zookeeper【封神录】下篇

1.客户端API

1.1导入依赖

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.14.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.5.7</version>
        </dependency>
    </dependencies>

1.2代码实现

public class zkClient {
    //一定不要有空格
    private String connectString = "192.168.20.129:2181,192.168.20.130:2181,192.168.20.131:2181";
    private int sessionTimeOut = 2000;
    private ZooKeeper zkClient;

    /**
     * 初始话zookeeper
     * 参数1：连接地址
     * 参数2：超时时间
     * 参数3：监听器
     */
    @Before
    public void init() throws IOException {
        zkClient = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                List<String> children = null;
                try {
                    children = zkClient.getChildren("/", true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                System.out.println("========================");
                for (String child : children) {
                    System.out.println(child);
                }
                System.out.println("========================");
            }
        });
    }

    /**
     * 创建子节点
     * 参数1：创建节点的路径
     * 参数2：节点的数据（转化为字节）
     * 参数3：节点的权限
     * 参数4：节点的类型（临时/永久）
     **/
    @Test
    public void create() throws InterruptedException, KeeperException {
        String nodeCreate = zkClient.create("/class", "s1".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
    }

    /**
     * 监控子节点变化
     * 参数1：要监控的节点目录
     * 参数2：监听器（true:使用初始化是的监听器）
     */
    @Test
    public void getChildren() throws InterruptedException, KeeperException {
        List<String> children = zkClient.getChildren("/", true);
        for (String child : children) {
            System.out.println(child);
        }
        //延时
        Thread.sleep(Long.MAX_VALUE);
    }

    /**
     * 判断节点是否存在
     * 参数1：判断的节点路径
     * 参数：是否使用监听器
     */
    @Test
    public void isExist() throws InterruptedException, KeeperException {
        Stat stat = zkClient.exists("/class", false);
        System.out.println(stat == null ? "不存在" : "存在");
    }
}

1.3写数据原理

1.写入请求直接发送给Leader

• 1.客户端发请求给Leader
• 2.leader执行请求并应答，然后把请求分发给下一个follower
• 3.follower会执行请求并应答。
• 4.当应答数超过半数，Leader就会回复客户端，完成了写请求
• 5.leader会继续发送写请求给剩下的follower

2.写入请求发送给Follower

• 1.客户端发请求给follower，follower没有写权限，立即把写请求发给leader
• 2.leader执行写请求并应答，然后把写请求分发给follower
• 3.follower会执行请求并应答。
• 4.当应答数超过半数，Leader回复follower，由follower回复客户端，完成了写请求
• 5.leader会继续发送写请求给剩下的follower

2.服务器动态上下线

2.1客户端

• 1.获取zookeeper连接
• 2.监听节点的变化
• 3.业务逻辑（睡眠）

public class DisClient {
    private String connectString = "192.168.20.129:2181,192.168.20.130:2181,192.168.20.131:2181";
    private int sessionTimeOut = 2000;
    private ZooKeeper zooKeeper;

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        DisClient client = new DisClient();
        //1.获取zk连接
        client.getConnect();
        //2.监听/servers下面的节点变化
        client.getServerList();
        //3.业务逻辑
        client.business();

    }

    private void business() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE);
    }

    /**
     * 监听服务端（获取节点信息）
     * @throws InterruptedException
     * @throws KeeperException
     */
    private void getServerList() throws InterruptedException, KeeperException {
        List<String> children = zooKeeper.getChildren("/servers", true);
        //服务器地址存放到集合中
        ArrayList<String> list = new ArrayList<>();
        for (String child : children) {
            byte[] data = zooKeeper.getData("/servers/" + child, false, null);
            list.add(new String(data));
        }
        System.out.println(list);

    }

    /**
     * 初始话zookeeper
     * @throws IOException
     */
    private void getConnect() throws IOException {
        zooKeeper = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

                try {
                    getServerList();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } catch (KeeperException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

2.2服务端

• 1.获取zookeeper连接
• 2.创建节点（服务端注册到zookeeper）
• 3.业务逻辑（睡眠）

/**
 * 服务端注册zookeeper
 */
public class DisServer {
    private String connectString = "192.168.20.129:2181,192.168.20.130:2181,192.168.20.131:2181";
    private int sessionTimeOut = 2000;
    private ZooKeeper zooKeeper;

    public static void main(String[] args) throws Exception {
        DisServer dIsServer = new DisServer();
        //1.获取zk连接
        dIsServer.getConnect();
        //2.注册服务器到zk节点（创建节点）
        dIsServer.register(args[0]);
        //3.启动业务逻辑
        dIsServer.business();
    }

    private void business() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE);
    }

    /**
     * 注册服务器（创建节点）
     * @param hostname
     * @throws InterruptedException
     * @throws KeeperException
     */
    private void register(String hostname) throws InterruptedException, KeeperException {
        String create = zooKeeper.create("/servers/"+hostname, hostname.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println(hostname + "已经上线");
    }

    /**
     * 初始化zookeeper
     * @throws IOException
     */
    private void getConnect() throws IOException {
        zooKeeper = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

            }
        });
    }
}

3.分布式锁

Zookeeper的分布式锁实现基于其znode（zk节点）功能。每个znode都可以有数据和子节点，并且每个znode都有一个版本号。Zookeeper的分布式锁利用了znode的版本号特性，同时使用watcher机制实现分布式锁的互斥

3.1执行流程

1. 当一个客户端需要获取锁时，它会在Zookeeper上创建一个临时且有序的znode节点。
2. 客户端通过获取Zookeeper上的znode列表，并判断自己创建的节点是否是所有节点中最小的那个，如果是，则表示客户端获得了锁。
3. 如果客户端没有获得锁，则监听它前面（比它序号小的）的节点，等待锁的释放。
4. 当客户端释放锁时，它会删除自己创建的znode节点，此时，Zookeeper会通知正在等待前面的节点上的watcher机制，让等待锁的客户端尝试重新获取锁

3.2代码实现

/**
 * 分布式锁
 */
public class ZkLock {
    private final String connectString = "192.168.20.129:2181,192.168.20.130:2181,192.168.20.131:2181";
    private final int sessionTimeOut = 2000;
    private final ZooKeeper zooKeeper;
    private String path;

    private CountDownLatch countDownLatch = new CountDownLatch(1);
    private CountDownLatch countPathLatch = new CountDownLatch(1);
    private String currentNode;

    //构造器初始化
    public ZkLock() throws IOException, InterruptedException, KeeperException {
        //1.获取链接
        zooKeeper = new ZooKeeper(connectString, sessionTimeOut, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                //countDownLatch 连接上zookeeper，释放
                if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
                    countDownLatch.countDown();
                }
                //countPathLatch 释放
                if (watchedEvent.getType() == Event.EventType.NodeDeleted && watchedEvent.getPath().equals(path)) {
                    countPathLatch.countDown();

                }
            }
        });
        //等待zookeeper正常连接后，往下执行程序
        countDownLatch.await();

        //2.判断根节点locks是否存在
        Stat stat = zooKeeper.exists("/locks", false);
        if (stat == null) {
            //说明不存在，创建根节点
            zooKeeper.create("/locks", "locks".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        }

    }

    //3.加锁
    public void zkLock() {
        //创建对应的临时带序号的节点
        try {
            currentNode = zooKeeper.create("/locks/" + "seq-", null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

            //判断创建的节点是否是最小的序号节点，如果是，获取到锁，如果不是，监听他前一个结点
            List<String> children = zooKeeper.getChildren("/locks", false);

            //如果只有一个值，直接获取锁，如果不是，则判断
            if (children.size() == 1) {
                //直接枷锁
                return;
            } else {
                //对节点进行排序
                Collections.sort(children);
                //获取节点名称
                String thisNode = currentNode.substring("/locks/".length());
                //通过界节点名称，获取在集合中的下标
                int index = children.indexOf(thisNode);

                //判断下标
                if (index == -1) {
                    System.out.println("数据异常");
                } else if (index == 0) {//第一个数据
                    //直接枷锁
                    return;
                } else {//说明多个节点，进行监听前一个节点
                    path = "/locks/" + children.get(index - 1);
                    zooKeeper.getData(path, true, new Stat());
                    //等待监听
                    countPathLatch.await();
                    return;
                }
            }
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    //4.解锁
    public void unZkLock() {
        //删除节点
        try {
            zooKeeper.delete(currentNode, -1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (KeeperException e) {
            e.printStackTrace();
        }
    }
}

3.3线程测试

public class ZkLockTest {
    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        ZkLock zkLock1 = new ZkLock();
        ZkLock zkLock2 = new ZkLock();
        ZkLock zkLock3 = new ZkLock();

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    zkLock1.zkLock();
                    System.out.println("线程1，获取到锁");
                    Thread.sleep(3 * 1000);
                    zkLock1.unZkLock();
                    System.out.println("线程1，释放锁");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    zkLock2.zkLock();
                    System.out.println("线程2，获取到锁");
                    Thread.sleep(3 * 1000);
                    zkLock2.unZkLock();
                    System.out.println("线程2，释放锁");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    zkLock3.zkLock();
                    System.out.println("线程3，获取到锁");
                    Thread.sleep(3 * 1000);
                    zkLock3.unZkLock();
                    System.out.println("线程3，释放锁");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}

4.Curator框架

Curator是Apache ZooKeeper的一个高级客户端库，旨在使开发人员更容易编写可靠的分布式系统。它为ZooKeeper提供了许多有用的功能，包括连接管理，分布式锁和选举，缓存和观察。Curator还提供了一组易于使用的API，可以轻松管理ZooKeeper的节点和数据。

4.1添加依赖

        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-framework</artifactId>
            <version>5.5.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-client</artifactId>
            <version>5.5.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>5.5.0</version>
        </dependency>

4.2代码实现

    /**
     * 客户端连接
     * @return
     */
    private static CuratorFramework getCuratorFramework() {

        //创建zookeeper的客户端:重试策略，初始化每次重试之间需要等待的时间，基准等待时间为3秒
        ExponentialBackoffRetry policy = new ExponentialBackoffRetry(3000, 3);

        CuratorFramework client = CuratorFrameworkFactory.builder().connectString("192.168.20.129:2181,192.168.20.131:2181,192.168.20.130:2181")
                .connectionTimeoutMs(2000)
                .sessionTimeoutMs(2000)
                .retryPolicy(policy).build();
        client.start();
        System.out.println("zookeeper启动~");
        return client;
    }

4.3创建线程测试

InterProcessMutex lock1 = new InterProcessMutex(getCuratorFramework(), "/locks");
        InterProcessMutex lock2 = new InterProcessMutex(getCuratorFramework(), "/locks");
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    lock1.acquire();
                    System.out.println("线程一获取到锁");
                    Thread.sleep(3000);
                    lock1.release();
                    System.out.println("线程一释放锁");
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    lock2.acquire();
                    System.out.println("线程二获取到锁");
                    Thread.sleep(3000);
                    lock2.release();
                    System.out.println("线程二释放锁");
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }