使用JAVA API调用ZooKeeper

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#java #zookeeper #大数据

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一、环境准备及创建会话实例

JAR包

使用JAVA API调用ZooKeeper时必须要导入对应的jar包

对应的jar包:ZooKeeper-3.x.x.jar（其中的x需要依据版本而定。注意：使用3.4.14版本的ZooKeeper时，如何使用3.4.14的jar包，创建连接时需要把session超时时间设置长一点否则会报错，改用3.4.10版本的jar包则无此问题）

在lib目录下的jar包也是需要导入的

2. 创建会话实例

需要访问ZooKeeper的第一步是需要先保证可以创建会话实例

创建会话实例的方法

ZooKeeper(String connectString,int sessionTimeout,Watcher watcher)

connectString：表示连接到哪一个Zookeeper，如192.168.2.2:2181

sessionTimeout：表示会话过期时间，单位是毫秒

watcher：通过注册Watcher来实现对节点的状态变化监听

关于ZooKeeper的构造方法还有如下几个：

ZooKeeper(String connectString,int sessionTimeout,Watcher watcher,boolean canBeReadOnly)

ZooKeeper(String connectString,int sessionTimeout,Watcher watcher,long sessionId,boolean canBeReadOnly)

ZooKeeper(String connectString,int sessionTimeout,Watcher watcher,long sessionId,byte[] sessionPasswd,boolean canBeReadOnly)

canBeReadOnly：表示当前会话是否支持read-only

sessionId：表示会话的ID

sessionPasswd：密钥

关于watcher

watcher是org.apache.Zookeeper.Watcher类型的对象，当客户端和服务器建立连接后会调用Watcher中的process方法，这个方法中会有一个WatchedEvent类型的参数，它用来标识发生了哪一种事件

WatchedEvent主要包含以下两个方面的信息：

watchedEvent.getState()：取得与服务器连接状态，这里的连接状态包含（SyncConnected、Disconnected、connectedReadOnly、AuthFailed等）

watchedEvent.getType()：取得节点事件类型，通过它可以获得具体的事件类型，这里事件类型的取值包含（None、NodeCreated、NodeDeleted、 NodeDataChanged、NodeChildrenChanged）

注意：Watcher通知是一次性的，当一旦触发一次通知后，这个Watcher就无效了，客户端需要再次注册Watcher,否则无法再次监听到节点的状态变化

二、使用JAVA API调用ZooKeeper

使用JAVA API创建节点

public class ZooKeeperDemo implements Watcher{
    private static final int SESSION_TIMEOUT = 3000;
    public static ZooKeeper ZooKeeper;
    public static void main(String[] args) {
        String path = "/mynode";
        try {
            ZooKeeper = new ZooKeeper("192.168.2.2:2181",SESSION_TIMEOUT,new ZooKeeperDemo());
            ZooKeeper.exists(path,true);
            ZooKeeper.create(path,"mycontent 1".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            Thread.sleep(3000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }




    @Override
    public void process(WatchedEvent event) {
        if(Event.KeeperState.SyncConnected == event.getState()){
            if(Event.EventType.NodeCreated == event.getType()){
                //创建成功时在此处进行回调
                System.out.println("node创建成功！");
                try {
                    ZooKeeper.exists(event.getPath(),true);
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

创建节点语句：

ZooKeeper.create(path,"mycontent 1".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

第一个参数：path，是一个局部变量“/mynode”

第二个参数："mycontent 1".getBytes(),指的是创建节点的数据值

第三个参数： ZooDefs.Ids. OPEN_ACL_UNSAFE ,指的是这个节点的访问权限为任何人可以访问

第四个参数：CreateMode.PERSISTENT，指的是创建节点的类型，这里指的是在会话重启后节点仍然存在

节点的创建、取值、修改、删除操作

public class ZookeeperDemo01 implements Watcher {
    //定义sessioTimeout常量
    private static final int SESSION_TIMEOUT = 30000;
    public static ZooKeeper zooKeeper;


    public static void main(String[] args) {
        createNode("/zknode1");
        getContent("/zknode1");
        setContent("/zknode1","你好!");
        getContent("/zknode1");
        deleteNode("/zknode1");
        closeConnect(zooKeeper);
    }




    @Override
    public void process(WatchedEvent watchedEvent) {
        if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
            if (Event.EventType.NodeCreated == watchedEvent.getType()) {
                //创建节点的消息通知
                System.out.println("创建节点成功! 时间：" + new SimpleDateFormat("yyyy-mm-dd HH:mm:ss").format(new Date()));
                try {
                    zooKeeper.exists(watchedEvent.getPath(), true);
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            } else if(Event.EventType.NodeDeleted == watchedEvent.getType()){
                try {
                    zooKeeper.exists(watchedEvent.getPath(),true);
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("节点被删除! 时间：" + new SimpleDateFormat("yyyy-mm-dd HH:mm:ss").format(new Date()));
            } else if(Event.EventType.NodeDataChanged == watchedEvent.getType()){
                try {
                    zooKeeper.exists(watchedEvent.getPath(),true);
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("节点被修改! 时间：" + new SimpleDateFormat("yyyy-mm-dd HH:mm:ss").format(new Date()));
            }
        }
    }


    /**
     * 创建节点
     *
     * @param path
     */
    public static void createNode(String path) {
        try {
            zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
            zooKeeper.exists(path, true);
            //创建节点
            zooKeeper.create(path, "xiesheng".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            Thread.sleep(3000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    /**
     * 获取节点的内容
     *
     * @param path
     * @return
     */
    public static String getContent(String path) {
        try {
            if (zooKeeper == null) {
                zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
            }
            byte[] rb = zooKeeper.getData(path, null, null);
            System.out.println("获取节点【" + path + "】的内容为：" + new String(rb));
            Thread.sleep(3000);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }


    /**
     * 设置节点的内容
     * @param path
     * @param content
     */
    public static void setContent(String path,String content) {
        try {
            if (zooKeeper == null) {
                zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
            }
            zooKeeper.setData(path, content.getBytes(), -1);
            Thread.sleep(3000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    /**
     * 删除节点
     * @param path
     */
    public static void deleteNode(String path){
        try {
            if (zooKeeper == null) {
                zooKeeper = new ZooKeeper("192.168.2.4:2181", SESSION_TIMEOUT, new ZookeeperDemo01());
            }
            zooKeeper.delete(path,-1);
            Thread.sleep(3000);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    /**
     * 关闭连接
     * @param zooKeeper
     */
    public static void closeConnect(ZooKeeper zooKeeper){
        if(zooKeeper == null){
            System.out.println("未连接，无需关闭！");
        } else {
            try {
                zooKeeper.close();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("连接关闭成功！");
        }
    }
}

进行以上测试后控制台打印结果如下：

创建节点成功! 时间：2020-13-04 11:13:11

获取节点【/zknode1】的内容为：xiesheng

节点被修改! 时间：2020-13-04 11:13:17

获取节点【/zknode1】的内容为：你好!

节点被删除! 时间：2020-13-04 11:13:23

连接关闭成功！