|NO.Z.00006|——————————|BigDataEnd|——|Hadoop&Zookeeper.V06|——|Zookeeper.v06|开源客户端监听器|获取节点数据.v02|

一、监听节点变化

### --- 监听节点变化

package com.yanqi.zk.demo;

import org.I0Itec.zkclient.IZkChildListener;
import org.I0Itec.zkclient.ZkClient;
import org.apache.zookeeper.client.ZooKeeperSaslClient;

import java.util.List;

/*
演示zkClient如何使用监听器
 */
public class Get_Child_Change {
    public static void main(String[] args) throws InterruptedException {
        //获取到zkClient
        final ZkClient zkClient = new ZkClient("linux121:2181");

        //zkClient对指定目录进行监听(不存在目录:/yanqi-client)，指定收到通知之后的逻辑

        //对/lag-client注册了监听器，监听器是一直监听
        zkClient.subscribeChildChanges("/yanqi-client", new IZkChildListener() {
            //该方法是接收到通知之后的执行逻辑定义
            public void handleChildChange(String path, List<String> childs) throws Exception {
                //打印节点信息
                System.out.println(path + " childs changes ,current childs " + childs);
            }
        });

        //使用zkClient创建节点，删除节点，验证监听器是否运行
        zkClient.createPersistent("/yanqi-client");
        Thread.sleep(1000); //只是为了方便观察结果数据
        zkClient.createPersistent("/yanqi-client/c1");
        Thread.sleep(1000);
        zkClient.delete("/yanqi-client/c1");
        Thread.sleep(1000);

        zkClient.delete("/yanqi-client");

        Thread.sleep(Integer.MAX_VALUE);

        /*
        1 监听器可以对不存在的目录进行监听
        2 监听目录下子节点发生改变，可以接收到通知，携带数据有子节点列表
        3 监听目录创建和删除本身也会被监听到
         */
    }
}

### --- 编译打印

D:\JAVA\jdk1.8.0_231\bin\java.exe "-javaagent:D:\IntelliJIDEA\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=60378:D:\IntelliJIDEA\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath D:\JAVA\jdk1.8.0_231\jre\lib\charsets.jar;D:\JAVA\jdk1.8.0_231\jre\lib\deploy.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\access-bridge-64.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\cldrdata.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\dnsns.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\jaccess.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\jfxrt.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\localedata.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\nashorn.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunec.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunjce_provider.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunmscapi.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunpkcs11.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\zipfs.jar;D:\JAVA\jdk1.8.0_231\jre\lib\javaws.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jce.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jfr.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jfxswt.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jsse.jar;D:\JAVA\jdk1.8.0_231\jre\lib\management-agent.jar;D:\JAVA\jdk1.8.0_231\jre\lib\plugin.jar;D:\JAVA\jdk1.8.0_231\jre\lib\resources.jar;D:\JAVA\jdk1.8.0_231\jre\lib\rt.jar;E:\NO.Z.10000——javaproject\NO.Z.00002.Hadoop\zkclient_demo\target\classes;C:\Users\Administrator\.m2\repository\org\apache\zookeeper\zookeeper\3.4.14\zookeeper-3.4.14.jar;C:\Users\Administrator\.m2\repository\org\slf4j\slf4j-api\1.7.25\slf4j-api-1.7.25.jar;C:\Users\Administrator\.m2\repository\org\slf4j\slf4j-log4j12\1.7.25\slf4j-log4j12-1.7.25.jar;C:\Users\Administrator\.m2\repository\com\github\spotbugs\spotbugs-annotations\3.1.9\spotbugs-annotations-3.1.9.jar;C:\Users\Administrator\.m2\repository\com\google\code\findbugs\jsr305\3.0.2\jsr305-3.0.2.jar;C:\Users\Administrator\.m2\repository\log4j\log4j\1.2.17\log4j-1.2.17.jar;C:\Users\Administrator\.m2\repository\jline\jline\0.9.94\jline-0.9.94.jar;C:\Users\Administrator\.m2\repository\org\apache\yetus\audience-annotations\0.5.0\audience-annotations-0.5.0.jar;C:\Users\Administrator\.m2\repository\io\netty\netty\3.10.6.Final\netty-3.10.6.Final.jar;C:\Users\Administrator\.m2\repository\com\101tec\zkclient\0.2\zkclient-0.2.jar com.yanqi.zk.demo.Get_Child_Change
/yanqi-client childs changes ,current childs []
/yanqi-client childs changes ,current childs [c1]
/yanqi-client childs changes ,current childs []
/yanqi-client childs changes ,current childs null

### --- 结果表明：

~~~     客户端可以对一个不存在的节点进行子节点变更的监听。
~~~     一旦客户端对一个节点注册了子节点列表变更监听之后，那么当该节点的子节点列表发生变更时，
~~~     服务端都会通知客户端，并将最新的子节点列表发送给客户端
~~~     该节点本身的创建或删除也会通知到客户端。

二、获取数据（节点是否存在、更新、删除）

### --- 获取数据（节点是否存在、更新、删除）

package com.yanqi.zk.demo;

import org.I0Itec.zkclient.IZkDataListener;
import org.I0Itec.zkclient.ZkClient;

//使用监听器监听节点数据的变化
public class Get_Data_Change {

    public static void main(String[] args) throws InterruptedException {
        // 获取zkClient对象
        final ZkClient zkClient = new ZkClient("linux121:2181");
        //设置自定义的序列化类型,否则会报错！！
        zkClient.setZkSerializer(new ZkStrSerializer());


        //判断节点是否存在，不存在创建节点并赋值
        final boolean exists = zkClient.exists("/yanqi-client1");
        if (!exists) {
            zkClient.createEphemeral("/yanqi-client1", "123");
        }

        //注册监听器，节点数据改变的类型，接收通知后的处理逻辑定义
        zkClient.subscribeDataChanges("/yanqi-client1", new IZkDataListener() {
            public void handleDataChange(String path, Object data) throws Exception {
                //定义接收通知之后的处理逻辑
                System.out.println(path + " data is changed ,new data " + data);
            }

            //数据删除--》节点删除
            public void handleDataDeleted(String path) throws Exception {
                System.out.println(path + " is deleted!!");
            }
        });

        //更新节点的数据，删除节点，验证监听器是否正常运行
        final Object o = zkClient.readData("/yanqi-client1");
        System.out.println(o);

        zkClient.writeData("/yanqi-client1", "new data");
        Thread.sleep(1000);

        //删除节点
        zkClient.delete("/yanqi-client1");
        Thread.sleep(Integer.MAX_VALUE);
    }
}

package com.yanqi.zk.demo;

import org.I0Itec.zkclient.exception.ZkMarshallingError;
import org.I0Itec.zkclient.serialize.ZkSerializer;

public class ZkStrSerializer implements ZkSerializer {

    //序列化，数据--》byte[]
    public byte[] serialize(Object o) throws ZkMarshallingError {
        return String.valueOf(o).getBytes();
    }

    //反序列化，byte[]--->数据
    public Object deserialize(byte[] bytes) throws ZkMarshallingError {
        return new String(bytes);
    }
}

### --- 运行结果：结果表明可以成功监听节点数据变化或删除事件。

123
/yanqi-client1 data is changed ,new data new data
/yanqi-client1 is deleted!!

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Walter Savage Landor:strove with none,for none was worth my strife.Nature I loved and, next to Nature, Art:I warm'd both hands before the fire of life.It sinks, and I am ready to depart

                                                                                                                                                   ——W.S.Landor

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