zookeeper編程（二）

轉自：http://www.cnblogs.com/zhangchaoyang/articles/3813217.html

ZooKeeper的輪廓

/---root

  |

  \----child1

  |

  \----child2

  |

  \----child3

     |

     \----grandson1

     |

     \----grandson2

採用了簡化的praxos算法來確保zookeeper集羣節點的數據一致性

只要Quorum的成員有一半以上處於正常狀態，就能對外提供服務

任何修改命令都需要leader協調。 在leader的協調過程中，需要3次leader與Follower之間的來回請求響應。並且在此過程中還會涉及事務日誌的記錄，更糟糕的情況是還有take snapshot的操作。因此此過程可能比較耗時。但Zookeeper的通信中最大特點是異步的，如果請求是連續不斷的,Zookeeper的處理是集中處理邏輯，然後批量發送，批量的大小也是有控制的。如果請求量不大，則即刻發送。這樣當負載很大時也能保證很大的吞吐量，時效性也在一定程度上進行了保證。

Zookeeper特性

▪簡單：本質上是一個小型分佈式文件系統，其數據結構就是znode樹，對znode的讀寫是原子的。儘量保證單個znode在1MB一下，通常幾K。

▪可靠：可以運行在一組服務器上，數據在每臺server上都有備份，避免單點失效。

▪快速：數據全部加載到內存中，讀寫比例爲10:1時性能最佳（讀是局部性的，寫需要由leader通知給所有server）。在更新內存中的znode之前會先序列到磁盤，服務重啓後數據可以恢復。

▪鬆耦合：Watcher機制使得各客戶端與服務器的交互變得鬆耦合，每個客戶端無需知曉其他客戶端的存在，就可以和其他客戶端進行數據交互。

服務端配置

#  心跳間隔時間

tickTime=2000 

# 最小SessionTimeou 

minSessionTimeout=4000

# 最大SessionTimeou

maxSessionTimeout=100000

# 允許 follower （相對於 leader 而言的“客戶端”）連接並同步到 leader 的初始化連接時間爲tickTime的多少倍，超過這個時間則連接失敗

initLimit=10

# eader 與 follower 之間發送消息，請求和應答時間長度。如果 follower 在設置的時間內不能與 leader 進行通信，那麼此 follower 將被丟棄

syncLimit=5

# 客戶端連接最大數

maxClientCnxns=30

客戶端配置

ZooKeeper  zkp = new ZooKeeper("192.168.119.96:2181,   192.168.119.97:2181 , 192.168.119.98:2181 /app/learn", TIMEOUT,null));

▪client連接zookeeper連接的時候，最好指定>=2個zookeeper服務器地址,這樣當一個zookeeper當掉後，client會自動failover到其它的連接。這時候default watcher會先收到一個Disconnected事件，連接的新的Zookeeper服務器後會收到一個SyncConnected事件。這種情況下session建立的臨時節點不會丟失，所以程序一般不需要對這點做什麼特別的工作。

▪如果你指定的zookeeper中有leader,它好像會直接連接到leader，如果是global集羣或多機房集羣，建議只指定本機房的zooleeper。

▪如果client連接指定的所有zookeeper server都當掉了，先還是會收到一個Disconnected事件，然後臨時節點消失，啓動zookeeper server後會收到Expired事件。

import java.io.IOException;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.data.Stat;

/**
 * 
 * @description ZooKeeper基本讀寫操作演示類
 * @author zhangchaoyang
 * @date 2014-6-22
 */
public class SimplestDemo {
    private static final int TIMEOUT = 3000;

    public static void main(String[] args) throws IOException, KeeperException,
            InterruptedException {
        // Client向zookeeper發送連接請求
        ZooKeeper zkp = new ZooKeeper("192.168.119.96:2181/app/learn", // 指定zookeeper
                                                                        // server的IP、端口列表（當client連接不上server時會按照此列表嘗試連接下一臺server），以及默認的根目錄
                TIMEOUT,// Session Timeout
                null// 是否設置監聽器
        );

        zkp.create("/znodename", // 節點名稱
                "znodedata".getBytes(), // 節點上的數據
                Ids.OPEN_ACL_UNSAFE,// ACL
                CreateMode.EPHEMERAL// 節點類型，有三種：PERSISTENT、EPHEMERAL、SEQUENTIAL。EPHEMERAL節點不允許有子節點
        );

        Stat stat = zkp.exists("/znodename",// 節點名，如果節點不存在，則exists()返回null
                false// 是否設置監聽器
                );
        if (zkp.exists("/znodename", false) != null) {
            System.out.println("znodename exists now.");
        }

        // 修改節點上存儲的數據，需要提供version，version設爲-1表示強制修改
        zkp.setData("/znodename", "newdata".getBytes(), stat.getVersion());

        // 讀取節點上的數據
        String data = new String(zkp.getData("/znodename", false, stat));
        System.out.println(data);

        // client端主動斷開連接
        zkp.close();
    }
}

Session

▪Zookeeper爲每個client分配一個Session，Session數據在每臺zookeeper節點上都有備份。

▪Server每隔tickTime向Client發送一個心跳。

▪session失效有兩種可能性：client主動調用close() ；Server和Client 長時間（時間大於TIMEOUT ）失去聯繫。

▪Session失效後與Session關聯的數據（比如EPHEMERAL節點，Watcher）會從內存中移除。

▪如果Server和Client只是短暫（時間小於TIMEOUT ）地失去聯繫，則Session不會失效，Client再次請求Zookeeper時會把上次的SessionID帶上。

▪Server和Client失去聯繫有兩種情況：Server宕機（Zookeeper集羣會讓Client與另一臺Server建立連接）；網絡異常。

import java.io.IOException;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.ConnectionLossException;
import org.apache.zookeeper.KeeperException.SessionExpiredException;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.data.Stat;
import org.apache.zookeeper.ZooKeeper;

/**
 * 
 * @description Zookeeper Session演示類
 * @author zhangchaoyang
 * @date 2014-6-22
 */
public class SessionDemo {
    /**
     * zoo.cfg中的配置：
     * 
     * <pre>
     * tickTime=2000
     * minSessionTimeout=4000（至少是tickTime的2倍）
     * maxSessionTimeout=40000（最大是tickTime的20倍）
     * </pre>
     * 
     * 如果客戶端建立連接時指定的TIMEOUT不在[minSessionTimeout,maxSessionTimeout]區間內，
     * 服務端會強制把它修改到該區間內
     */
    private static final int TIMEOUT = 40000; // Session
                                                // Timeout設爲40秒，因爲心跳週期爲2秒，所以如果server向client連續發送20個心跳都收不到迴應，則Session過期失效
    private static ZooKeeper zkp = null;

    private static void connect() throws IOException {
        zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT, null);
    }

    private static void createNode() throws KeeperException,
            InterruptedException {
        if (zkp != null) {
            zkp.create("/znodename", "znodedata".getBytes(),
                    Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        }
    }

    private static String getData() throws KeeperException,
            InterruptedException {
        if (zkp != null) {
            Stat stat = zkp.exists("/znodename", false);
            return new String(zkp.getData("/znodename", false, stat));
        }
        return null;
    }

    private static void disconnect() throws InterruptedException {
        if (zkp != null) {
            zkp.close();
        }
    }

    /**
     * 休息，在此期間我們有三種選擇：<br>
     * <ol>
     * <li>永久性斷開網絡連接
     * <li>斷開網絡連接一段時間timespan後再連上，其中timespan<{@code TIMEOUT}
     * <li>斷開網絡連接一段時間timespan後再連上，其中timespan>{@code TIMEOUT}
     * </ol>
     */
    private static void sleepForNetworkDisturbances() {
        try {
            Thread.sleep(2 * TIMEOUT);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        try {
            connect();
        } catch (IOException e) {
            System.err
                    .println("Can't create zookeeper client, please check the network.");
        }
        System.out.println("Session build.");

        try {
            createNode();
        } catch (Exception e) {
            System.err.println("Create znode failed.");
        }
        System.out.println("znode created.");

        sleepForNetworkDisturbances();

        try {
            String data = getData();
            if (data != null) {
                // 在“休息”期間做了第2件事情，Sesion沒有過期，EPHEMERAL節點依然存在
                System.out.println("data=" + data);
            }
        } catch (KeeperException e) {
            e.printStackTrace();
            // 在“休息”期間做了第1件事情
            if (e instanceof ConnectionLossException) {
                System.err
                        .println("Oops, network is disconnected. Retry getData().");
                // 如果session沒有失效，而僅僅是網絡異常，則可以重新嘗試獲取數據，可能在重試時網絡已經正常了
                try {
                    Thread.sleep(1000);
                    String data = getData();
                    if (data != null) {
                        System.out.println("data=" + data);
                    } else {
                        System.out.println("can't get data.");
                    }
                } catch (Exception e1) {
                    e1.printStackTrace();
                }
            }
            // 在“休息”期間做了第3件事情，則session會過期
            else if (e instanceof SessionExpiredException) {
                System.err
                        .println("Session Expired, client will reconnect and create znode again.");
                // 當發再Session Expired時，必須重新建立連接，即new一個ZooKeeper
                try {
                    connect();
                    createNode();
                    String data = getData();
                    if (data != null) {
                        System.out.println("data=" + data);
                    } else {
                        System.out.println("can't get data.");
                    }
                } catch (Exception e1) {
                    e1.printStackTrace();
                }
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        try {
            disconnect();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("Client disconnected.");
    }
}

Watcher

▪可以註冊watcher的方法：getData、exists、getChildren。

▪可以觸發watcher的方法：create、delete、setData。連接斷開的情況下觸發的watcher會丟失。

▪一個Watcher實例是一個回調函數，被回調一次後就被移除了。如果還需要關注數據的變化，需要再次註冊watcher。

▪New ZooKeeper時註冊的watcher叫default watcher，它不是一次性的，只對client的連接狀態變化作出反應。

什麼樣的操作會產生什麼類型的事件：

	event For “/path”	event For “/path/child”
create(“/path”)	EventType.NodeCreated	--
delete(“/path”)	EventType.NodeDeleted	--
setData(“/path”)	EventType.NodeDataChanged	--
create(“/path/child”)	EventType.NodeChildrenChanged	EventType.NodeCreated
delete(“/path/child”)	EventType.NodeChildrenChanged	EventType.NodeDeleted
setData(“/path/child”)	--	EventType.NodeDataChanged

 什麼操作會觸發EventType.None？

事件類型與watcher的對應關係：

event For “/path”	Default Watcher	exists (“/path”)	getData (“/path”)	getChildren (“/path”)
EventType.None	√	√	√	√
EventType.NodeCreated		√	√
EventType.NodeDeleted		√	√
EventType.NodeDataChanged		√	√
EventType.NodeChildrenChanged				√

操作與watcher的對應關係：

 

	"/path"			"/path/child"
	exists	getData	getChildren	exists	getData	getChildren
create(“/path”)	√	√
delete(“/path”)	√	√	√
setData(“/path”)	√	√
create(“/path/child”)			√	√	√
delete(“/path/child”)			√	√	√	√
setData(“/path/child”)				√	√

import java.io.IOException;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.data.Stat;

/**
 * 
 * @description Zookeeper Watcher演示類
 * @author zhangchaoyang
 * @date 2014-6-22
 */
public class WatcherDemo {
    private static ZooKeeper zkp = null;
    private static final int TIMEOUT = 6000;

    private static Watcher getWatcher(final String msg) {
        return new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                System.out.println(msg + "上的監聽被觸發\t事件類型" + event.getType()
                        + "\t發生變化的節點" + event.getPath());
            }
        };
    }

    public static void main(String[] args) throws IOException, KeeperException,
            InterruptedException {
        System.out.println("--------------1----------------");
        zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT,
                getWatcher("CONNECT"));
        Thread.sleep(1000);
        
        System.out.println("--------------2----------------");
        zkp.create("/znodename", "znodedata".getBytes(), Ids.OPEN_ACL_UNSAFE,
                CreateMode.PERSISTENT);
        zkp.create("/znodename/childnode", new byte[0], Ids.OPEN_ACL_UNSAFE,
                CreateMode.PERSISTENT);

        Stat stat = zkp.exists("/znodename", getWatcher("EXISTS"));
        zkp.getChildren("/", getWatcher("GETCHILDREN"));
        zkp.getData("/znodename", getWatcher("GETDATA"), stat);

        stat = zkp.exists("/znodename/childnode", getWatcher("EXISTS"));
        zkp.getChildren("/znodename", getWatcher("GETCHILDREN"));
        zkp.getData("/znodename/childnode", getWatcher("GETDATA"), stat);

        // zkp.close();
        zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT,
                getWatcher("CONNECT"));
        Thread.sleep(1000);

        System.out.println("--------------3----------------");
        zkp.delete("/znodename/childnode", -1);
        zkp.delete("/znodename", -1);
        zkp.close();
    }
}

 

import java.io.IOException;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.ConnectionLossException;
import org.apache.zookeeper.KeeperException.SessionExpiredException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.EventType;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

/**
 * 
 * @description 自定義持久性的zookeeper watcher
 * @author zhangchaoyang
 * @date 2014-6-22
 */
public class PersistWatcher {

    private static final int TIMEOUT = 6000;
    private static final String znode = "/globalconfnode";
    private static String globalConfData = "";

    private static Watcher getConnectWatcher() {
        return new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                if (event.getType().equals(EventType.None)) {
                    System.out.println("連接狀態發生變化。");
                }
            }
        };
    }

    private static Watcher getExistsWatcher(final ZooKeeper zkp) {
        return new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                try {
                    if (event.getType().equals(EventType.NodeDataChanged)
                            || event.getType().equals(EventType.NodeCreated)) {
                        // 節點被創建或修改時更新緩存中的值
                        Stat stat = zkp.exists(znode, this);// 再次註冊監聽
                        String data = new String(
                                zkp.getData(znode, false, stat));
                        globalConfData = data;
                    } else if (event.getType().equals(EventType.NodeDeleted)) {
                        // 節點被刪除時報警
                        System.out
                                .println("global configuration node have been deleted!");
                        try {
                            // 再次註冊監聽
                            zkp.exists(znode, this);
                        } catch (KeeperException e) {
                            if (e instanceof ConnectionLossException) {
                                System.out.println("連接已斷開。");
                            }
                        }
                    }
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
    }

    public static void main(String[] args) {
        try {
            ZooKeeper zkp = new ZooKeeper("192.168.119.96:2181/app/learn",
                    TIMEOUT, 
                    getConnectWatcher());
            zkp.exists(znode, getExistsWatcher(zkp));
            zkp.create(znode, "config_value".getBytes(), Ids.OPEN_ACL_UNSAFE,
                    CreateMode.EPHEMERAL);

            Thread.sleep(500);// 修改節點後必須sleep，等待watcher回調完成
            System.out.println(globalConfData);

            for (int i = 0; i < 4; i++) {
                zkp.setData(znode, ("config_value" + i).getBytes(), -1);
                Thread.sleep(500);// 修改節點後必須sleep，等待watcher回調完成
                System.out.println(globalConfData);
            }

            zkp.close();// EPHEMERAL節點會被刪除，但Session並不會馬上失效(只不過ConnectionLoss了)，所以還是會觸發watcher

            try {
                // 此時Session已失效
                zkp.exists(znode, false);
            } catch (KeeperException e) {
                if (e instanceof SessionExpiredException)
                    System.out.println("Session已失效。");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

ACL

▪每個節點有單獨的ACL，子節點不能繼承父節點的ACL

▪ACL有三個維度：schema,id,permision

▪Schema有7種：

▪world: 它下面只有一個id, 叫anyone

▪auth: 它不需要id

▪digest: 它對應的id爲username:BASE64(SHA1(password))

▪ip: 它對應的id爲客戶機的IP地址，設置的時候可以設置一個ip段，比如ip:192.168.1.0/16, 表示匹配前16個bit的IP段

▪super: 在這種scheme情況下，對應的id擁有超級權限

▪sasl: sasl的對應的id，是一個通過了kerberos認證的用戶id

▪Permission有5種:

▪CREATE(c),DELETE(d),READ(r),WRITE(w),ADMIN(a) 

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.KeeperException.NoAuthException;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;

/**
 * 
 * @description Zookeeper ACL演示類
 * @author zhangchaoyang
 * @date 2014-6-22
 */
public class AclDemo {
    private static final int TIMEOUT = 6000;

    public static void main(String[] args) throws IOException, KeeperException,
            InterruptedException {
        ZooKeeper zkp = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT,
                null);

        String schema = "digest";// schema類型有：world,auth,digest,ip,super
        String auth = "username:password";
        zkp.addAuthInfo(schema, auth.getBytes());

        List<ACL> acls = new ArrayList<ACL>();
        for (ACL id : Ids.CREATOR_ALL_ACL) {
            acls.add(id);
        }
        zkp.create("/znodename", "znodedata".getBytes(), acls,
                CreateMode.PERSISTENT);

        ZooKeeper zoo = null;
        try {
            zoo = new ZooKeeper("192.168.119.96:2181/app/learn", TIMEOUT, null);
            System.out.println("採用不合法的認證方式：");
            String badAuthentication = "username:wrongpass";
            zoo.addAuthInfo(schema, badAuthentication.getBytes());
            zoo.getData("/znodename", null, null);
        } catch (KeeperException e) {
            if (e instanceof NoAuthException) {
                System.out.println("認證失敗：" + e.getMessage());
            }
            System.out.println("採用合法的認證方式：");
            zoo.addAuthInfo(schema, auth.getBytes());
            String data = new String(zoo.getData("/znodename", null, null));
            if (data != null) {
                System.out.println("認證成功：data=" + data);
            }
        } finally {
            if (zoo != null && zoo.getState().isAlive()) {
                zoo.close();
            }
        }

        zkp.delete("/znodename", -1);
        zkp.close();
    }
}

開源工具menagerie

▪基於ZooKeeper實現了分佈式的：

▪ReentrantZkLock

▪ReentrantZkReadWriteLock

▪Semaphore

▪CyclicBarrier

▪CountDownLatch

▪BlockingQueue

▪HashMap

▪ListSet

import java.io.IOException;
import java.util.Date;
import java.util.List;
import java.util.concurrent.CountDownLatch;

import org.apache.log4j.Logger;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.ZooKeeper.States;

/**
 * 
 * @description 使用ZooKeeper實現分佈式鎖
 * @author zhangchaoyang
 * @date 2014-6-22
 */
public class ZooKeeperLock {

    private static Logger logger = Logger.getLogger(ZooKeeperLock.class);

    private static ZooKeeper zk = null;
    private static final int TIMEOUT = 1000 * 60;
    private static String connStr = null;

    public static void setServerPath(String path) {
        connStr = path + "/app/bqas/lock";
        logger.info("ZooKeeperLock zookeeper node:" + connStr);
    }

    public static boolean getLock(String lockname) throws KeeperException,
            InterruptedException, IOException {
        connect(connStr, TIMEOUT);
        if (lockname.contains("-")) {
            throw new RuntimeException("鎖名稱不能包含'-'");
        }
        boolean lock = false;
        String path = zk.create("/" + lockname + "-", new byte[0],
                Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        int selfIndex = getIndex(path);
        List<String> children = zk.getChildren("/", false);
        int min = getMinIndex(children);
        if (min == selfIndex) {
            lock = true;
        }

        return lock;
    }

    public static void releaseLock(String lockname)
            throws InterruptedException, KeeperException {
        disconnect();
    }

    private static int getIndex(String str) {
        int index = -1;
        int pos = str.lastIndexOf("-");
        if (pos >= 0) {
            try {
                index = Integer.parseInt(str.substring(pos + 1));
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
        }
        return index;
    }

    private static int getMinIndex(List<String> list) {
        int min = Integer.MAX_VALUE;
        for (String ele : list) {
            int index = getIndex(ele);
            if (index < 0) {
                throw new RuntimeException("SEQUENTIAL節點名中不包含數字：" + ele);
            }
            if (index < min) {
                min = index;
            }
        }
        return min;
    }

    private static void waitUntilConnected(CountDownLatch connectedLatch) {
        if (States.CONNECTING == zk.getState()) {
            try {
                connectedLatch.await();
            } catch (InterruptedException e) {
                throw new IllegalStateException(e);
            }
        }
    }

    public static boolean connect(String hostPath, int sessionTimeout) {
        if (zk == null || zk.getState() == States.CLOSED) {
            try {
                CountDownLatch connectedLatch = new CountDownLatch(1);
                Watcher watcher = new ConnectedWatcher(connectedLatch);
                zk = new ZooKeeper(hostPath, sessionTimeout, watcher);
                waitUntilConnected(connectedLatch);
            } catch (Exception e) {
                logger.error("Connect to Zookeeper failed:", e);
                return false;
            }
        }
        return true;
    }

    public static boolean disconnect() {
        if (zk != null) {
            if (States.CLOSED != zk.getState()) {
                try {
                    zk.close();
                } catch (InterruptedException e) {
                    logger.error("Disconnect from Zookeeper failed:", e);
                    return false;
                }
            }
        }
        return true;
    }

    static class ConnectedWatcher implements Watcher {

        private CountDownLatch connectedLatch;

        ConnectedWatcher(CountDownLatch connectedLatch) {
            this.connectedLatch = connectedLatch;
        }

        @Override
        public void process(WatchedEvent event) {
            // 事件狀態爲SyncConnected時，說明與服務端的連接已建立好
            if (event.getState() == KeeperState.SyncConnected) {
                connectedLatch.countDown();
            }
        }
    }

    public static void main(String[] args) {
        String lockname = "writeHitCount2DBlock";
        System.out.println("begin to run.");
        ZooKeeperLock.setServerPath("192.168.119.96:2181");
        try {
            boolean havelock = ZooKeeperLock.getLock(lockname);
            if (havelock) {
                Date date = new Date();
                System.out
                        .println("I got the lock,and I will write DB!" + date);
                Thread.sleep(1000);// 休息一段時間之後再釋放鎖
            }
            System.out.println("Job done, I will release the lock.");
            ZooKeeperLock.releaseLock(lockname);
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}