ZooKeeper开发应用案例

public class ServiceRegister implements Runnable{
    private ZooKeeper zk;
    private static final String ZNODE = "/sas"; 
    private static final String SA_NODE_PREFIX = "sa_"; 
    private String hostName="localhost:2181"; 
    public void setHostName(String hostName) {
        this.hostName = hostName;
    }
     public ServiceRegister() throws IOException {
        zk = new ZooKeeper(hostName, 10000,null);
    }
  
    @Override
    public void run() {
        try {
             createSaNode();
            synchronized (this) {
                wait();
            }
 
        } catch (KeeperException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
 
    //测试用
    public static void main(String[] args){
        try {
            new ServiceRegister().run();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //创建子节点
    private String createSaNode() throws KeeperException, InterruptedException {
        // 如果根节点不存在，则创建根节点
        Stat stat = zk.exists(ZNODE, false);
        if (stat == null) {
            zk.create(ZNODE, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        }
 
        String hostName = System.getenv("HOSTNAME");
        // 创建EPHEMERAL_SEQUENTIAL类型节点
        String saPath = zk.create(ZNODE + "/" + SA_NODE_PREFIX,
                hostName.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,
                CreateMode.EPHEMERAL_SEQUENTIAL);
        return saPath;
    }
}

public class DataMonitor implements Watcher, AsyncCallback.ChildrenCallback { 
    ZooKeeper zk;
    String znode; 
    Watcher chainedWatcher; 
    boolean dead;
    DataMonitorListener listener;
     List<String> prevSaIds;
     public DataMonitor(ZooKeeper zk, String znode, Watcher chainedWatcher,
                       DataMonitorListener listener) {
        this.zk = zk;
        this.znode = znode;
        this.chainedWatcher = chainedWatcher;
        this.listener = listener;
        // 这是整个监控的真正开始，通过获取children节点开始。设置了本对象为监控对象，回调对象也是本对象。以后均是事件驱动。
        zk.getChildren(znode, true, this, null);
    }
 
    /**
     * 其他和monitor产生交互的类，需要实现此listener
     */
    public interface DataMonitorListener {
        /**
         * The existence status of the node has changed.
         */
        void changed(List<String> saIds);
 
        /**
         * The ZooKeeper session is no longer valid.
         *
         * @param rc
         *                the ZooKeeper reason code
         */
        void closing(int rc);
    }
 
   /*
    *监控/saids的回调函数。除了处理异常外。
    *如果发生变化，和构造函数中一样，通过getChildren，再次监控，并处理children节点变化后的业务
    */
    public void process(WatchedEvent event) {
        String path = event.getPath();
        if (event.getType() == Event.EventType.None) {
            // We are are being told that the state of the
            // connection has changed
            switch (event.getState()) {
                case SyncConnected:
                    // In this particular example we don't need to do anything
                    // here - watches are automatically re-registered with
                    // server and any watches triggered while the client was
                    // disconnected will be delivered (in order of course)
                    break;
                case Expired:
                    // It's all over
                    dead = true;
                    listener.closing(Code.SESSIONEXPIRED.intValue());
                    break;
            }
        } else {
            if (path != null && path.equals(znode)) {
                // Something has changed on the node, let's find out
                zk.getChildren(znode, true, this, null);
            }
        }
        if (chainedWatcher != null) {
            chainedWatcher.process(event);
        }
    }
 
    //拿到Children节点后的回调函数。
    @Override
    public void processResult(int rc, String path, Object ctx, List<String> children) {
        boolean exists;
        switch (rc) {
            case Code.Ok:
                exists = true;
                break;
            case Code.NoNode:
                exists = false;
                break;
            case Code.SessionExpired:
            case Code.NoAuth:
                dead = true;
                listener.closing(rc);
                return;
            default:
                // Retry errors
                zk.getChildren(znode, true, this, null);
                return;
        }
 
        List<String> saIds = null;
 
        //如果存在，再次查询到最新children，此时仅查询，不要设置监控了
        if (exists) {
            try {
                saIds = zk.getChildren(znode,null);
            } catch (KeeperException e) {
                // We don't need to worry about recovering now. The watch
                // callbacks will kick off any exception handling
                e.printStackTrace();
            } catch (InterruptedException e) {
                return;
            }
        }
 
        //拿到最新saids后，通过listener（executor），加载Saids。
        if ((saIds == null && saIds != prevSaIds)
                || (saIds != null && !saIds.equals(prevSaIds))) {
            listener.changed(saIds);
            prevSaIds = saIds;
        }
    }
}

public class LoadSaIdsExecutor
        implements Watcher, Runnable, DataMonitor.DataMonitorListener
{
 
    private DataMonitor dm;
    private ZooKeeper zk;
    private static final String znode = "/sas"; 
    private String hostName="localhost:2181";
    public void setHostName(String hostName) {
        this.hostName = hostName;
    }
 
        /*
         *初始化zookeeper及DataMonitor
         * 自己作为zookeeper的监控者，监控和zookeeper连接的变化
         * 自己作为DataMonitor的listener。当dm监控到变化时会调用executor执行业务操作
         */
    public LoadSaIdsExecutor() throws KeeperException, IOException {
        zk = new ZooKeeper(hostName, 300000, this);
        dm = new DataMonitor(zk, znode, null, this);
    }
 
    /**
     * 入口方法,测试用。
     */
    public static void main(String[] args) {
        try {
            new LoadSaIdsExecutor().run();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /**
     * 作为单独线程运行
     */
    public void run() {
        try {
            synchronized (this) {
                while (!dm.dead) {
                    wait();
                }
            }
        } catch (InterruptedException e) {
        }
    }
    /*
     *作为zookeeper监控者的回调，直接传递事件给monitor的回调函数统一处理
     */
    @Override
    public void process(WatchedEvent event) {
        dm.process(event);
    } 
    /*
     *当关闭时，让线程线继续走完
     */
    public void closing(int rc) {
        synchronized (this) {
            notifyAll();
        }
    }
 
    /*
     *监控到/saids变化后的处理类
     */
    static class SaIdsLoader extends Thread {
         List<String> saIds = null; 
        //构造对象后直接启动线程
        public SaIdsLoader(List<String> saIds){
            this.saIds = saIds;
            start();
        }
 
        public void run() {
            System.out.println("------------加载开始------------");
            //业务处理的地方
            if(saIds!=null){
                saIds.forEach(id->{
                    System.out.println(id);
                });
            }
            System.out.println("------------加载结束------------");
        }
    }
 
    /*
     *作为listener对外暴露的方法，在节点/saids变化时被调用。
     */
    @Override
    public void changed(List<String> data) {
                new SaIdsLoader(data);
    }
}