推薦：

1.  Curator  實現 

<dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>4.0.1</version>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.zookeeper</groupId>
                    <artifactId>zookeeper</artifactId>
                </exclusion>


            </exclusions>
        </dependency>


        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.13</version>
            <exclusions>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>log4j-over-slf4j</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>slf4j-log4j12</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
 

RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3)
CuratorFramework client = CuratorFrameworkFactory.newClient(zookeeperConnectionString, retryPolicy);
client.start();

InterProcessMutex lock = new InterProcessMutex(client, lockPath);
if ( lock.acquire(maxWait, waitUnit) ) 
{
    try 
    {
        // do some work inside of the critical section here
    }
    finally
    {
        lock.release();
    }
}
 

2. zookeeper 方式

下面就具體使用java和zookeeper實現分散式鎖，操作zookeeper使用的是apache提供的zookeeper的包。

• 通過實現Watch介面，實現process(WatchedEvent event)方法來實施監控，使CountDownLatch來完成監控，在等待鎖的時候使用CountDownLatch來計數，等到後進行countDown，停止等待，繼續執行。
• 以下整體流程基本與上述描述流程一致，只是在監聽的時候使用的是CountDownLatch來監聽前一個節點。

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * Created by liuyang on 2017/4/20.
 */
public class DistributedLock implements Lock, Watcher {
    private ZooKeeper zk = null;
    // 根節點
    private String ROOT_LOCK = "/locks";
    // 競爭的資源
    private String lockName;
    // 等待的前一個鎖
    private String WAIT_LOCK;
    // 當前鎖
    private String CURRENT_LOCK;
    // 計數器
    private CountDownLatch countDownLatch;
    private int sessionTimeout = 30000;
    private List<Exception> exceptionList = new ArrayList<Exception>();

    /**
     * 配置分散式鎖
     * @param config 連線的url
     * @param lockName 競爭資源
     */
    public DistributedLock(String config, String lockName) {
        this.lockName = lockName;
        try {
            // 連線zookeeper
            zk = new ZooKeeper(config, sessionTimeout, this);
            Stat stat = zk.exists(ROOT_LOCK, false);
            if (stat == null) {
                // 如果根節點不存在，則建立根節點
                zk.create(ROOT_LOCK, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
    }

    // 節點監視器
    public void process(WatchedEvent event) {
        if (this.countDownLatch != null) {
            this.countDownLatch.countDown();
        }
    }

    public void lock() {
        if (exceptionList.size() > 0) {
            throw new LockException(exceptionList.get(0));
        }
        try {
            if (this.tryLock()) {
                System.out.println(Thread.currentThread().getName() + " " + lockName + "獲得了鎖");
                return;
            } else {
                // 等待鎖
                waitForLock(WAIT_LOCK, sessionTimeout);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
    }

    public boolean tryLock() {
        try {
            String splitStr = "_lock_";
            if (lockName.contains(splitStr)) {
                throw new LockException("鎖名有誤");
            }
            // 建立臨時有序節點
            CURRENT_LOCK = zk.create(ROOT_LOCK + "/" + lockName + splitStr, new byte[0],
                    ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
            System.out.println(CURRENT_LOCK + " 已經建立");
            // 取所有子節點
            List<String> subNodes = zk.getChildren(ROOT_LOCK, false);
            // 取出所有lockName的鎖
            List<String> lockObjects = new ArrayList<String>();
            for (String node : subNodes) {
                String _node = node.split(splitStr)[0];
                if (_node.equals(lockName)) {
                    lockObjects.add(node);
                }
            }
            Collections.sort(lockObjects);
            System.out.println(Thread.currentThread().getName() + " 的鎖是 " + CURRENT_LOCK);
            // 若當前節點為最小節點，則獲取鎖成功
            if (CURRENT_LOCK.equals(ROOT_LOCK + "/" + lockObjects.get(0))) {
                return true;
            }

            // 若不是最小節點，則找到自己的前一個節點
            String prevNode = CURRENT_LOCK.substring(CURRENT_LOCK.lastIndexOf("/") + 1);
            WAIT_LOCK = lockObjects.get(Collections.binarySearch(lockObjects, prevNode) - 1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
        return false;
    }

    public boolean tryLock(long timeout, TimeUnit unit) {
        try {
            if (this.tryLock()) {
                return true;
            }
            return waitForLock(WAIT_LOCK, timeout);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }

    // 等待鎖
    private boolean waitForLock(String prev, long waitTime) throws KeeperException, InterruptedException {
        Stat stat = zk.exists(ROOT_LOCK + "/" + prev, true);

        if (stat != null) {
            System.out.println(Thread.currentThread().getName() + "等待鎖 " + ROOT_LOCK + "/" + prev);
            this.countDownLatch = new CountDownLatch(1);
            // 計數等待，若等到前一個節點消失，則precess中進行countDown，停止等待，獲取鎖
            this.countDownLatch.await(waitTime, TimeUnit.MILLISECONDS);
            this.countDownLatch = null;
            System.out.println(Thread.currentThread().getName() + " 等到了鎖");
        }
        return true;
    }

    public void unlock() {
        try {
            System.out.println("釋放鎖 " + CURRENT_LOCK);
            zk.delete(CURRENT_LOCK, -1);
            CURRENT_LOCK = null;
            zk.close();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
    }

    public Condition newCondition() {
        return null;
    }

    public void lockInterruptibly() throws InterruptedException {
        this.lock();
    }


    public class LockException extends RuntimeException {
        private static final long serialVersionUID = 1L;
        public LockException(String e){
            super(e);
        }
        public LockException(Exception e){
            super(e);
        }
    }
}
 

測試程式碼：

public class Test {
    static int n = 500;

    public static void secskill() {
        System.out.println(--n);
    }

    public static void main(String[] args) {
        
        Runnable runnable = new Runnable() {
            public void run() {
                DistributedLock lock = null;
                try {
                    lock = new DistributedLock("127.0.0.1:2181", "test1");
                    lock.lock();
                    secskill();
                    System.out.println(Thread.currentThread().getName() + "正在執行");
                } finally {
                    if (lock != null) {
                        lock.unlock();
                    }
                }
            }
        };

        for (int i = 0; i < 10; i++) {
            Thread t = new Thread(runnable);
            t.start();
        }
    }
}

 我的實現方案：

import com.zte.daas.common.exception.GlobalErrException;
import lombok.extern.slf4j.Slf4j;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;

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


@Slf4j
public class ExclusiveLock  implements Watcher {

    private CountDownLatch connectedSemaphore = new CountDownLatch(1);

    private CountDownLatch lockCountDown = new CountDownLatch(1);
    private Date currentDate = null;
    private long timeOut = 0l;
    private ZooKeeper zooKeeper = null;
    private String lockResource = null;
    private LockStatusEnum lockStatusEnum = LockStatusEnum.UN_LOCK;
    public ExclusiveLock(String lockResource,String url) throws IOException, InterruptedException {
        this.lockResource = lockResource;

            zooKeeper = new ZooKeeper(url,5000,this);
            connectedSemaphore.await(5, TimeUnit.SECONDS);

    }

    public boolean createLockNode(){
        try {
            zooKeeper.create(lockResource, "".getBytes(),
                    ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        } catch (KeeperException e) {
            return false;
        } catch (InterruptedException e) {
            return false;
        }
        return true;
    }

    public boolean lock(long timeOut) throws InterruptedException, KeeperException {
        this.currentDate = new Date();
        this.timeOut = timeOut;
        tryLock();
        lockCountDown.await(timeOut,TimeUnit.SECONDS);
        if(LockStatusEnum.LOCKED == lockStatusEnum){
            return true;
        }
        return false;

    }


    public void tryLock() throws InterruptedException, KeeperException {

        //時間超時，返回
        if(new Date().getTime()-currentDate.getTime()>timeOut*1000){
            lockStatusEnum = LockStatusEnum.TRY_LOCK;
            lockCountDown.countDown();
            return;
        }
        if(createLockNode()){
            lockStatusEnum = LockStatusEnum.LOCKED;
            lockCountDown.countDown();
            return;
        }else{
            Stat stat = zooKeeper.exists(lockResource,true);
            if(stat == null){
                tryLock();
            }
        }


        return ;
    }
    public void unLock() throws KeeperException, InterruptedException {
        deleteNode(lockResource);
    }
    public void deleteNode(String path) throws KeeperException, InterruptedException {

        String pathFull = path;
        if(path.equalsIgnoreCase("/zookeeper")){
            return;
        }
        List<String> childNodeList = zooKeeper.getChildren(path,false);
        if(childNodeList.size()>0){
            for(String str :childNodeList){
                if(pathFull.equals("/")){
                    deleteNode(pathFull+str);
                }else {
                    deleteNode(pathFull+"/"+str);
                }

            }
        }else{
            zooKeeper.delete(path,-1);
        }

    }

    public void close() throws InterruptedException {
        if(zooKeeper != null){
            zooKeeper.close();
        }

    }
    //監聽
    @Override
    public void process(WatchedEvent watchedEvent) {

        if(Event.KeeperState.SyncConnected == watchedEvent.getState()){
            if(watchedEvent.getType() == Event.EventType.None){
                connectedSemaphore.countDown();
                return;
            }else if(watchedEvent.getType() == Event.EventType.NodeDeleted){
                log.info("watch----node delete");
                try {
                    tryLock();
                } catch (InterruptedException e) {
                    log.error("trylock:{}",e);
                } catch (KeeperException e) {
                    log.error("trylock:{}",e);
                }

            }
        }
    }

   
}