zookeeper客户端使用与集群特性

zookeeper客户端使用与集群特性

• zookeeper Java客户端
• • 项目构建
  • 创建客户端实例
  • 测试结果
  • 创建zookeeper实例参数说明
  • 演示java客户端增删查改zookeeper节点
• Apache Curator 开源客户端
• • 什么是 Curator
  • Curator 实战
  • • 会话创建
    • 创建节点
    • 异步接口
• zookeeper集群&不停机动态扩容/缩容
• • zookeeper集群搭建

zookeeper Java客户端 项目构建

zookeeper 官方的客户端没有和服务端代码分离，他们为同一个jar 文件，所以我们直接引入 zookeeper的maven即可， 这里版本请保持与服务端版本一致，不然会有很多兼容性的问题

    org.apache.zookeeper
    zookeeper
    3.5.8

创建客户端实例

• 定义要发送的包装类

package zookeeper.client;


import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

@Data
@ToString
@NoArgsConstructor
public class MyConfig {
    private String key;
    private String name;
}

• 定义zookeeper客户端

package zookeeper.client;

import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.SneakyThrows;
import lombok.extern.slf4j.Slf4j;
import org.apache.zookeeper.*;

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

@Slf4j
public class ConfigCenter {

    private final static  String CONNECT_STR="192.168.1.104:2181";
    private final static Integer  SESSION_TIMEOUT=30*1000;
    private static ZooKeeper zooKeeper=null;

    private static CountDownLatch countDownLatch=new CountDownLatch(1);

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        zooKeeper=new ZooKeeper(CONNECT_STR, SESSION_TIMEOUT, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                    if (event.getType()== Event.EventType.None
                            && event.getState() == Event.KeeperState.SyncConnected){
                        log.info("连接已建立");
                        countDownLatch.countDown();
                    }
            }
        });
        countDownLatch.await();


        MyConfig myConfig = new MyConfig();
        myConfig.setKey("anykey");
        myConfig.setName("anyName");

        ObjectMapper objectMapper=new ObjectMapper();

        byte[] bytes = objectMapper.writevalueAsBytes(myConfig);

        String s = zooKeeper.create("/myconfig", bytes, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

        Watcher watcher = new Watcher() {
            @SneakyThrows
            @Override
            public void process(WatchedEvent event) {
                if (event.getType()== Event.EventType.NodeDataChanged
                        && event.getPath()!=null && event.getPath().equals("/myconfig")){
                    log.info(" PATH:{}  发生了数据变化" ,event.getPath());

                    byte[] data = zooKeeper.getData("/myconfig", this, null);

                    MyConfig newConfig = objectMapper.readValue(new String(data), MyConfig.class);

                    log.info("数据发生变化: {}",newConfig);

                }


            }
        };

        byte[] data = zooKeeper.getData("/myconfig", watcher, null);
        MyConfig originalMyConfig = objectMapper.readValue(new String(data), MyConfig.class);
        log.info("原始数据: {}", originalMyConfig);


        TimeUnit.SECONDS.sleep(Integer.MAX_VALUE);
    }
}

• log4j.properties配置类

# Copyright 2012 The Apache Software Foundation
# 
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR ConDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Define some default values that can be overridden by system properties
zookeeper.root.logger=ERROR, ConSOLE

zookeeper.console.threshold=INFO
zookeeper.log.dir=.
zookeeper.log.file=zookeeper.log
zookeeper.log.threshold=INFO
zookeeper.log.maxfilesize=256MB
zookeeper.log.maxbackupindex=20

zookeeper.tracelog.dir=${zookeeper.log.dir}
zookeeper.tracelog.file=zookeeper_trace.log

log4j.rootLogger=${zookeeper.root.logger}

#
# console
# Add "console" to rootlogger above if you want to use this 
#
log4j.appender.ConSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n

#
# Add ROLLINGFILE to rootLogger to get log file output
#
log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}
log4j.appender.ROLLINGFILE.MaxFileSize=${zookeeper.log.maxfilesize}
log4j.appender.ROLLINGFILE.MaxBackupIndex=${zookeeper.log.maxbackupindex}
log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n

#
# Add TRACEFILE to rootLogger to get log file output
#    Log TRACE level and above messages to a log file
#
log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
log4j.appender.TRACEFILE.Threshold=TRACE
log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}

log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
### Notice we are including log4j's NDC here (%x)
log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n
log4j.logger.zookeeper.client=INFO

测试结果

创建zookeeper实例参数说明

参数名称	含义
connectString	ZooKeeper服务器列表，由英文逗号分开的host:port字符串组成， 每一个都代表一台ZooKeeper机器，如， host1:port1,host2:port2,host3:port3。另外，也可以在connectString中设置客户端连接上ZooKeeper 后的根目录，方法是在host:port字符串之后添加上这个根目录，例 如,host1:port1,host2:port2,host3:port3/zk-base,这样就指定了该客户端连 接上ZooKeeper服务器之后,所有对ZooKeeper 的操作，都会基于这个根目录。例如，客户端对/sub-node 的操作，最终创建 /zk-node/sub-node, 这个目录也叫Chroot，即客户端隔离命名空间。
sessionTimeout	会话的超时时间，是一个以“毫秒”为单位的整型值。在ZooKeeper中有会话的概念，在一个会话周期内，ZooKeeper客户端和服务器之间会通过心跳 检测机制来维持会话的有效性，一旦在sessionTimeout时间内没有进行有效 的心跳检测，会话就会失效。
watcher	ZooKeeper允许 客户端在构造方法中传入一个接口 watcher (org.apache. zookeeper. Watcher)的实现类对象来作为默认的Watcher事件通知处理器。当然，该参 数可以设置为null 以表明不需要设置默认的 Watcher处理器。
canBeReadOnly	这是一个boolean类型的参数，用于标识当前会话是否支持“read-only(只 读)”模式。默认情况下，在ZooKeeper集群中，一个机器如果和集群中过半及以上机器失去了网络连接，那么这个机器将不再处理客户端请求（包括读写请求)。但是在某些使用场景下，当ZooKeeper服务器发生此类故障的时候，我 们还是希望ZooKeeper服务器能够提供读服务（当然写服务肯定无法提供）—— 这就是 ZooKeeper的“read-only”模式。
sessionId和 sessionPasswd	分别代表会话ID和会话秘钥。这两个参数能够唯一确定一个会话，同时客户端使用这两个参数可以实现客户端会话复用，从而达到恢复会话的效果。具体使用方法是，第一次连接上ZooKeeper服务器时，通过调用ZooKeeper对象实例的以下两个接口，即可获得当前会话的ID和秘钥: long getSessionId(); byte[]getSessionPasswd( ); 荻取到这两个参数值之后，就可以在下次创建ZooKeeper对象实例的时候传入构造方法了

演示java客户端增删查改zookeeper节点

package zookeeper.client;


import lombok.extern.slf4j.Slf4j;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.junit.After;
import org.junit.Before;

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

@Slf4j
public abstract class Standalonebase {

    private static final String CONNECT_STR = "192.168.1.104:2181";

    private static final int SESSION_TIMEOUT = 30 * 1000;

    private static ZooKeeper zooKeeper = null;

    private static CountDownLatch countDownLatch = new CountDownLatch(1);

    private Watcher watcher = new Watcher() {
        @Override
        public void process(WatchedEvent event) {
            if (event.getState() == Event.KeeperState.SyncConnected
                    && event.getType() == Event.EventType.None) {
                countDownLatch.countDown();
                log.info("连接建立");
            }
        }
    };


    @Before
    public void init() {
        try {
            log.info(" start to connect to zookeeper server: {}", getConnectStr());
            zooKeeper = new ZooKeeper(getConnectStr(), getSessionTimeout(), watcher);
            log.info(" 连接中...");
            countDownLatch.await();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }


    public static ZooKeeper getZooKeeper() {
        return zooKeeper;
    }


    @After
    public void test() {
        try {
            TimeUnit.SECONDS.sleep(Integer.MAX_VALUE);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }


    protected String getConnectStr() {
        return CONNECT_STR;
    }

    protected int getSessionTimeout() {
        return SESSION_TIMEOUT;
    }
}

package zookeeper.client;

import lombok.extern.slf4j.Slf4j;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Id;
import org.apache.zookeeper.server.auth.DigestAuthenticationProvider;
import org.junit.Test;

import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;

@Slf4j
public class AclOperations extends Standalonebase {
    
    @Test
    public void createWithAclTest1() throws KeeperException, InterruptedException {

        List acLList = new ArrayList();
        ACL e = new ACL();
        Id m_ = new Id();
        m_.setId("anyone");
        m_.setScheme("world");

        int perms = ZooDefs.Perms.ADMIN  |  ZooDefs.Perms.READ;
        e.setId(m_);
        e.setPerms(perms);
        acLList.add(e);
        String s = getZooKeeper().create("/zk-node-1", "shikaiqiang".getBytes(), acLList, CreateMode.PERSISTENT);
        log.info("create path: {}",s);
    }

    
    @Test
    public void createWithAclTest2() throws KeeperException, InterruptedException {

        // 对连接添加授权信息
        getZooKeeper().addAuthInfo("digest","u400:p400".getBytes());

        List acLList = new ArrayList();
        ACL e = new ACL();
        Id m_ = new Id();
        m_.setId("u400:p400");
        m_.setScheme("auth");

        int perms = ZooDefs.Perms.ADMIN  |  ZooDefs.Perms.READ;
        e.setId(m_);
        e.setPerms(perms);
        acLList.add(e);

        String s = getZooKeeper().create("/zk-node-2", "shikaiqiang".getBytes(), acLList, CreateMode.PERSISTENT);
        log.info("create path: {}",s);
    }


    @Test
    public void createWithAclTest3() throws KeeperException, InterruptedException {

        // 对连接添加授权信息
        getZooKeeper().addAuthInfo("digest","u400:p400".getBytes());


        byte[] data = getZooKeeper().getData("/test", false, null);

        log.info("GET_data: {}",new String(data));
    }


    public static void main(String[] args) throws NoSuchAlgorithmException {
        String sId = DigestAuthenticationProvider.generateDigest("skq:123456");
        System.out.println(sId);
        //  -Dzookeeper.DigestAuthenticationProvider.superDigest=gj:X/NSthOB0fD/OT6iilJ55WJVado=
    }
}

package zookeeper.client;

import lombok.extern.slf4j.Slf4j;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import org.junit.Test;

@Slf4j
public class baseOperations extends Standalonebase {

    private String first_node = "/first-node";

    @Test
    public void testCreate() throws KeeperException, InterruptedException {
        ZooKeeper zooKeeper = getZooKeeper();

        String s = zooKeeper.create(first_node, "first".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        log.info("Create:{}", s);
    }

    @Test
    public void testGetData() {

        Watcher watcher = new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                if (event.getPath() != null && event.getPath().equals(first_node)
                        && event.getType() == Event.EventType.NodeDataChanged) {
                    log.info(" PATH: {}  发现变化", first_node);
                    try {
                        byte[] data = getZooKeeper().getData(first_node, this, null);
                        log.info(" data: {}", new String(data));
                    } catch (KeeperException e) {
                        e.printStackTrace();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        try {
            byte[] data = getZooKeeper().getData(first_node, watcher, null);  //
            log.info(" data: {}", new String(data));
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

    @Test
    public void testSetData() throws KeeperException, InterruptedException {
        ZooKeeper zooKeeper = getZooKeeper();


        Stat stat = new Stat();
        byte[] data = zooKeeper.getData(first_node, false, stat);
        // int version = stat.getVersion();
        zooKeeper.setData(first_node, "third".getBytes(), 0);


    }


    @Test
    public void testDelete() throws KeeperException, InterruptedException {
        // -1 代表匹配所有版本，直接删除
        // 任意大于 -1 的代表可以指定数据版本删除
        getZooKeeper().delete(first_node, -1);

    }

    @Test
    public void asyncTest() {
        String userId = "xxx";
        getZooKeeper().getData("/test", false, (rc, path, ctx, data, stat) -> {
            Thread thread = Thread.currentThread();

            log.info(" Thread Name: {},   rc:{}, path:{}, ctx:{}, data:{}, stat:{}", thread.getName(), rc, path, ctx, data, stat);
        }, "test");
        log.info(" over .");

    }


}

Apache Curator 开源客户端 什么是 Curator

Curator 是一套由netflix 公司开源的，Java 语言编程的 ZooKeeper 客户端框架，Curator项目是现在ZooKeeper 客户端中使用最多，对ZooKeeper 版本支持最好的第三方客户端，并推荐使用，Curator 把我们平时常用的很多 ZooKeeper服务开发功能做了封装，例如 Leader 选举、 分布式计数器、分布式锁。这就减少了技术人员在使用 ZooKeeper 时的大部分底层细节开发工 作。在会话重新连接、Watch 反复注册、多种异常处理等使用场景中，用原生的 ZooKeeper 处理比较复杂。而在使用 Curator 时，由于其对这些功能都做了高度的封装，使用起来更加简单，不但减少了开发时间，而且增强了程序的可靠性。

Curator 实战

首先要引入Curator 框架相关的开发包，第一个是 curator-framework 包，该包是对 ZooKeeper 底层 API 的一 些封装。另一个是 curator-recipes 包，该包封装了一些 ZooKeeper 服务的高级特性，如： Cache 事件监听、选举、分布式锁、分布式 Barrier。为了方便测试引入 了junit ，lombok，由于Zookeeper本身以来了 log4j 日志框架，所以这里可以创建对应的 log4j配置文件后直接使用。

    org.apache.curator
    curator-recipes
    5.0.0
    
        
            org.apache.zookeeper
            zookeeper
        
    


    org.apache.curator
    curator-x-discovery
    5.0.0
    
        
            org.apache.zookeeper
            zookeeper
        
    


    org.apache.zookeeper
    zookeeper
    3.5.8


    junit
    junit
    4.13


    org.projectlombok
    lombok
    1.18.12


    com.fasterxml.jackson.core
    jackson-databind
    2.8.3

会话创建

要进行客户端服务器交互，第一步就要创建会话 Curator 提供了多种方式创建会话，比如用静态工厂方式创建：

// 重试策略 
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3) 
Curatorframework client = CuratorframeworkFactory.newClient(zookeeperConnectionString, retryPolicy);
client.start();

RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3); 
Curatorframework client = CuratorframeworkFactory.builder() 
 .connectString("192.168.1.104:2181") 
 .sessionTimeoutMs(5000) // 会话超时时间 
 .connectionTimeoutMs(5000) // 连接超时时间 
 .retryPolicy(retryPolicy) 
 .namespace("base") // 包含隔离名称 
 .build(); 
client.start();

这段代码的编码风格采用了流式方式，最核心的类是 Curatorframework 类，该类的作用是定 义一个 ZooKeeper 客户端对象，并在之后的上下文中使用。在定义 Curatorframework 对象 实例的时候，我们使用了 CuratorframeworkFactory 工厂方法，并指定了 connectionString 服务器地址列表、retryPolicy 重试策略 、sessionTimeoutMs 会话超时时间、 connectionTimeoutMs 会话创建超时时间。

connectionString：服务器地址列表，在指定服务器地址列表的时候可以是一个地址，也可以 是多个地址。如果是多个地址，那么每个服务器地址列表用逗号分隔, 如 host1:port1,host2:port2,host3；port3 。

retryPolicy：重试策略，当客户端异常退出或者与服务端失去连接的时候，可以通过设置客户端重新连接 ZooKeeper 服务端。而 Curator 提供了 一次重试、多次重试等不同种类的实现方式。在 Curator 内部，可以通过判断服务器返回的 keeperException 的状态代码来判断是否进行重试处理，如果返回的是 OK 表示一切操作都没有问题，而 SYSTEMERROR 表示系统或服务端错误。

策略名称	描述
ExponentialBackoffRetry	重试一组次数，重试之间的睡眠时间增加
RetryNTimes	重试最大次数
RetryOneTime	只重试一次
RetryUntilElapsed	在给定的时间结束之前重试

超时时间：Curator 客户端创建过程中，有两个超时时间的设置。一个是 sessionTimeoutMs 会话超时时间，用来设置该条会话在 ZooKeeper 服务端的失效时间。另一个是 connectionTimeoutMs 客户端创建会话的超时时间，用来限制客户端发起一个会话连接到接收 ZooKeeper 服务端应答的时间。sessionTimeoutMs 作用在服务端，而 connectionTimeoutMs 作用在客户端。

创建节点

在 Curator 中，可以使用 create 函数创建数据节点，并通过 withMode 函数指定节点类型 （持久化节点，临时节点，顺序节点，临时顺序节点，持久化顺序节点等），默认是持久化节点，之后调用 forPath 函数来指定节点的路径和数据信息

guaranteed：该函数的功能如字面意思一样，主要起到一个保障删除成功的作用，其底层工作方式是：只要该客户端的会话有效，就会在后台持续发起删除请求，直到该数据节点在 ZooKeeper 服务端被删除。

deletingChildrenIfNeeded：指定了该函数后，系统在删除该数据节点的时候会以递归的方式直接删除其子节点，以及子节点的子节点。

package zookeeper.curator;

import lombok.extern.slf4j.Slf4j;
import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.Curatorframework;
import org.apache.curator.framework.CuratorframeworkFactory;
import org.apache.curator.framework.state.ConnectionState;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.zookeeper.data.Stat;
import org.junit.After;
import org.junit.Before;

import java.util.concurrent.TimeUnit;

@Slf4j
public abstract class CuratorStandalonebase {

    private static final String CONNECT_STR = "192.168.1.104:2181";
    private static final int sessionTimeoutMs = 60 * 1000;
    private static final int connectionTimeoutMs = 5000;
    private static Curatorframework curatorframework;

    @Before
    public void init() {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(5000, 30);
        curatorframework = CuratorframeworkFactory.builder().connectString(getConnectStr())
                .retryPolicy(retryPolicy)
                .sessionTimeoutMs(sessionTimeoutMs)
                .connectionTimeoutMs(connectionTimeoutMs)
                .canBeReadOnly(true)
                .build();
        curatorframework.getConnectionStateListenable().addListener((client, newState) -> {
            if (newState == ConnectionState.CONNECTED) {
                log.info("连接成功！");
            }

        });
        log.info("连接中......");
        curatorframework.start();
    }

    public void createIfNeed(String path) throws Exception {
        Stat stat = curatorframework.checkExists().forPath(path);
        if (stat == null) {
            String s = curatorframework.create().forPath(path);
            log.info("path {} created! ", s);
        }
    }

    public static Curatorframework getCuratorframework() {
        return curatorframework;
    }

    @After
    public void test() {
        try {
            TimeUnit.SECONDS.sleep(Integer.MAX_VALUE);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }


    protected String getConnectStr() {
        return CONNECT_STR;
    }
}

创建节点的方式如下面的代码所示，回顾我们之前课程中讲到的内容，描述一个节点要包括节点 的类型，即临时节点还是持久节点、节点的数据信息、节点是否是有序节点等属性和性质。

package zookeeper.curator;

import lombok.extern.slf4j.Slf4j;
import org.apache.curator.framework.Curatorframework;
import org.apache.zookeeper.CreateMode;
import org.junit.Test;

import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Slf4j
public class CuratorbaseOperations extends CuratorStandalonebase {


    // 递归创建子节点
    @Test
    public void testCreateWithParent() throws Exception {
        Curatorframework curatorframework = getCuratorframework();

        String pathWithParent = "/node-parent/sub-node-1";
        String path = curatorframework.create().creatingParentsIfNeeded().forPath(pathWithParent);
        log.info("curator create node :{}  successfully.", path);
    }


    // protection 模式，防止由于异常原因，导致僵尸节点
    @Test
    public void testCreate() throws Exception {

        Curatorframework curatorframework = getCuratorframework();
        String forPath = curatorframework
                .create()
                .withProtection()
                .withMode(CreateMode.EPHEMERAL_SEQUENTIAL).
                        forPath("/curator-node", "some-data".getBytes());
        log.info("curator create node :{}  successfully.", forPath);


    }

    @Test
    public void testGetData() throws Exception {
        Curatorframework curatorframework = getCuratorframework();

        byte[] bytes = curatorframework.getData().forPath("/test");
        log.info("get data from  node :{}  successfully.", new String(bytes));
    }


    @Test
    public void testSetData() throws Exception {
        Curatorframework curatorframework = getCuratorframework();

        curatorframework.setData().forPath("/test", "changed!".getBytes());
        byte[] bytes = curatorframework.getData().forPath("/test");
        log.info("get data from  node /curator-node :{}  successfully.", new String(bytes));
    }

    @Test
    public void testDelete() throws Exception {
        Curatorframework curatorframework = getCuratorframework();

        String pathWithParent = "/node-parent";
        curatorframework.delete().guaranteed().deletingChildrenIfNeeded().forPath(pathWithParent);
    }

    @Test
    public void testListChildren() throws Exception {
        Curatorframework curatorframework = getCuratorframework();

        String pathWithParent = "/node-parent";
        List strings = curatorframework.getChildren().forPath(pathWithParent);
        strings.forEach(System.out::println);
    }
}

异步接口

Curator 引入了BackgroundCallback 接口，用来处理服务器端返回来的信息，这个处理过程是 在异步线程中调用，默认在 EventThread 中调用，也可以自定义线程池。

public interface BackgroundCallback
{
    
    public void processResult(Curatorframework client, CuratorEvent event) throws Exception;
}

如上接口，主要参数为client 客户端 和服务端事件event

inBackground 异步处理默认在EventThread中执行，指定线程池

@Test
public void testThreadPool() throws Exception {

    Curatorframework curatorframework = getCuratorframework();
    ExecutorService executorService = Executors.newSingleThreadExecutor();
    String ZK_NODE = "/zk-node";
    curatorframework.getData().inBackground((client, event) -> {
        log.info(" background: {}", event);
    }, executorService).forPath(ZK_NODE);

}

zookeeper集群&不停机动态扩容/缩容

zookeeper集群模式一共有三种类型的角色

• Leader： 处理所有的事务请求（写请求），可以处理读请求，集群中只能有一个Leader
• Follower：只能处理读请求，同时作为 Leader的候选节点，即如果Leader宕机，Follower要参与到新的Leader选举中，有可能成为新的Leader节点。
• Observer：只能处理读请求。不能参与选举

zookeeper集群搭建

配置zoo1.cfg文件

分别配置zoo1.cfg,zoo2.cfg,zoo3.cfg,zoo4.cfg

启动4个zookeeper实例

连接实例

bin/zkCli.sh -server 192.168.1.104:2181,192.168.1.104:2182,192.168.1.104:2183,192.168.1.104:2184

public static void main(String[] args) throws Exception {


        RetryPolicy retryPolicy=new ExponentialBackoffRetry( 5*1000, 10 );

        String connectStr = "192.168.1.104:2181,192.168.1.104:2182,192.168.1.104:2183,192.168.1.104:2184";
        Curatorframework curatorframework = CuratorframeworkFactory.newClient(connectStr, retryPolicy);
        curatorframework.start();



        String pathWithParent = "/test";
        byte[] bytes = curatorframework.getData().forPath(pathWithParent);
        System.out.println(new String(bytes));
        while (true) {

            try {
                byte[] bytes2 = curatorframework.getData().forPath(pathWithParent);
                System.out.println(new String(bytes2));

                TimeUnit.SECONDS.sleep(5);
            } catch (Exception e) {
                e.printStackTrace();
             }

        }
    }