log.error( "Retry attempts (" + retry.retriesCompleted() + ") exceeded trying to communicate with ZooKeeper"); throw e; } @Override public byte[] getData(String zPath, Stat stat) throws KeeperException, InterruptedException { return getData(zPath, false, stat); } @Override public byte[] getData(String zPath, boolean watch, Stat stat) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().getData(zPath, watch, stat); } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public byte[] getData(String zPath, Watcher watcher, Stat stat) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().getData(zPath, watcher, stat); } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public Stat getStatus(String zPath) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().exists(zPath, false); } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public Stat getStatus(String zPath, Watcher watcher) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().exists(zPath, watcher); } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public List<String> getChildren(String zPath) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().getChildren(zPath, false); } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public List<String> getChildren(String zPath, Watcher watcher) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().getChildren(zPath, watcher); } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public boolean exists(String zPath) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().exists(zPath, false) != null; } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public boolean exists(String zPath, Watcher watcher) throws KeeperException, InterruptedException { final Retry retry = getRetryFactory().create(); while (true) { try { return getZooKeeper().exists(zPath, watcher) != null; } catch (KeeperException e) { final Code code = e.code(); if (code == Code.CONNECTIONLOSS || code == Code.OPERATIONTIMEOUT || code == Code.SESSIONEXPIRED) { retryOrThrow(retry, e); } else { throw e; } } retry.waitForNextAttempt(); } } @Override public void sync(final String path) throws KeeperException, InterruptedException { final AtomicInteger rc = new AtomicInteger(); final CountDownLatch waiter = new CountDownLatch(1); getZooKeeper().sync(path, new VoidCallback() { @Override public void processResult(int code, String arg1, Object arg2) { rc.set(code); waiter.countDown(); } }, null); waiter.await(); Code code = Code.get(rc.get()); if (code != KeeperException.Code.OK) { throw KeeperException.create(code); } } @Override public List<ACL> getACL(String zPath, Stat stat) throws KeeperException, InterruptedException { return ZooUtil.getACL(info, zPath, stat); } public ZooReader(String keepers, int timeout) { this.keepers = keepers; this.timeout = timeout; this.retryFactory = RetryFactory.DEFAULT_INSTANCE; this.info = new ZooKeeperConnectionInfo(keepers, timeout, null, null); } }