Before adding the connected Semaphore semaphore:

My own analysis of the feeling is as follows:

The following code:

package com.qianliu.bigdata.zookeeper;

import org.apache.zookeeper.*;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.util.List;
import java.util.concurrent.CountDownLatch;

public class sampleZkClient {
    private static final String connectString = "192.168.48.132:2181,192.168.48.134:2181,192.168.48.135:2181";
    private static final int sessionTimeout = 2000;

    /** A semaphore, blocking program execution, used to wait for the zookeeper connection to succeed and send a successful signal. */
    /*Once unlocked, because it takes 10 seconds to connect to zookeeper and 5 seconds to execute the program, the program runs to write data to the zookeeper node.
    ，zookeeper There is no connection yet, so the program will report an error.
    */
    static final CountDownLatch connectedSemaphore = new CountDownLatch(1);
    ZooKeeper zkClient = null;

    @Before
    public void testInit() throws Exception{
        zkClient = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                // Get the state of the event
                Event.KeeperState keeperState = event.getState();
                Event.EventType eventType = event.getType();
                // If a connection is established
                if (Event.KeeperState.SyncConnected == keeperState) {
                    if (Event.EventType.None == eventType) {
                        // If the connection is successful, the semaphore is sent to allow subsequent blockers to execute downward.
                        System.out.println("zk Establish connection");
                        connectedSemaphore.countDown();
                    }
                }
            }
        });

        // Blocking
        connectedSemaphore.await();
        System.out.println("..");
    }
    /**
     * Addition, deletion and modification of data
     *
     * @throws InterruptedException
     * @throws KeeperException
     */

    // Create data nodes into zk
    @Test
    public void testCreate() throws KeeperException, InterruptedException {
        // PARAMETER 1: PATH PARAMETER 2: NODE LARGE DATA PARAMETER 3: NODE'S PRIvilege PARAMETER 4: NODE TYPE
        String nodeCreated = zkClient.create("/eclipse4", "hellozk4".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        //Uploaded data can be of any type, but must be converted to byte []
        System.err.println(nodeCreated);

    }

    // Get child nodes
    @Test
    public void getChildren() throws Exception {
        List<String> children = zkClient.getChildren("/", true);
        for (String child : children) {
            System.out.println(child);
        }
        Thread.sleep(Long.MAX_VALUE);
        zkClient.close();
    }

    @After
    public void closeZkConnection() throws Exception{
        zkClient.close();
    }
}

Attach github source code: https://github.com/LUK-qianliu/zookeeperConnection