ZooKeeper之ZkClient使用示例

在我们实际的生产环境中，zookpeeper是一个很关键的组件，因为zk是用来注册发现服务的服务，zk集群的稳定性与可靠性直接决定了其他服务的稳定。
ZkClient是一个开源的ZooKeeper客户端，是在原生的ZooKeeper API接口之上进行包装，是一个更易使用的ZooKeeper客户端。ZkClient在内部实现了Session超时重连、Watcher反复注册等功能，使得ZooKeeper客户端的繁琐细节对开发人员透明。
实际项目中，我们就使用ZkClient来对zk进行相关操作。为了方便测试，特意在本地开启了一个zk的server并使用zkclient来进行操作。

1.安装Zookeeper并启动服务

首先从网上下载到zookeeper的压缩包，然后解压。
cd到解压的目录以后，bin目录里有zkServer.sh，然后执行./zkServer.sh start，zk服务就已经在本机启动。

如果出现如下页面，则表明此时zk服务已正常启动。

2.用ZkClient监控子节点的变化情况

b按惯例，直接上代码。

    public static void subchild() throws InterruptedException {
        ZkClient zkClient = new ZkClient("localhost:2181", 5000);

        String path = "/mipush";

        zkClient.subscribeChildChanges(path, new IZkChildListener() {
            @Override
            public void handleChildChange(String parentPath, List<String> currentChilds) throws Exception {
                System.out.println(parentPath + "'s child changed, currentChilds: " +　currentChilds);
            }
        });

        if(zkClient.exists(path)) {
            zkClient.deleteRecursive(path);
            // zkClient.delete(path);
            System.out.println("delete " + path + " successful");
        }
        zkClient.createPersistent(path);
        Thread.sleep(1000);
        System.out.println("now child path is: " + zkClient.getChildren(path));
        zkClient.createPersistent(path + "/p1");
        Thread.sleep(1000);
        System.out.println("now child path is: " + zkClient.getChildren(path));
        zkClient.createPersistent(path + "/p2", "abc");
        Thread.sleep(1000);
        System.out.println("now child path is: " + zkClient.getChildren(path));
    }

将上部分代码成功运行起来以后，结果如下：

Node /mipush deleted.
Node /mipush changed, new data: null
/mipush's child changed, currentChilds: []
now child path is: []
/mipush's child changed, currentChilds: [p1]
now child path is: [p1]
/mipush's child changed, currentChilds: [p1, p2]
now child path is: [p1, p2]

3.用ZkClient监控节点数据变化情况

    public static void changedata() throws InterruptedException {
        ZkClient zkClient = new ZkClient("localhost:2181", 5000);
        String path = "/mipush";
        if(zkClient.exists(path)) {
            zkClient.deleteRecursive(path);
            // zkClient.delete(path);
            System.out.println("delete " + path + " successful");
        }
        zkClient.createPersistent(path, "abc");

        zkClient.subscribeDataChanges(path, new IZkDataListener() {
            @Override
            public void handleDataChange(String dataPath, Object data) throws Exception {
                System.out.println("Node " + dataPath + " changed, new data: " + data);
            }

            @Override
            public void handleDataDeleted(String dataPath) throws Exception {
                System.out.println("Node " + dataPath + " deleted.");
            }
        });

        // 读取节点数据
        System.out.println("now data is: " + zkClient.readData(path).toString());
        zkClient.writeData(path, "def");
        Thread.sleep(1000);
        System.out.println("Node exists: " + zkClient.exists(path));
        zkClient.delete(path);
        System.out.println("Node exists: " + zkClient.exists(path));
    }

运行结果如下：

delete /mipush successful
now data is: abc
Node /mipush changed, new data: def
Node exists: true
Node exists: false