zookeeper_demo

参考：全网最详细的zookeeper实战教程，看完你就知道有多值 - 知乎 (zhihu.com)

ZooKeeper入门，看这篇就够了！ - 知乎 (zhihu.com)

windows安装zk：windows环境下安装zookeeper教程详解（单机版）_风轩雨墨的博客-CSDN博客 

zk的watch机制：Zookeeper——Watch机制原理_zookeeper watch机制_庄小焱的博客-CSDN博客

命令行使用zk：

 

javaAPI使用zk：

znode增删改查demo：

CRUDMain.java

package com.hmb;

import org.apache.zookeeper.*;

import java.io.IOException;

public class CRUDMain {
    public static void main(String[] args) throws InterruptedException, KeeperException, IOException {
        String SERVER_HOST = "127.0.0.1:2181";
        int SESSION_TIME_OUT = 2000;
        ZooKeeper zooKeeper = new ZooKeeper(SERVER_HOST, SESSION_TIME_OUT, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                Event.KeeperState state = watchedEvent.getState();
                if (state == Event.KeeperState.SyncConnected) {
                    Event.EventType type = watchedEvent.getType();
                    if (type == Event.EventType.None) {
                        System.out.println("zk client connect server successfully...");
                    }
                }
            }
        });

        String path = "/java";
        zooKeeper.create(path, "HelloWorld".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        System.out.println("add znode successfully.");
        System.out.println(new String(zooKeeper.getData(path, false, null)));
        zooKeeper.setData(path, "hhhh".getBytes(), -1);
        System.out.println(new String(zooKeeper.getData(path, false, null)));
        zooKeeper.delete(path, -1);
        System.out.println(zooKeeper.exists(path, false));
        zooKeeper.close();
    }
}

　　

运行结果：

 

服务器上下线动态感知demo：

ZkClient.java

package com.hmb;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

import java.io.IOException;
import java.util.LinkedList;
import java.util.List;

public class ZkClient {
    private static ZooKeeper zooKeeper;
    private static String path = "/";
    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
         zooKeeper = new ZooKeeper("127.0.0.1:2181", 5000, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                if (event.getType() == Event.EventType.NodeChildrenChanged && event.getPath().equals("/")) {
                    try {
                        showNodeList();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    } catch (KeeperException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        });

         showNodeList();
         Thread.sleep(Long.MAX_VALUE);
    }

    private static void showNodeList() throws InterruptedException, KeeperException {
        List<String> nodeList = zooKeeper.getChildren(path, true);
        System.out.println("====nodeList====");
        for (String node : nodeList) {
            System.out.println("nodeName:" + node);
        }
    }
}

　　

先运行程序，然后到客户端中增删znode，回来可见程序成功监控着“/”目录下znode的变化

 

DistributedClient.java

package com.hmb;

import org.apache.zookeeper.*;

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

public class DistributedClient {
    private String host = "localhost:2181";
    private CountDownLatch latch = new CountDownLatch(1);
    private String waitPath;
    private String thisPath;
    private ZooKeeper zk;
    private String groupNode = "group";
    private String subNode = "sub";

    public void connectZkServer() throws IOException, InterruptedException, KeeperException {
        zk = new ZooKeeper(host, 5000, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                if (event.getState() == Event.KeeperState.SyncConnected) {
                    latch.countDown();
                }

                if (event.getType() == Event.EventType.NodeDeleted && event.getPath().equals(waitPath)) {
                    try {
                        doSomething();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    } catch (KeeperException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        });

        latch.await();
        thisPath = zk.create("/" + groupNode + "/" + subNode, null, ZooDefs.Ids.OPEN_ACL_UNSAFE,
                CreateMode.EPHEMERAL_SEQUENTIAL);
        List<String> childrens = zk.getChildren("/" + groupNode, false);
        if (childrens.size() == 1) {
            doSomething();
        } else {
            String thisNode = thisPath.substring(("/" + groupNode + "/").length());
            Collections.sort(childrens);

            int idx = childrens.indexOf(thisNode);
            if (idx == 0) {
                doSomething();
            } else {
                waitPath = "/" + groupNode + "/" + childrens.get(idx - 1);
                zk.getData(waitPath, true, null);
            }
        }
    }

    private void doSomething() throws InterruptedException, KeeperException {
        System.out.println("get lock...");
        System.out.println(thisPath);
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        } finally {
            System.out.println("release lock...");
            zk.delete(thisPath, -1);
        }
    }

    public static void main(String[] args) throws InterruptedException {
        for (int i = 0; i < 10; i++) {
            new Thread() {
                @Override
                public void run() {
                    DistributedClient client = new DistributedClient();
                    try {
                        client.connectZkServer();
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    } catch (KeeperException e) {
                        throw new RuntimeException(e);
                    }
                }
            }.start();
        }
        Thread.sleep(Integer.MAX_VALUE);
    }
}

　　

到zk安装bin目录下，执行zkServer.cmd启动zk服务端，执行zkCli.cmd启动zk客户端，然后在客户端创建好group节点

 然后运行程序，结果如下