zookeeper应用场景
配置中心：
将配置信息存在zk中的一个节点中，同时给该节点注册一个数据节点变更的watcher监听，一旦节数据发生变更，所有的订阅该节点的客户端都可以获取数据变更通知。
案例：
public class ZKConnectionWatcher implements Watcher { // 计数器对象 static CountDownLatch countDownLatch = new CountDownLatch(1); // 连接对象 static ZooKeeper zooKeeper; @Override public void process(WatchedEvent event) { try { // 事件类型 if (event.getType() == Event.EventType.None) { if (event.getState() == Event.KeeperState.SyncConnected) { System.out.println("连接创建成功"); countDownLatch.countDown(); // 通知线程可以继续往下执行了 } else if (event.getState() == Event.KeeperState.Disconnected) { System.out.println("断开连接"); } else if (event.getState() == Event.KeeperState.Expired) { System.out.println("会话超时"); // 会话超时，重新创建 zooKeeper = new ZooKeeper("192.168.43.182:2181", 5000, new ZKConnectionWatcher()); } else if (event.getState() == Event.KeeperState.AuthFailed) { System.out.println("认证失败"); } } } catch (Exception e) { e.printStackTrace(); } } public static void main(String[] args) { try { zooKeeper = new ZooKeeper("192.168.43.182:2181", 5000, new ZKConnectionWatcher()); countDownLatch.await(); // 阻塞线程，等待连接的创建 // 会话id System.out.println(zooKeeper.getSessionId()); // 添加授权用户 zooKeeper.addAuthInfo("digest", "fan:123456".getBytes()); byte[] bytes = zooKeeper.getData("/node1", false, null); System.out.println(new String(bytes)); Thread.sleep(5000); System.out.println("结束"); } catch (Exception e) { e.printStackTrace(); } finally { if (zooKeeper != null) { try { zooKeeper.close(); } catch (InterruptedException e) { e.printStackTrace(); } } } } }
分布式唯一ID：
public class GloballyUniqueId implements Watcher { String IP = "192.168.0.105:2181"; // 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 static ZooKeeper zooKeeper; public GloballyUniqueId() { 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(); } catch (Exception e) { e.printStackTrace(); } } @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("连接创建成功"); countDownLatch.countDown(); // 通知线程可以继续往下执行了 } else if (event.getState() == Event.KeeperState.Disconnected) { System.out.println("断开连接"); } else if (event.getState() == Event.KeeperState.Expired) { System.out.println("会话超时"); // 会话超时，重新创建 zooKeeper = new ZooKeeper(IP, 5000, new GloballyUniqueId()); } else if (event.getState() == Event.KeeperState.AuthFailed) { System.out.println("认证失败"); } } } catch (Exception e) { e.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], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL); return path.substring(9); } catch (Exception e) { e.printStackTrace(); } return path; } public static void main(String[] args) { GloballyUniqueId globallyUniqueId = new GloballyUniqueId(); for (int i = 0; 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，有着标准的实现方式。
public class MyLock { String IP = "192.168.0.105:2181"; // 计数器对象 CountDownLatch countDownLatch = new CountDownLatch(1); // 连接对象 static ZooKeeper zooKeeper; private static final String LOCK_ROOT_PATH = "/locks"; private static final String LOCK_NODE_NAME = "/Lock_"; private String lockPath; public MyLock() { try { // 创建连接对象 zooKeeper = new ZooKeeper(IP, 5000, new Watcher() { @Override public void process(WatchedEvent event) { // 捕获事件状态 if (event.getType() == Event.EventType.None) { if (event.getState() == Event.KeeperState.SyncConnected) { System.out.println("连接创建成功"); countDownLatch.countDown(); // 通知线程可以继续往下执行了 } } } }); // 阻塞线程，等待连接的创建成功 countDownLatch.await(); } catch (Exception e) { e.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 { 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 { List<String> list = zooKeeper.getChildren(LOCK_ROOT_PATH, false); // 对子节点进行排序 Collections.sort(list); // /locks/Lock_0000000001 --> Lock_0000000001 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 { 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 e) { e.printStackTrace(); } } }
public class TicketSeller { private void sell() { System.out.println("售票开始"); int sleepMillis = 5000; try { // 代表复杂逻辑执行了一段时间 Thread.sleep(sleepMillis); } catch (Exception 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(); } } }
