1.6.1 连接Zookeeper

1.6.1.1 添加 Maven 依赖

<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.7.0</version>
</dependency>

1.6.1.2 编写 Java 代码

import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

import java.io.IOException;

public class ConnectZookeeper {
    private static final String ZK_HOST = "192.168.200.138:2181";
    private static final int CONNECT_TIMEOUT = 20000;  // 设置超时时间需要合理

    public static void main(String[] args) throws IOException, InterruptedException {
        // 创建一个ZooKeeper客户端实例
        ZooKeeper zk = new ZooKeeper(ZK_HOST, CONNECT_TIMEOUT, event -> {
            System.out.println("Watcher的process被调用了");
            if (event.getState() == Watcher.Event.KeeperState.SyncConnected) {
                System.out.println("连接成功");
            }
            if (event.getState() == Watcher.Event.KeeperState.Closed) {
                System.out.println("连接关闭");
            }
        });

        System.out.println("客户端开始连接ZK服务器");

        // 等待连接到ZooKeeper
        ZooKeeper.States state = zk.getState();
        System.out.println(state);
        Thread.sleep(20000);

        state = zk.getState();
        System.out.println(state);

        Thread.sleep(20000);
        zk.close();
    }
}

可以看到如下运行结果：

客户端开始连接ZK服务器
CONNECTING
Watcher的process被调用了
连接成功
CONNECTED
Watcher的process被调用了
连接关闭

1.6.2 增删改查操作及Watcher监听

import org.apache.zookeeper.*;

import java.io.IOException;

public class ZookeeperCRUD {
    private static final String ZK_HOST = "192.168.200.138:2181";
    private static final int CONNECT_TIMEOUT = 20000;  // 设置超时时间需要合理
    private static final String PATH = "/my_crud_node";

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        // 创建一个ZooKeeper客户端实例
        ZooKeeper zk = new ZooKeeper(ZK_HOST, CONNECT_TIMEOUT, event -> {
            if (event.getState() == Watcher.Event.KeeperState.SyncConnected) {
                System.out.println("连接成功");
            }
            // 监听数据变化
            if (event.getType()== Watcher.Event.EventType.NodeDataChanged) {
                System.out.println("数据被改变");
            }
            if (event.getType()== Watcher.Event.EventType.NodeDeleted) {
            	System.out.println("节点已删除");
            }
            if (event.getState() == Watcher.Event.KeeperState.Closed) {
                System.out.println("连接关闭");
            }
        });

        ZooKeeper.States state = zk.getState();
        System.out.println(state);
        Thread.sleep(20000);

        state = zk.getState();
        System.out.println(state);
        Thread.sleep(2000);

        //对节点进行增删改查
        // PERSISTENT 节点是一种持久化的节点类型，它在客户端会话结束时不会自动删除，而是会一直保留在 ZooKeeper 中，直到被显式删除
        zk.create(PATH, "I like ZooKeeper".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        byte[] data;
        data = zk.getData(PATH, true, null);
        System.out.println(new String(data));

        zk.setData(PATH, "I like Java".getBytes(), -1);
        // 第二个参数设置成true，表示开启监听
        data = zk.getData(PATH, true, null);
        System.out.println(new String(data));

        zk.delete(PATH, -1);

        zk.close();
    }
}