Zookeeper学习笔记（三）——java客户端代码操作

Zookeeper客户端java代码操作

上篇博客记录了shell命令操作zookeeper集群的方式，这次尝试采用java代码来操作。通过查阅API，发现并不困难。

1. 首先获得客户端与服务器的连接

    //zookeeper客户端
    private ZooKeeper zkCli;
    //连接地址
    private static final String CONNECT_STRING = "hadoop102:2181,hadoop103:2181,hadoop104:2181";
    //session过期时间
    private static final int SESSION_TIMEOUT = 2000;

    /**
     * 创建客户端实例对象
     *
     * @throws IOException
     */
    @Before
    public void before() throws IOException {
        zkCli = new ZooKeeper(CONNECT_STRING, SESSION_TIMEOUT, (event) -> {
            System.out.println("默认的回调函数");
        });
    }

2. 列出根节点下的子节点(非递归)

    @Test
    public void ls() throws KeeperException, InterruptedException {
        List<String> children = zkCli.getChildren("/", e -> {
            System.out.println("自定义回调函数");
        });

        System.out.println("---------------------");
        for (String child : children) {
            System.out.println(child);
        }
        System.out.println("+++++++++++++++++++++");

        Thread.sleep(Long.MAX_VALUE);

    }

3. 在一个节点下创建子节点

    @Test
    public void create() throws KeeperException, InterruptedException {

        //parameter1：创建的节点路径  parameter2：节点的数据 parameter3：节点权限  parameter4：节点类型
        String str = zkCli.create("/idea", "idea2019".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        System.out.println(str);
        Thread.sleep(Long.MAX_VALUE);
    }

4. 获取指定节点的内容

    @Test
    public void get() throws KeeperException, InterruptedException {
        byte[] data = zkCli.getData("/simon", true, new Stat());
        String str = new String(data);
        System.out.println(str);
    }

5. 给指定节点设置值

    @Test
    public void set() throws KeeperException, InterruptedException {
        Stat stat = zkCli.setData("/simon", "abcd".getBytes(), 1);
        System.out.println(stat.getDataLength());
    }

6. 获取指定节点的状态信息

    @Test
    public void stat() throws KeeperException, InterruptedException {

        Stat exists = zkCli.exists("/ideaa", false);
        if (exists == null) {
            System.out.println("节点不存在");
        } else {
            System.out.println(exists.getDataLength());
        }
    }

7. 删除指定节点

    @Test
    public void delete() throws KeeperException, InterruptedException {
        Stat exists = zkCli.exists("/idea", false);
        if (exists != null) {
            zkCli.delete("/idea", exists.getVersion());
        }
    }

8. 循环注册，动态获取节点的信息。

也就是当节点有任何变化时，就会调用回调函数，动态的显示节点的变化信息。

    @Test
    public void register() throws KeeperException, InterruptedException {
        byte[] data = zkCli.getData("/simon2", new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                try {
                    register();//发生事件，通知的时候在注册一遍，实现了循环调用
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, null);
        System.out.println(new String(data));
    }


    @Test
    public void testRegister() {
        try {
            register(); //调用register()方法,将进程卡住，循环执行register
            Thread.sleep(Long.MAX_VALUE);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

代码很简单易懂，只是有些内部原理还是有些模糊，例如：Stat是什么？zookeeper是怎么监听到节点发生变化的？又是如何将变化通知给客户端的？在之后的博客中将会详细记录。~