分布式框架Zookeeper api的使用介绍

2022-11-13 16:11:13 分布式框架介绍

前言

ZooKeeper api共包含五个包，分别为：

org.apache.zookeeper
org.apache.zookeeper.data
org.apache.zookeeper.server
org.apache.zookeeper.server.quorum
org.apache.zookeeper.server.upgrade

其中org.apache.zookeeper，包含Zookeeper类，他是我们编程时最常⽤的类文件。这个类是Zookeeper客户端的主要类文件。如果要使用Zookeeper服务，应⽤程序⾸先必须创建⼀个Zookeeper实例，这时就需要使用此类。⼀旦客户端和Zookeeper服务端建立起了连接，Zookeeper系统将会给本次连接会话分配⼀个ID值，并且客户端将会周期性的向服务器端发送心跳来维持会话连接。只要连接有效，客户端就可以使⽤Zookeeper API来做相应处理了

导入依赖

<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.4.14</version>
</dependency>

建立会话

package com.laGou.api;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import java.io.IOException;
import java.util.concurrent.CountDownLatch;
public class CreateSession implements Watcher {
    private static CountDownLatch countDownLatch = new CountDownLatch(1);
    
    public static void main(String[] args) throws IOException, InterruptedException {
        
        ZooKeeper zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new CreateSession());
        System.out.println(zooKeeper.getState());
        // 计数工具类 CountDownLatch : 不让main方法结束，让线程处于等待阻塞
        countDownLatch.await();
        System.out.println("客户端与服务端会话真正建立了");
    }
    
    // 当前类实现了Watcher接⼝，重写了process⽅法，该⽅法负责处理来⾃Zookeeper服务端的watcher通知，在收到服务端发送过来的SyncConnected事件之后，解除主程序在CountDownLatch上的等待阻塞，⾄此，会话创建完毕
    public void process(WatchedEvent watchedEvent) {
        //当连接创建了，服务端发送给客户端SyncConnected事件
        if(watchedEvent.getState() == Event.KeeperState.SyncConnected) {
            // 解除主程序在CountDownLatch上的等待阻塞
            countDownLatch.countDown();
        }
    }
}

注意，ZooKeeper 客户端和服务端会话的建立是⼀个异步的过程，也就是说在程序中，构造⽅法会在处理完客户端初始化工作后立即返回，在⼤多数情况下，此时并没有真正建立好⼀个可用的会话，在会话的生命周期中处于“CONNECTING”的状态。当该会话真正创建完毕后ZooKeeper服务端会向会话对应的客户端发送⼀个事件通知，以告知客户端，客户端只有在获取这个通知之后，才算真正建立了会话。

创建节点

package com.lagou.api;
import org.apache.zookeeper.*;
import java.io.IOException;
import java.util.concurrent.CountDownLatch;
public class CreateNote implements Watcher {
    private static ZooKeeper zooKeeper;
    
    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        
        zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new CreateNote());
        System.out.println(zooKeeper.getState());
        Thread.sleep(Integer.MAX_VALUE);
    }
    // 创建节点的方法
    private static void createNoteSync() throws InterruptedException, KeeperException {
        
        // 持久节点
        String note_persistent = zooKeeper.create("/lg-persistent", "持久节点内容".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        // 临时节点
        String note_ephemeral = zooKeeper.create("/lg-ephemeral", "临时节点内容".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        // 持久顺序节点
        String note_sequential = zooKeeper.create("/lg-sequential", "持久顺序节点内容".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT_SEQUENTIAL);
        System.out.println("创建的持久节点: " + note_persistent);
        System.out.println("创建的临时节点: " + note_ephemeral);
        System.out.println("创建的持久顺序节点: " + note_sequential);
    }
    
    public void process(WatchedEvent watchedEvent) {
        // SyncConnected
        if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
            // 创建节点
            try {
                createNoteSync();
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }
}

获取节点数据

package com.lagou.api;
import org.apache.zookeeper.*;
import java.io.IOException;
import java.util.List;
public class GetNoteData implements Watcher {
    private static ZooKeeper zooKeeper;
    
    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        
        zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new GetNoteData());
        System.out.println(zooKeeper.getState());
        Thread.sleep(Integer.MAX_VALUE);
    }
    
    public void process(WatchedEvent watchedEvent) {
        
        if (watchedEvent.getType() == Event.EventType.nodeChildrenChanged) {
            List<String> children = null;
            try {
                children = zooKeeper.getChildren("/lg-persistent", true);
            } catch (KeeperException | InterruptedException e) {
                throw new RuntimeException(e);
            }
            System.out.println(children);
        }
        // SyncConnected
        if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
            // 获取节点数据的方法
            try {
                getNoteData();
                // 获取节点的子节点列表方法
                getChildren();
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }
    
    private void getNoteData() throws Exception {
        
        byte[] data = zooKeeper.getData("/lg-persistent", false, null);
        System.out.println(new String(data));
    }
    
    public static void getChildren() throws InterruptedException, KeeperException {
        
        List<String> children = zooKeeper.getChildren("/lg-persistent", true);
        System.out.println(children);
    }
}

修改节点数据

package com.lagou.api;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import java.io.IOException;
public class UpdateNoteData implements Watcher {
    private static ZooKeeper zooKeeper;
    
    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        
        zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new UpdateNoteData());
        System.out.println(zooKeeper.getState());
        Thread.sleep(Integer.MAX_VALUE);
    }
    
    public void process(WatchedEvent watchedEvent) {
        // SyncConnected
        if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
            // 更新数据节点内容的方法
            try {
                updateNoteSync();
            } catch (InterruptedException | KeeperException e) {
                throw new RuntimeException(e);
            }
        }
    }
    
    private void updateNoteSync() throws InterruptedException, KeeperException {
        
        byte[] data = zooKeeper.getData("/lg-persistent", false, null);
        System.out.println("修改前的值：" + new String(data));
        // 修改 /lg-persistent 的数据    stat: 状态信息对象
        Stat stat = zooKeeper.setData("/lg-persistent", "客户端修改了节点数据".getBytes(), -1);
        byte[] data2 = zooKeeper.getData("/lg-persistent", false, null);
        System.out.println("修改后的值：" + new String(data2));
    }
}

删除节点

package com.lagou.api;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
import java.io.IOException;
public class DeleteNote implements Watcher {
    private static ZooKeeper zooKeeper;
    
    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
        
        zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new DeleteNote());
        System.out.println(zooKeeper.getState());
        Thread.sleep(Integer.MAX_VALUE);
    }
    
    public void process(WatchedEvent watchedEvent) {
        // SyncConnected
        if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
            // 删除节点
            try {
                deleteNoteSync();
            } catch (InterruptedException | KeeperException e) {
                throw new RuntimeException(e);
            }
        }
    }
    
    private void deleteNoteSync() throws InterruptedException, KeeperException {
        
        Stat stat = zooKeeper.exists("/lg-persistent/c1", false);
        System.out.println(stat == null ? "该节点不存在" : "该节点存在");
        if (stat != null) {
            zooKeeper.delete("/lg-persistent/c1", -1);
        }
        Stat stat2 = zooKeeper.exists("/lg-persistent/c1", false);
        System.out.println(stat2 == null ? "该节点不存在" : "该节点存在");
    }
}

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