Java 使用ZkClient操作Zookeeper

一、介绍

　　这里主要记录通过Java调用API来操作Zookeeper集群的数据，对于zookeeper集群的搭建或者命令，可以参考：

　　目前接触到的Java操作Zookeeper，有两套API，一套是zookeeper官方提供的（zookeeper），另外一套是封装了官方API的API（zkClient），从描述上来看，就知道，官方的API可能不是那么好用，不然也不会在封装。　　

二、zookeeper API

2.1、导入依赖

　　使用zookeeper官方api的时候，请保证jar包的版本，和zk集群中zk的版本相同

<!-- https://mvnrepository.com/artifact/org.apache.zookeeper/zookeeper -->

<dependency>

    <groupId>org.apache.zookeeper</groupId>

    <artifactId>zookeeper</artifactId>

    <version>3.4.7</version>

</dependency>

2.2、连接zk集群

　　下面是代码示例，两种形式（分别使用匿名类和Lambda表达式）：

package cn.ganlixin.zk;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.WatchedEvent;

import org.apache.zookeeper.Watcher;

import org.apache.zookeeper.ZooKeeper;

import org.junit.Test;

import java.io.IOException;

public class ZookeeperDemo {

    @Test

    public void connectZkCluster() throws IOException, KeeperException, InterruptedException {

        // 构造方法

        // ZooKeeper(String connectString, int sessionTimeout, Watcher watcher)

        // 匿名对象形式

        ZooKeeper zooKeeper = new ZooKeeper(

                "192.168.1.3:2181,192.168.1.4:2181,192.168.1.5:2181",

                20000,

                new Watcher() {

                    @Override

                    public void process(WatchedEvent watchedEvent) {

                        // 发生变更的节点路径

                        String path = watchedEvent.getPath();

                        System.out.println("path:" + path);

                        // 通知状态

                        Watcher.Event.KeeperState state = watchedEvent.getState();

                        System.out.println("KeeperState:" + state);

                        // 事件类型

                        Watcher.Event.EventType type = watchedEvent.getType();

                        System.out.println("EventType:" + type);

                    }

                }

        );

        // 关闭连接

        zooKeeper.close();

        // Lamdba形式

        ZooKeeper zk = new ZooKeeper(

                "192.168.1.3:2181,192.168.1.4:2181,192.168.1.5:2181",

                20000,

                watchedEvent -> {

                    // 发生变更的节点路径

                    String path = watchedEvent.getPath();

                    System.out.println("path:" + path);

                    // 通知状态

                    Watcher.Event.KeeperState state = watchedEvent.getState();

                    System.out.println("KeeperState:" + state);

                    // 事件类型

                    Watcher.Event.EventType type = watchedEvent.getType();

                    System.out.println("EventType:" + type);

                }

        );

        zk.close();

    }

}

　　运行上面的代码，控制台输出如下（输出了两遍，是因为创建了两次连接）

path:null

KeeperState:SyncConnected

EventType:None

path:null

KeeperState:SyncConnected

EventType:None

2.3、操作数据操作

　　操作Zk中的数据，方式也很简单，只需要使用创建的zk连接，调用对应的方法即可（方法名与zk命令行中命令相同）

package cn.ganlixin.zk;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.KeeperException;

import org.apache.zookeeper.ZooDefs;

import org.apache.zookeeper.ZooKeeper;

import org.apache.zookeeper.data.Stat;

import org.junit.Test;

import java.io.IOException;

public class ZookeeperDemo {

    @Test

    public void manageData() throws KeeperException, InterruptedException, IOException {

        // 创建zk连接

        ZooKeeper zk = new ZooKeeper(

                "192.168.1.3:2181,192.168.1.4:2181,192.168.1.5:2181",

                20000,

                null

        );

        // 创建节点

        zk.create("/abc", "123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        // 获取节点数据

        // getData(String path, boolean watch, Stat stat);

        Stat stat = new Stat();

        byte[] data = zk.getData("/abc", false, stat);

        System.out.println(new String(data));       // 数据内容 123

        System.out.println(stat.getDataLength());   // 节点状态（数据长度） 3

        // 对/abc进行watch

        zk.getData("/abc",

                watchedEvent -> {

                    System.out.println("path:" + watchedEvent.getPath());

                    System.out.println("KeeperState:" + watchedEvent.getState());

                    System.out.println("EventType:" + watchedEvent.getType());

                },

                null);

        // 设置节点数据

        // setData(String path, byte[] data, int version)

        // 指定version为-1，表示不关心版本

        zk.setData("/abc", "456".getBytes(), -1);

        // 设置两次，第二次不会触发通知

        zk.setData("/abc", "789".getBytes(), -1);

        // 阻塞，以等待通知

        Thread.sleep(1000);

        zk.close();

    }

}

　　上面的程序，运行输出结果如下：

123

3

path:/abc

KeeperState:SyncConnected

EventType:NodeDataChanged

　　可以看到，只显示了一次通知，和与预期相符。

三、zkClient API

　　因为Zookeeper API比较复杂，使用并不方便，所以出现了ZkClient，ZkClient对Zookeeper API进行了封装，利用ZkClient可以更加方便地对Zookeeper进行操作。

3.1、导入依赖

　　因为zkClient是对zookeeper的再封装，所以需要注意zkClient中zookeeper的版本与zk集群的版本相同，可以在maven仓库中查看对应关系

<!-- https://mvnrepository.com/artifact/com.101tec/zkclient -->

<dependency>

    <groupId>com.101tec</groupId>

    <artifactId>zkclient</artifactId>

    <version>0.10</version>

</dependency>

3.2、使用示例

　　下面是个简单的示例：

package cn.ganlixin.zk;

import org.I0Itec.zkclient.IZkChildListener;

import org.I0Itec.zkclient.IZkStateListener;

import org.I0Itec.zkclient.ZkClient;

import org.apache.zookeeper.CreateMode;

import org.apache.zookeeper.Watcher;

import org.junit.Test;

import java.util.List;

public class ZkClientDemo {

    @Test

    public void testConn() throws InterruptedException {

        ZkClient zkClient = new ZkClient(

                "192.168.1.3:2181,192.168.1.4:2181,192.168.1.5:2181",

                20000

        );

        // 创建节点

        zkClient.createPersistent("/abc", "hello");

        zkClient.createEphemeral("/xyz", "world");

        zkClient.create("/opq", "world", CreateMode.EPHEMERAL_SEQUENTIAL);

        String data = zkClient.readData("/abc");

        System.out.println(data);

        // 监听状态变化

        zkClient.subscribeStateChanges(new IZkStateListener() {

            @Override

            public void handleStateChanged(Watcher.Event.KeeperState keeperState) throws Exception {

                System.out.println("state:" + keeperState);

            }

            @Override

            public void handleNewSession() throws Exception {

                System.out.println("new session");

            }

            @Override

            public void handleSessionEstablishmentError(Throwable throwable) throws Exception {

                throwable.printStackTrace();

            }

        });

        // 监听子节点发生变化

        zkClient.subscribeChildChanges("/", new IZkChildListener() {

            @Override

            public void handleChildChange(String path, List<String> list) throws Exception {

                System.out.println("watch path:" + path);

                // 输出所有子节点

                list.forEach(str -> {

                    System.out.println(str);

                });

            }

        });

        Thread.sleep(100000);

    }

}

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