Zookeeper API

CreateMode.PERSISTENT); } public static void main(String[] args) { // znode path String path = "/MyFirstZnode"; // Assign path to znode // data in byte array byte[] data = "My first zookeeper app".getBytes(); // Declare data try { conn = new ZooKeeperConnection(); zk = conn.connect("localhost"); create(path, data); // Create the data to the specified path conn.close(); } catch (Exception e) { System.out.println(e.getMessage()); //Catch error message } }}一旦编译和执行应用程序，将在ZooKeeper集合中创建具有指定数据的znode。你可以使用ZooKeeper CLI zkCli.sh 进行检查。cd /path/to/zookeeperbin/zkCli.sh>>> get /MyFirstZnodeExists - 检查Znode的存在ZooKeeper类提供了 exists 方法来检查znode的存在。如果指定的znode存在，则返回一个znode的元数据。exists方法的签名如下： exists(String path, boolean watcher)path- Znode路径 watcher - 布尔值，用于指定是否监视指定的znode让我们创建一个新的Java应用程序来检查ZooKeeper API的“exists”功能。创建文件“ZKExists.java”。在main方法中，使用“ZooKeeperConnection”对象创建ZooKeeper对象“zk”。然后，使用自定义“path”调用“zk”对象的“exists”方法。完整的列表如下： 编码：ZKExists.javaimport java.io.IOException;import org.apache.zookeeper.ZooKeeper;import org.apache.zookeeper.KeeperException;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher;import org.apache.zookeeper.Watcher.Event.KeeperState;import org.apache.zookeeper.data.Stat;public class ZKExists { private static ZooKeeper zk; private static ZooKeeperConnection conn; // Method to check existence of znode and its status, if znode is available. public static Stat znode_exists(String path) throws KeeperException,InterruptedException { return zk.exists(path, true); } public static void main(String[] args) throws InterruptedException,KeeperException { String path = "/MyFirstZnode"; // Assign znode to the specified path try { conn = new ZooKeeperConnection(); zk = conn.connect("localhost"); Stat stat = znode_exists(path); // Stat checks the path of the znode if(stat != null) { System.out.println("Node exists and the node version is " + stat.getVersion()); } else { System.out.println("Node does not exists"); } } catch(Exception e) { System.out.println(e.getMessage()); // Catches error messages } }}一旦编译和执行应用程序，你将获得以下输出。Node exists and the node version is 1.getData方法ZooKeeper类提供 getData 方法来获取附加在指定znode中的数据及其状态。 getData 方法的签名如下： getData(String path, Watcher watcher, Stat stat)path - Znode路径。watcher - 监视器类型的回调函数。当指定的znode的数据改变时，ZooKeeper集合将通过监视器回调进行通知。这是一次性通知。 stat - 返回znode的元数据。让我们创建一个新的Java应用程序来了解ZooKeeper API的 getData 功能。创建文件 ZKGetData.java 。在main方法中，使用 ZooKeeperConnection 对象创建一个ZooKeeper对象 zk 。然后，使用自定义路径调用zk对象的 getData 方法。下面是从指定节点获取数据的完整程序代码： 编码：ZKGetData.javaimport java.io.IOException;import java.util.concurrent.CountDownLatch;import org.apache.zookeeper.ZooKeeper;import org.apache.zookeeper.KeeperException;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher;import org.apache.zookeeper.Watcher.Event.KeeperState;import org.apache.zookeeper.data.Stat;public class ZKGetData { private static ZooKeeper zk; private static ZooKeeperConnection conn; public static Stat znode_exists(String path) throws KeeperException,InterruptedException { return zk.exists(path,true); } public static void main(String[] args) throws InterruptedException, KeeperException { String path = "/MyFirstZnode"; final CountDownLatch connectedSignal = new CountDownLatch(1); try { conn = new ZooKeeperConnection(); zk = conn.connect("localhost"); Stat stat = znode_exists(path); if(stat != null) { byte[] b = zk.getData(path, new Watcher() { public void process(WatchedEvent we) { if (we.getType() == Event.EventType.None) { switch(we.getState()) { case Expired: connectedSignal.countDown(); break; } } else { String path = "/MyFirstZnode"; try { byte[] bn = zk.getData(path, false, null); String data = new String(bn, "UTF-8"); System.out.println(data); connectedSignal.countDown(); } catch(Exception ex) { System.out.println(ex.getMessage()); } } } }, null); String data = new String(b, "UTF-8"); System.out.println(data); co