cn.lhfei.zookeeper.ch01.MasterShipWorker.java Source code

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Here is the source code for cn.lhfei.zookeeper.ch01.MasterShipWorker.java

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/*
 * Copyright 2010-2011 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 cn.lhfei.zookeeper.ch01;

import java.io.IOException;
import java.util.Random;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.ConnectionLossException;
import org.apache.zookeeper.KeeperException.NoNodeException;
import org.apache.zookeeper.KeeperException.NodeExistsException;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @version 1.0.0
 *
 * @author Hefei Li
 *
 * @since Feb 26, 2016
 */
public class MasterShipWorker implements Watcher {

    private static final Logger log = LoggerFactory.getLogger(MasterShipWorker.class);

    private Random random = new Random(this.hashCode());
    private ZooKeeper zk;
    private String hostPort;
    private String serverId = Integer.toHexString(random.nextInt());
    private static boolean isLeader = false;

    public MasterShipWorker(String hostPort) {
        this.hostPort = hostPort;
    }

    void startZK() {
        try {
            zk = new ZooKeeper(hostPort, 15000, this);
        } catch (IOException e) {
            log.error(e.getMessage(), e);
        }
    }

    /**
     * Closes the ZooKeeper session.
     *
     * @throws IOException
     */
    void stopZK() throws InterruptedException, IOException {
        zk.close();
    }

    // returns true if there is a master
    boolean checkMaster() throws KeeperException, InterruptedException {
        while (true) {
            try {
                Stat stat = new Stat();
                byte data[] = zk.getData("/master", false, stat);
                isLeader = new String(data).equals(serverId);
                return true;
            } catch (NoNodeException e) {
                // no master, so try create again
                log.error(e.getMessage(), e);

                return false;
            } catch (ConnectionLossException e) {
                log.error(e.getMessage(), e);
            }
        }
    }

    void runForMaster() throws InterruptedException, KeeperException {
        while (true) {
            try {
                zk.create("/master", serverId.getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
                isLeader = true;
                break;
            } catch (NodeExistsException e) {
                isLeader = false;
                break;
            } catch (ConnectionLossException e) {
            }
            if (checkMaster())
                break;
        }
    }

    @Override
    public void process(WatchedEvent e) {
        log.info(e.toString());
    }

    public static void main(String[] args) throws InterruptedException, IOException, KeeperException {
        MasterShipWorker m = new MasterShipWorker("basic.internal.hadoop.10-148-10-81.scloud.letv.com:2181");
        m.startZK();

        m.runForMaster();

        if (isLeader) {
            log.info("I'm the leader");
            // wait for a bit
            Thread.sleep(60000);
        } else {
            log.info("Someone else is the leader");
        }
        m.stopZK();
    }

}