ZooKeeper Java API学习笔记（一）

ZooKeeper 官方提供的API，相比较Curator或者zkclient，比较晦涩，不易使用。不过它是官方API，提供使用ZK的基本操作。下面给出使用API的简单例子（刚开始学习，可能有不对之处，欢迎指出）。

1， pom文件引入依赖

核心依赖是

        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.9</version>
        </dependency>

下面是完整pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.yq</groupId>
    <artifactId>ZKClientDemo</artifactId>
    <version>2.0</version>
    <packaging>jar</packaging>


    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>

        <lombok.version>1.16.14</lombok.version>
        <fastjson.version>1.1.33</fastjson.version>
        <commons.io.version>2.5</commons.io.version>
        <common.lang.version>3.5</common.lang.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.9</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>${lombok.version}</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>${fastjson.version}</version>
        </dependency>

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>${common.lang.version}</version>
        </dependency>
    </dependencies>

    <build>
        <finalName>ZKClientDemo</finalName>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>true</filtering>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

2，主要代码

MyZooKeeper 负责连接到zk上，创建path，获取数据，删除path，以及watch zk上的额变化。
完整的代码在这里，欢迎加星，fork。

package com.yq.service;

import lombok.extern.slf4j.Slf4j;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;

import java.io.IOException;
import java.util.concurrent.CountDownLatch;


@Slf4j
public class MyZooKeeper implements Watcher {
    protected CountDownLatch countDownLatch = new CountDownLatch(1);

    private static final int SESSION_TIME = 2000;
    public static ZooKeeper zooKeeper = null;

    private static final String PATH_NAME = "/yqPath";

    @Override
    public void process(WatchedEvent event) {
        log.info("event notification={}", event.getState() );
        String path = event.getPath();
        log.info("type={}. path={}", event.getType(), path);
        if(event.getState()==KeeperState.SyncConnected){
            countDownLatch.countDown();

        }
        else if (event.getType() == Event.EventType.NodeCreated) {
            log.info("node create={}", event.getPath() );
        }
        else if (event.getType() == Event.EventType.NodeDeleted) {
            log.info("node delete={}", event.getPath() );
        }if (event.getType() == Event.EventType.NodeDataChanged) {
            String data = readData(event.getPath());
            log.info("data change. path={}, data={}", event.getPath(), data);
        }

        //必须重新注册，要不然就无法获得变化通知
        try {
            zooKeeper.exists(PATH_NAME, this);
        }catch (Exception ex) {
            log.error( "Failed to connect, Exception , ex={}", ex.getMessage(), ex );
        }
    }

    public void connect(String hosts){
        try {
            if(zooKeeper == null){
                zooKeeper = new ZooKeeper(hosts,SESSION_TIME,this);
                zooKeeper.exists(PATH_NAME, this);
                countDownLatch.await();
            }
        } catch (IOException ex) {
            log.error("Failed to connect, IOException , ex={} ", ex.getMessage(), ex);
        } catch (InterruptedException ex) {
            log.error( "Failed to connect, InterruptedException , ex={}", ex.getMessage(), ex );
        } catch (Exception ex) {
            log.error( "Failed to connect, Exception , ex={}", ex.getMessage(), ex );
        }
    }


    public void close(){
        try {
            if(zooKeeper != null){
                zooKeeper.close();
            }
        } catch (InterruptedException ex) {
            log.error("release connection error={}", ex.getMessage() ,ex);
        }
    }

    public boolean createPath(String path, String data){
        try {
            String zkPath = MyZooKeeper.zooKeeper.create(path, data.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            log.info("ZooKeeper. create path={}", zkPath);
            return true;
        } catch (KeeperException e) {
            log.error("Failed to create path. errMsg：" + e.getMessage() + "，path:" + path  ,e);
        } catch (InterruptedException e) {
            log.error("Failed to create path. errMsg:" + e.getMessage() + "，path:" + path  ,e);
        }
        return false;
    }
    public boolean detelePath(String path){
        try {
            MyZooKeeper.zooKeeper.delete(path, -1);
            log.info("ZooKeeper delete path，path={}", path);
            return true;
        } catch (InterruptedException e) {
            log.error("Failed to delete path, errMsg：" + e.getMessage() + "，path:" + path ,e);
        } catch (KeeperException e) {
            log.error("Failed to delete path, errMsg：" + e.getMessage() + "，path:" + path  ,e);
        }
        return false;
    }

    public String readData(String path ){
        String data = null;
        try {
            data = new String( MyZooKeeper.zooKeeper.getData( path, false, null ) );
            log.info( "read data. path={}, content={}", path, data);
        } catch (KeeperException e) {
            log.error("Failed to read data. zKException!.", path, e.getMessage());
        } catch (InterruptedException e) {
            log.error("Failed to read data. 发生InterruptedException!. path={}, exMsg={}", path, e.getMessage());
        }
        return  data;
    }
}

main函数。这是个简单的示例程序，因此我在主函数使用 Thread.sleep(1000 * 120); 让用户有机会通过zkCli命令行工具，对zk的数据进行变更。

package com.yq;

import com.yq.service.MyZooKeeper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Simple to Introduction
 * className: ZKDemoOneApplication
 *
 * @author EricYang
 * @version 2018/8/24 23:43
 */

public class ZKClientApp {
    private static final Logger log = LoggerFactory.getLogger(ZKClientApp.class);
    private static final String ZK_SERVERS = "127.0.0.1:2181";
    private static final String PATH_NAME_TEST = "/test001";

    public static void main(String[] args) {

        MyZooKeeper zk = new MyZooKeeper();
        zk.connect(ZK_SERVERS);
        zk.createPath(PATH_NAME_TEST, "hello world!");
        String value = zk.readData(PATH_NAME_TEST);
        log.info("znode={}, data={}", PATH_NAME_TEST, value);
        zk.detelePath(PATH_NAME_TEST);
        try {
            Thread.sleep(1000 * 120);
        }
        catch (Exception ex){
            log.info("start ex={}.", ex);
        }

        log.info("start done.");
    }
}

3，截图

通过截图可以的看到，当我们对/yqPath的数据进行变更时，程序得到了通知
这里写图片描述

ZooKeeper Java API学习笔记（一）

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