Zookeeper之觀察機制(配置服務)

ConnectionWatcher

// vv ConnectionWatcher
public class ConnectionWatcher implements Watcher {

  private static final int SESSION_TIMEOUT = 5000;

  protected ZooKeeper zk;
  private CountDownLatch connectedSignal = new CountDownLatch(1);

  public void connect(String hosts) throws IOException, InterruptedException {
    zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
    connectedSignal.await();
  }

  @Override
  public void process(WatchedEvent event) {
    if (event.getState() == KeeperState.SyncConnected) {
      connectedSignal.countDown();
    }
  }

  public void close() throws InterruptedException {
    zk.close();
  }
}
// ^^ ConnectionWatcher

ActiveKeyValueStore

//vv ActiveKeyValueStore-Write
  public void write(String path, String value) throws InterruptedException,
      KeeperException {
    Stat stat = zk.exists(path, false);
    if (stat == null) {
      zk.create(path, value.getBytes(CHARSET), Ids.OPEN_ACL_UNSAFE,
          CreateMode.PERSISTENT);
    } else {
      zk.setData(path, value.getBytes(CHARSET), -1);
    }
  }
//^^ ActiveKeyValueStore-Write
//^^ ActiveKeyValueStore
//vv ActiveKeyValueStore-Read
  public String read(String path, Watcher watcher) throws InterruptedException,
      KeeperException {
    byte[] data = zk.getData(path, watcher, null/*stat*/);
    return new String(data, CHARSET);
  }
//^^ ActiveKeyValueStore-Read
//vv ActiveKeyValueStore
}
//^^ ActiveKeyValueStore

ConfigUpdater

// vv ConfigUpdater
public class ConfigUpdater {

  public static final String PATH = "/config";

  private ActiveKeyValueStore store;
  private Random random = new Random();

  public ConfigUpdater(String hosts) throws IOException, InterruptedException {
    store = new ActiveKeyValueStore();
    store.connect(hosts);
  }

  public void run() throws InterruptedException, KeeperException {
    while (true) {
      String value = random.nextInt(100) + "";
      store.write(PATH, value);
      System.out.printf("Set %s to %s\n", PATH, value);
      TimeUnit.SECONDS.sleep(random.nextInt(10));
    }
  }

  public static void main(String[] args) throws Exception {
    ConfigUpdater configUpdater = new ConfigUpdater("192.168.8.88");
    configUpdater.run();
  }
}
// ^^ ConfigUpdater

ConfigWatcher

// vv ConfigWatcher
public class ConfigWatcher implements Watcher {

  private ActiveKeyValueStore store;

  public ConfigWatcher(String hosts) throws IOException, InterruptedException {
    store = new ActiveKeyValueStore();
    store.connect(hosts);
  }

  public void displayConfig() throws InterruptedException, KeeperException {
    String value = store.read(ConfigUpdater.PATH, this);
    System.out.printf("Read %s as %s\n", ConfigUpdater.PATH, value);
  }

  @Override
  public void process(WatchedEvent event) {
    if (event.getType() == EventType.NodeDataChanged) {
      try {
        displayConfig();
      } catch (InterruptedException e) {
        System.err.println("Interrupted. Exiting.");        
        Thread.currentThread().interrupt();
      } catch (KeeperException e) {
        System.err.printf("KeeperException: %s. Exiting.\n", e);        
      }
    }
  }

  public static void main(String[] args) throws Exception {
    ConfigWatcher configWatcher = new ConfigWatcher("192.168.8.88");
    configWatcher.displayConfig();

    // stay alive until process is killed or thread is interrupted
    Thread.sleep(Long.MAX_VALUE);
  }
}
//^^ ConfigWatcher

可靠的配置服務
ResilientActiveKeyValueStore

public class ResilientActiveKeyValueStore extends ConnectionWatcher {

  private static final Charset CHARSET = Charset.forName("UTF-8");
  private static final int MAX_RETRIES = 5;
  private static final int RETRY_PERIOD_SECONDS = 10;

//vv ResilientActiveKeyValueStore-Write
  public void write(String path, String value) throws InterruptedException,
      KeeperException {
    int retries = 0;
    while (true) {
      try {
        Stat stat = zk.exists(path, false);
        if (stat == null) {
          zk.create(path, value.getBytes(CHARSET), Ids.OPEN_ACL_UNSAFE,
              CreateMode.PERSISTENT);
        } else {
          zk.setData(path, value.getBytes(CHARSET), stat.getVersion());
        }
        return;
      } catch (KeeperException.SessionExpiredException e) {
        throw e;
      } catch (KeeperException e) {
        if (retries++ == MAX_RETRIES) {
          throw e;
        }
        // sleep then retry
        TimeUnit.SECONDS.sleep(RETRY_PERIOD_SECONDS);
      }
    }
  }
//^^ ResilientActiveKeyValueStore-Write
  public String read(String path, Watcher watcher) throws InterruptedException,
      KeeperException {
    byte[] data = zk.getData(path, watcher, null/*stat*/);
    return new String(data, CHARSET);
  }
}

ResilientConfigUpdater

public class ResilientConfigUpdater {

  public static final String PATH = "/config";

  private ResilientActiveKeyValueStore store;
  private Random random = new Random();

  public ResilientConfigUpdater(String hosts) throws IOException,
      InterruptedException {
    store = new ResilientActiveKeyValueStore();
    store.connect(hosts);
  }

  public void run() throws InterruptedException, KeeperException {
    while (true) {
      String value = random.nextInt(100) + "";
      store.write(PATH, value);
      System.out.printf("Set %s to %s\n", PATH, value);
      TimeUnit.SECONDS.sleep(random.nextInt(10));
    }
  }

//vv ResilientConfigUpdater
  public static void main(String[] args) throws Exception {
    /*[*/while (true) {
      try {/*]*/
        ResilientConfigUpdater configUpdater =
          new ResilientConfigUpdater("192.168.8.88");
        configUpdater.run();
      /*[*/} catch (KeeperException.SessionExpiredException e) {
        // start a new session
      } catch (KeeperException e) {
        // already retried, so exit
        e.printStackTrace();
        break;
      }
    }/*]*/
  }
//^^ ResilientConfigUpdater
}