这一篇主要是介绍 zookeeper 开发环境的搭建以及客户端Java API的使用

1. zookeeper开发环境搭建

（1）首先要去官网下载安装包，下面给出传送门：
http://mirror.bit.edu.cn/apache/zookeeper/stable/

下载之后解压，这里我是解压在 /opt/目录下：

$tar -zxvf zookeeper-3.4.9.tar,gz

（2）解压之后就是要配置环境变量：
我是子啊Mac 下，所以是 ~/.bash_profile 文件中配置，如果是Linux下的话，应该是在~/.bashrc 下配置

export ZOOKEEPER_HOME=/opt/zookeeper-3.4.9
export PATH=$PATH:$ZOOKEEPER_HOME/bin

（3）配置了环境变量之后，就可以设置 zookeeper的配置文件了，默认是 zookeeper-3.4.9/conf/zoo.cfg 配置文件在zookeeper服务端在启动时被加载，但是conf目录下并没有这个文件，所以我们直接把conf目录下的 zoo_sample.cfg 复制成zoo.cfg 就OK，配置内容直接用默认的。

（4）启动服务端：运行一下命令：

$zkServer.sh start

这时服务端就启动了，通过以下命令可以查看服务端是否启动成功：

￥echo ruok | nc localhost 2181

具体执行过程可以看下图：
这里写图片描述

2. Java API的使用

对于zookeeper 的客户端连接， zookeeper 提供了一套 Java API来进行连接调用。

具体的详解这里就不给出了，直接给出具体的代码：

客户端连接回调的观察者ConnectionWatcher.java

package com.zookeeper.lyt;
import org.apache.zookeeper.*;
import java.util.concurrent.CountDownLatch;
/** * Created by louyuting on 2017/3/18. * 在 Zookeeper 中新建组 : /zoo */
public class ConnectionWatcher implements Watcher{ 
    private static final int SESSION_TIMEOUT = 5000;
    protected ZooKeeper zk;
    private CountDownLatch connectedSignal = new CountDownLatch(1);
    public void connect(String hosts) throws Exception{
        //传入: 主机地址; 会话超时参数; Watcher对象,用于接收来自zookeeper的回调,获得各种事件的通知.
        //内部会创建一个线程连接到服务器;
        zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
        //等待连接成功的响应.
        connectedSignal.await();
    }
    // override
    // 当客户端与服务端建立成功之后, watcher 的 process()方法会被调用. 参数是一个用于表示该连接的事件.
    public void process(WatchedEvent watchedEvent) {
        //返回响应, 表示连接已经成功
        if(watchedEvent.getState() == Event.KeeperState.SyncConnected){
            connectedSignal.countDown();
        }
    }
    /** * 创建一个新的 Zookeeper 的 znode, * @param groupName * @throws Exception */
    public void create(String groupName) throws Exception{
        String path = "/" + groupName;
        String createdPath = zk.create(path, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        System.out.println("created " + createdPath);
    }
    public void close() throws Exception{
        zk.close();
    }
}

创建组 CreateGroup.java

package com.zookeeper.lyt;
import org.apache.zookeeper.*;
import java.util.concurrent.CountDownLatch;
/** * Created by louyuting on 2017/3/18. * 在 Zookeeper 中新建组 : /zoo */
public class CreateGroup implements Watcher{ 
    private static final int SESSION_TIMEOUT = 5000;
    private ZooKeeper zk;
    private CountDownLatch connectedSignal = new CountDownLatch(1);
    public void connect(String hosts) throws Exception{
        //传入: 主机地址; 会话超时参数; Watcher对象,用于接收来自zookeeper的回调,获得各种事件的通知.
        //内部会创建一个线程连接到服务器;
        zk = new ZooKeeper(hosts, SESSION_TIMEOUT, this);
        //等待连接成功的响应.
        connectedSignal.await();
    }
    // override
    // 当客户端与服务端建立成功之后, watcher 的 process()方法会被调用. 参数是一个用于表示该连接的事件.
    public void process(WatchedEvent watchedEvent) {
        //返回响应, 表示连接已经成功
        if(watchedEvent.getState() == Event.KeeperState.SyncConnected){
            connectedSignal.countDown();
        }
    }
    /** * 创建一个新的 Zookeeper 的 znode, * @param groupName * @throws Exception */
    public void create(String groupName) throws Exception{
        String path = "/" + groupName;
        String createdPath = zk.create(path, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        System.out.println("created " + createdPath);
    }
    public void close() throws Exception{
        zk.close();
    }
    // main
    public static void main(String[] args) throws Exception {
        CreateGroup createGroup = new CreateGroup();
        createGroup.connect("ip:port");
        createGroup.create("zoo");
        createGroup.close();
    }
}

加入组 JoinGroup.java

package com.zookeeper.lyt;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.ZooDefs;
import java.util.concurrent.TimeUnit;
/** * Created by louyuting on 2017/3/18. * 加入组 */
public class JoinGroup extends ConnectionWatcher { 
    public void join(String groupName, String menberName) throws Exception{
        String path = "/" + groupName + "/" + menberName;
        String createdPath = zk.create(path, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        System.out.println("created " + createdPath);
    }
    public static void main(String[] args) throws Exception {
        JoinGroup joinGroup = new JoinGroup();
        joinGroup.connect("ip:port");
        joinGroup.join("zoo", "cow");
        TimeUnit.MICROSECONDS.sleep(Long.MAX_VALUE);
    }
}

列出组：ListGroup.java

package com.zookeeper.lyt;
import org.apache.zookeeper.KeeperException;
import java.util.List;
/** * Created by louyuting on 2017/3/18. * * 列出组成员 */
public class ListGroup extends ConnectionWatcher { 
    public void list(String groupName) throws Exception{
        String path = "/" + groupName;
        try {
            List<String> children= zk.getChildren(path, false);
            if(children.isEmpty()){
                System.out.println( path + " is empty");
                System.exit(1);
            }else {
                for (String child : children){
                    System.out.println(child);
                }
            }
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws Exception {
        ListGroup listGroup = new ListGroup();
        listGroup.connect("ip:port");
        listGroup.list("zoo");
        listGroup.close();
    }
}

删除组 DeleteGroup.java

package com.zookeeper.lyt;
import org.apache.zookeeper.KeeperException;
import java.util.List;
/** * Created by louyuting on 2017/3/18. * * 列出组成员 */
public class DeleteGroup extends ConnectionWatcher { 
    public void delete(String groupName) throws Exception{
        String path = "/" + groupName;
        try {
            List<String> children= zk.getChildren(path, false);
            for (String child : children){
                zk.delete(path + "/" + child, -1);
            }
            zk.delete(path, -1);
        } catch (KeeperException.NoNodeException e) {
            e.printStackTrace();
            System.out.println(groupName + " is not existed");
            System.exit(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws Exception {
        DeleteGroup deleteGroup = new DeleteGroup();
        deleteGroup.connect("ip:port");
        deleteGroup.delete("zoo");
        deleteGroup.close();
    }
}