2、zookeeper 系列 -- 简单学习 zk 提供的 java API

前置声明

maven

<dependencies>
    <dependency>
        <groupId>org.apache.zookeeper</groupId>
        <artifactId>zookeeper</artifactId>
        <version>3.5.5</version>
    </dependency>
</dependencies>

创建会话

public class MyZookeeper implements Watcher {

    private static CountDownLatch latch = new CountDownLatch(1);

    public static void main(String[] args) {
        try {
            ZooKeeper zooKeeper = new ZooKeeper("192.168.1.102:2181", 5000, new MyZookeeper());
            System.out.println(zooKeeper.getState());
            try {
                latch.await();
            } catch (InterruptedException e) {
            }
            System.out.println("zookeeper session established");
        } catch (IOException e) {
        }
    }


    @Override
    public void process(WatchedEvent event) {
        System.out.println("Receive watched event：" + event);
        if (KeeperState.SyncConnected == event.getState()) {
            latch.countDown();
        }
    }
}

创建节点

public String create(final String path, byte data[], List<ACL> acl, CreateMode createMode)

zooKeeper.create("/zk-1", "hello".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

删除节点

public void delete(final String path, int version) throws InterruptedException, KeeperException

zooKeeper.delete("/zk-book", -1);

描述：

• version： 这里的version，表示的是dataVersion。-1，表示匹配任何一个版本。

public void delete(final String path, int version, VoidCallback cb, Object ctx)

zooKeeper.delete("/zk-book", -1, (int rc, String path, Object context) -> {
            System.out.printf("rc = %d\npath = %s\ncontext = %s\n", rc, path, path, context.toString());
        }, "I am context data");
Thread.sleep(3000);

描述：

• 异步删除
• Object ctx： 上下文数据，可传递到回调函数
• VoidCallback cb： 回调函数

获取节点

public List<String> getChildren(final String path, Watcher watcher) throws KeeperException, InterruptedException

List<String> children = zooKeeper.getChildren("/zk-book", new MyZookeeper());
children.forEach(System.out::println);

描述：

• 获取该节点下的直接子节点，无法递归获取（zk client 的 ls -R /zk-book 可递归获取）

public void getChildren(final String path, Watcher watcher, Children2Callback cb, Object ctx)

zooKeeper.getChildren("/zk-book", new MyZookeeper(), (int rc, String path, Object ctx, List<String> children, Stat stat) -> System.out.printf("rc = %d\tpath = %s\tctx = %s\tchidren = %s\tstat = %s\n", rc, path, ctx, String.join(",", children),stat.toString()), "I am callback data");
zooKeeper.create("/zk-book/zb3", "hello".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
Thread.sleep(3000);

描述：

• 异步获取数据
• 当注册监听的时候，/zk-book 下的节点若改变，则会触发 NodeChildrenChanged 事件。

读取数据

public byte[] getData(final String path, Watcher watcher, Stat stat)throws KeeperException, InterruptedException

byte[] data = zooKeeper.getData("/zk-book", new MyZookeeper(), null);
System.out.println(new String(data, 0, data.length));

public void getData(final String path, Watcher watcher, DataCallback cb, Object ctx)

zooKeeper.getData("/zk-book", new MyZookeeper(), (int rc, String path, Object ctx, byte data[], Stat stat) -> {}, null);
Thread.sleep(3000);

描述

• 异步获取数据

更新数据

public Stat setData(final String path, byte data[], int version) throws KeeperException, InterruptedException

Stat stat1 = zooKeeper.setData("/zk-book", "hello".getBytes(), -1);

public void setData(final String path, byte data[], int version, StatCallback cb, Object ctx)

zooKeeper.setData("/zk-book", "hello".getBytes(), -1, (int rc, String path, Object ctx, Stat stat) ->{},  null);
Thread.sleep(3000);

描述

• 异步更新数据

检查是否存在

public Stat exists(final String path, Watcher watcher) throws KeeperException, InterruptedException

Stat exists = zooKeeper.exists("/zk-book", new MyZookeeper());

描述

• Watcher watcher 监听 3 类事件。

  • 节点被创建
  • 节点被删除
  • 节点被更新

public void exists(final String path, Watcher watcher, StatCallback cb, Object ctx)

zooKeeper.exists("/zk-book", new MyZookeeper(), (int rc, String path, Object ctx, Stat stat) -> {}, null);

描述

• 异步判断是否存在