zookeeper（5）

zookeeper当配置中心

工作中有这样的一个场景: 数据库用户名和密码信息放在一个配置文件中，应用读取该配置文件，配置文件信息放入缓存。
若数据库的用户名和密码改变时候，还需要重新加载缓存，比较麻烦，通过ZooKeeper可以轻松完成，当数据库发生变化时自动完成缓存同步。

设计思路：

1. 连接zookeeper服务器
2. 读取zookeeper中的配置信息，注册watcher监听器，存入本地变量
3. 当zookeeper中的配置信息发生变化时，通过watcher的回调方法捕获数据变化事件
4. 重新获取配置信息

代码如下：

package com.ali.zk;

import java.util.concurrent.CountDownLatch;
import com.ali.zk.ZKConnectionWatcher;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.EventType;
import org.apache.zookeeper.ZooKeeper;
public class MyConfigCenter implements Watcher {
    // zk的连接串
    String IP = "192.168.60.130:2181";
    // 计数器对象
    CountDownLatch countDownLatch = new CountDownLatch(1);
    // 连接对象
    static ZooKeeper zooKeeper;
    // 用于本地化存储配置信息
    private String url;
    private String username;
    private String password;
    @Override
    public void process(WatchedEvent event) {
        try {
            // 捕获事件状态
            if (event.getType() == Event.EventType.None) {
                if (event.getState() == Event.KeeperState.SyncConnected)
                {
                    System.out.println("连接成功");
                    countDownLatch.countDown();
                } else if (event.getState() ==
                        Event.KeeperState.Disconnected) {
                    System.out.println("连接断开!");
                } else if (event.getState() == Event.KeeperState.Expired)
                {
                    System.out.println("连接超时!");
                    // 超时后服务器端已经将连接释放，需要重新连接服务器端
                    zooKeeper = new ZooKeeper("192.168.60.130:2181",
                            6000,
                            new ZKConnectionWatcher());
                } else if (event.getState() ==
                        Event.KeeperState.AuthFailed) {
                    System.out.println("验证失败!");
                }
                // 当配置信息发生变化时
            } else if (event.getType() == EventType.NodeDataChanged) {
                initValue();
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    // 构造方法
    public MyConfigCenter() {
        initValue();
    }
    // 连接zookeeper服务器，读取配置信息
    public void initValue() {
        try {
            // 创建连接对象
            zooKeeper = new ZooKeeper(IP, 5000, this);
            // 阻塞线程，等待连接的创建成功
            countDownLatch.await();
            // 读取配置信息
            this.url = new String(zooKeeper.getData("/config/url", true,
                    null));
            this.username = new
                    String(zooKeeper.getData("/config/username", true, null));
            this.password = new
                    String(zooKeeper.getData("/config/password", true, null));
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    public static void main(String[] args) {
        try {
            MyConfigCenter myConfigCenter = new MyConfigCenter();
            for (int i = 1; i <= 20; i++) {
                Thread.sleep(5000);
                System.out.println("url:"+myConfigCenter.getUrl());
                System.out.println("username:"+myConfigCenter.getUsername());
                System.out.println("password:"+myConfigCenter.getPassword());
                System.out.println("########################################");
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    public String getUrl() {
        return url;
    }
    public void setUrl(String url) {
        this.url = url;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
}

zookeeper生成分布式唯一ID

在过去的单库单表型系统中，通常可以使用数据库字段自带的auto_increment属性来自动为每条记录生成一个唯一的ID。但是分库分表后，就无法在依靠数据库的auto_increment属性来唯一标识一条记录了。此时我们就可以用zookeeper在分布式环境下生成全局唯一ID。
设计思路：
1.连接zookeeper服务器
2.指定路径生成临时有序节点
3.取序列号及为分布式环境下的唯一ID

代码如下：

package com.ali.zk;

import java.util.concurrent.CountDownLatch;
import com.ali.zk.ZKConnectionWatcher;
import org.apache.zookeeper.CreateMode;
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;
public class GloballyUniqueId implements Watcher {
    // zk的连接串
    String IP = "192.168.60.130:2181";
    // 计数器对象
    CountDownLatch countDownLatch = new CountDownLatch(1);
    // 用户生成序号的节点
    String defaultPath = "/uniqueId";
    // 连接对象
    ZooKeeper zooKeeper;
    @Override
    public void process(WatchedEvent event) {
        try {
            // 捕获事件状态
            if (event.getType() == Watcher.Event.EventType.None) {
                if (event.getState() ==
                        Watcher.Event.KeeperState.SyncConnected) {
                    System.out.println("连接成功");
                    countDownLatch.countDown();
                } else if (event.getState() ==
                        Watcher.Event.KeeperState.Disconnected) {
                    System.out.println("连接断开!");
                } else if (event.getState() ==
                        Watcher.Event.KeeperState.Expired) {
                    System.out.println("连接超时!");
                    // 超时后服务器端已经将连接释放，需要重新连接服务器端
                    zooKeeper = new ZooKeeper(IP, 6000,
                            new ZKConnectionWatcher());
                } else if (event.getState() ==
                        Watcher.Event.KeeperState.AuthFailed) {
                    System.out.println("验证失败!");
                }
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    // 构造方法
    public GloballyUniqueId() {
        try {
            //打开连接
            zooKeeper = new ZooKeeper(IP, 5000, this);
            // 阻塞线程，等待连接的创建成功
            countDownLatch.await();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    // 生成id的方法
    public String getUniqueId() {
        String path = "";
        try {
            //创建临时有序节点
            path = zooKeeper.create(defaultPath, new byte[0],
                    Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        // /uniqueId0000000001
        return path.substring(9);
    }
    public static void main(String[] args) {
        GloballyUniqueId globallyUniqueId = new GloballyUniqueId();
        for (int i = 1; i <= 5; i++) {
            String id = globallyUniqueId.getUniqueId();
            System.out.println(id);
        }
    }
}

分布式锁

分布式锁有多种实现方式，比如通过数据库、redis都可实现。作为分布式协同工具ZooKeeper，当然也有着标准的实现方式。下面介绍在zookeeper中如何实现排他锁。

设计思路：
1.每个客户端往/Locks下创建临时有序节点/Locks/Lock000000001
2.客户端取得/Locks下子节点，并进行排序，判断排在最前面的是否为自己，如果自己的锁节点在第一位，代表获取锁成功
3.如果自己的锁节点不在第一位，则监听自己前一位的锁节点。例如，自己锁节点Lock_000000002，那么则监听Lock_000000001
4.当前一位锁节点（Lock_000000001）对应的客户端执行完成，释放了锁，将会触发客户端（Lock_000000002）的逻辑
5.监听客户端重新执行第2步逻辑，判断自己是否获得了锁

如下：

package com.ali.zk;

import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
public class MyLock {
    // zk的连接串
    String IP = "192.168.60.130:2181";
    // 计数器对象
    CountDownLatch countDownLatch = new CountDownLatch(1);
    //ZooKeeper配置信息
    ZooKeeper zooKeeper;
    private static final String LOCK_ROOT_PATH = "/Locks";
    private static final String LOCK_NODE_NAME = "Lock_";
    private String lockPath;
    // 打开zookeeper连接
    public MyLock() {
        try {
            zooKeeper = new ZooKeeper(IP, 5000, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getType() == Event.EventType.None) {
                        if (event.getState() ==
                                Event.KeeperState.SyncConnected) {
                            System.out.println("连接成功!");
                            countDownLatch.countDown();
                        }
                    }
                }
            });
            countDownLatch.await();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    //获取锁
    public void acquireLock() throws Exception {
        //创建锁节点
        createLock();
        //尝试获取锁
        attemptLock();
    }
    //创建锁节点
    private void createLock() throws Exception {
        //判断Locks是否存在，不存在创建
        Stat stat = zooKeeper.exists(LOCK_ROOT_PATH, false);
        if (stat == null) {
            zooKeeper.create(LOCK_ROOT_PATH, new byte[0],
                    ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        }
        // 创建临时有序节点
        lockPath = zooKeeper.create(LOCK_ROOT_PATH + "/" +
                        LOCK_NODE_NAME, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,
                CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println("节点创建成功:" + lockPath);
    }
    //监视器对象，监视上一个节点是否被删除
    Watcher watcher = new Watcher() {
        @Override
        public void process(WatchedEvent event) {
            if (event.getType() == Event.EventType.NodeDeleted) {
                synchronized (this) {
                    notifyAll();
                }
            }
        }
    };
    //尝试获取锁
    private void attemptLock() throws Exception {
        // 获取Locks节点下的所有子节点
        List list = zooKeeper.getChildren(LOCK_ROOT_PATH, false);
        // 对子节点进行排序
        Collections.sort(list);
        // /Locks/Lock_000000001
        int index =
                list.indexOf(lockPath.substring(LOCK_ROOT_PATH.length() + 1));
        if (index == 0) {
            System.out.println("获取锁成功!");
            return;
        } else {
            // 上一个节点的路径
            String path = list.get(index - 1);
            Stat stat = zooKeeper.exists(LOCK_ROOT_PATH + "/" + path,
                    watcher);
            if (stat == null) {
                attemptLock();
            } else {
                synchronized (watcher) {
                    watcher.wait();
                }
                attemptLock();
            }
        }
    }
    //释放锁
    public void releaseLock() throws Exception {
        //删除临时有序节点
        zooKeeper.delete(this.lockPath,-1);
        zooKeeper.close();
        System.out.println("锁已经释放:"+this.lockPath);
    }
    public static void main(String[] args) {
        try {
            MyLock myLock = new MyLock();
            myLock.createLock();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

package com.ali.zk;

public class TicketSeller {
    private void sell(){
        System.out.println("售票开始");
        // 线程随机休眠数毫秒，模拟现实中的费时操作
        int sleepMillis = 5000;
        try {
            //代表复杂逻辑执行了一段时间
            Thread.sleep(sleepMillis);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("售票结束");
    }
    public void sellTicketWithLock() throws Exception {
        MyLock lock = new MyLock();
        // 获取锁
        lock.acquireLock();
        sell();
        //释放锁
        lock.releaseLock();
    }
    public static void main(String[] args) throws Exception {
        TicketSeller ticketSeller = new TicketSeller();
        for(int i=0;i<10;i++){
            ticketSeller.sellTicketWithLock();
        }
    }
}