zookeeper实现的简单选主

用户服务

package com.demo.local.zookeeper;

import lombok.Data;

import java.io.Serializable;

/**
 * @author ryan
 * @since 2019/08/21
 **/
@Data
public class UserCenter implements Serializable {

    private Integer id;

    private String name;
}

选主器

package com.demo.local.zookeeper;

import com.sun.istack.internal.NotNull;
import lombok.Data;
import lombok.NonNull;
import org.I0Itec.zkclient.IZkDataListener;
import org.I0Itec.zkclient.IZkStateListener;
import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.exception.ZkException;
import org.I0Itec.zkclient.exception.ZkNodeExistsException;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.Watcher;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * @author ryan
 * @since 2019/08/21
 **/
@Data
public class MasterSelector {

    @NonNull
    private ZkClient zkClient;

    @NonNull
    private UserCenter userCenter;

    private UserCenter master;

    private Boolean isRunning = false;

    private ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);

    private static final String MASTER_PATH = "/master";


    public void start() {
        if (isRunning) {
            return;
        }
        chooseMaster();
        isRunning = true;
    }


    private void chooseMaster() {
        try {
            if (userCenter != master) {
                System.out.println(userCenter.getName() + ":争抢master");
                zkClient.createEphemeral(MASTER_PATH, userCenter);
                master = userCenter;
                System.out.println(userCenter.getName() + ":现在我是master");
               // 通过定时器，释放节点，模拟主节点丢失场景
                executorService.schedule(() -> releaseMaster(), 1, TimeUnit.SECONDS);
            }
        } catch (ZkNodeExistsException e) {
           // 如果主节点已存在，则监听主节点的数据变化，若主节点丢失，则开始选主
            zkClient.subscribeDataChanges(MASTER_PATH, new IZkDataListener() {
                @Override
                public void handleDataChange(String s, Object o) throws Exception {

                }
                @Override
                public void handleDataDeleted(String s) throws Exception {
                    System.out.println(userCenter.getName() + ":master消失");
                    chooseMaster();
                }
            });
        }
    }

    private void releaseMaster() {
        UserCenter data = zkClient.readData(MASTER_PATH, true);
        if (data != null && userCenter.getId().equals(data.getId())) {
            zkClient.delete(MASTER_PATH, -1);
            System.out.println(userCenter.getName() + ":现在没有master");
        }
        master = null;
    }

}

运行代码

package com.demo.local.zookeeper;

import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.serialize.SerializableSerializer;
import org.I0Itec.zkclient.serialize.ZkSerializer;

import java.sql.Time;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * @author ryan
 * @since 2019/08/21
 **/
public class MasterTest {

    public static void main(String[] args) throws InterruptedException {
        String address = "localhost:2181";
        CountDownLatch latch = new CountDownLatch(10);
        for (int i = 0; i < 10; i++) {
            UserCenter userCenter = new UserCenter();
            userCenter.setId(i);
            userCenter.setName("用户服务:" + i);

            ZkClient client = new ZkClient(address, 5000, 10000, new SerializableSerializer());

            ExecutorService executorService = Executors.newFixedThreadPool(10);

            MasterSelector selector = new MasterSelector(client, userCenter);

            executorService.submit(() -> {
                try {
                    latch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                selector.start();

            });
            latch.countDown();
        }
    }
}