15 ZooKeeper 使用异步API获取子节点列表

青旅半醒 2023-01-11 09:29 97阅读 0赞

**代码示例**

package learn.zk.base;
    
    import org.apache.zookeeper.AsyncCallback;
    import org.apache.zookeeper.WatchedEvent;
    import org.apache.zookeeper.Watcher;
    import org.apache.zookeeper.ZooKeeper;
    import org.apache.zookeeper.data.Stat;
    
    import java.util.List;
    import java.util.concurrent.CountDownLatch;
    
    /**
     * @PackageName : learn.zk.base
     * @ClassName : Zk_GetChildren_API_ASync
     * @Author : LingYi
     * @Date : 2021/1/26 20:32
     * @Description : 使用异步API获取子节点列表
     */
    public class Zk_GetChildren_API_ASync implements Watcher {
        /**
         * zookeeper地址
         */
        static final String CONNECT_ADDR = "192.168.31.207:2181,192.168.31.244:2181,192.168.31.212:2181";
        /**
         * session超时时间
         */
        static final int SESSION_OUT_TIME = 4000;//ms
        /**
         * 信号量，阻塞程序执行，用于等待zookeeper连接成功，发送成功信号
         */
        static final CountDownLatch connectedSemaphore = new CountDownLatch(1);
    
        public static void main(String[] args) throws Exception {
            ZooKeeper zk = new ZooKeeper(CONNECT_ADDR, SESSION_OUT_TIME, new Zk_GetChildren_API_ASync());
            connectedSemaphore.await();
            System.out.println("......");
    
            /**
             * path: 路径
             * watch：是否注册watch
             * ZkChildrenASync：回调方法
             * Object：传递一个上下文
             **/
            zk.getChildren("/", true, new ZkChildrenASync(), "Context");
    
            zk.close();
        }
    
        @Override
        public void process(WatchedEvent event) {
            if (Event.KeeperState.SyncConnected == event.getState() && Event.EventType.None == event.getType()) {
                //如果建立连接成功，则发送信号量，让后续阻塞程序向下执行
                connectedSemaphore.countDown();
                System.out.println("zk 建立连接");
            }
        }
    }
    
    
    /**
     * @PackageName : learn.zk.base
     * @ClassName : ZkChildrenASync
     * @Description : 异步回调
     */
    class ZkChildrenASync implements AsyncCallback.Children2Callback {
    
        @Override
        public void processResult(int rc, String path, Object ctx, List<String> children, Stat stat) {
            System.out.println("rc:" + rc + ",path：" + path + "，ctx：" + ctx.toString() + ",children:" + children + ",stat:" + stat);
        }
    }

**执行结果：**

![20210126211125807.png][]

[20210126211125807.png]: /images/20221119/889bcb10361c430f94d6971c173c20de.png