本篇文章要讲一下基于 ZooKeeper 的配置中心。简单来说就是发布者对 ZooKeeper 的一个/多个节点进行修改时，通知订阅者进行数据订阅，从而实现动态获取新数据的目的，实现配置的集中式管理和动态更新。

    基于 ZooKeeper 的配置中心实现思路：
    当应用启动时，从 ZooKeeper 的某节点上拉取配置数据，并对该节点注册一个 Watch 监听；但凡 ZooKeeper 上的保存配置数据的节点发生了变化，应用就能收到通知并重新拉取新的配置文件。
    点击查看【processon】
    这部分代码比较简单，如下所示：

    1. public class ZookeeperConfigApp {
    2.     public static final String HOST = "192.168.136.128";
    3.     public static final String PORT = "2181";
    4.     public static MyConfig myConfig = new MyConfig();
    5.     private static ZooKeeper zooKeeper;
    7.     public static void main(String[] args) {
    8.         try {
    9.             // 因为Zookeeper的连接是异步的，需要加上同步工具
    10.             final CountDownLatch countDownLatch = new CountDownLatch(1);
    11.             zooKeeper = new ZooKeeper(HOST + ":" + PORT, 5000, new Watcher() {
    12.                 @Override
    13.                 public void process(WatchedEvent watchedEvent) {
    14.                     if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
    15.                         System.out.println("连接成功");
    16.                         countDownLatch.countDown();
    17.                     }
    18.                     if (watchedEvent.getType() == Event.EventType.NodeDataChanged) {
    19.                         try {
    20.                             if ("/userInfo/username".equals(watchedEvent.getPath())) {
    21.                                 updateUsername(zooKeeper);
    22.                             } else if ("/userInfo/password".equals(watchedEvent.getPath() )) {
    23.                                 updatePassword(zooKeeper);
    24.                             } else if ("/userInfo/url".equals(watchedEvent.getPath())) {
    25.                                 updateUrl(zooKeeper);
    26.                             }
    27.                         } catch (KeeperException e) {
    28.                             e.printStackTrace();
    29.                         } catch (InterruptedException e) {
    30.                             e.printStackTrace();
    31.                         }
    33.                     }
    34.                 }
    35.             });
    37.             countDownLatch.await();
    39.             updateUsername(zooKeeper);
    40.             updatePassword(zooKeeper);
    41.             updateUrl(zooKeeper);
    43.             System.out.println(zooKeeper.getSessionId());
    44.             System.in.read();
    45.             zooKeeper.close();
    46.         } catch (IOException e) {
    47.             e.printStackTrace();
    48.         } catch (InterruptedException e) {
    49.             e.printStackTrace();
    50.         } catch (KeeperException e) {
    51.             e.printStackTrace();
    52.         }
    54.     }
    56.     public static void updateUsername(ZooKeeper zookeeper) throws KeeperException, InterruptedException {
    57.         byte[] data = zookeeper.getData("/userInfo/username", true, null);
    58.         System.out.println("更新用户名 -> " + myConfig.getUsername() + ":" + new String(data));
    59.         myConfig.setUsername(new String(data));
    60.     }
    62.     public static void updatePassword(ZooKeeper zookeeper) throws KeeperException, InterruptedException {
    63.         byte[] data = zookeeper.getData("/userInfo/password", true, null);
    64.         System.out.println("更新密码 -> " + myConfig.getPassword() + ":" + new String(data));
    66.         myConfig.setPassword(new String(data));
    67.     }
    69.     public static void updateUrl(ZooKeeper zookeeper) throws KeeperException, InterruptedException {
    70.         byte[] data = zookeeper.getData("/userInfo/url", true, null);
    71.         System.out.println("更新URL -> " + myConfig.getUrl() + ":" + new String(data));
    73.         myConfig.setUrl(new String(data));
    74.     }
    75. }