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Zookeeper: Example

Sumit Rawal answered on June 1, 2023 Popularity 3/10 Helpfulness 1/10

answer Zookeeper: Example

Zookeeper: Example

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So what kind of problems can Zookeeper solve? Zookeeper’s higher-level constructs can solve several common distributed systems problems. A list of such recipes appears on the official project website. We’ll work with a simple problem to demonstrate the use of the Zookeeper API. We’ll write a program that has a spawned thread, create a znode, and update it with a new value after every second for a total of five times. A watch is set on the same znode in the main thread. Notifications are received whenever the znode value changes. The values are printed on the console. The code for the program appears below:

public class ZookeeperExample implements Watcher {

    final String zNodePath = "/MyZNode";
    ZooKeeper zk;

    public static void main(String[] args) throws Exception {

        // Set-up Zookeeper instance
        ZookeeperExample zkExample = new ZookeeperExample();
        zkExample.zk = new ZooKeeper("localhost:2181", 3000, zkExample);

        // Set a watch on the znode. Note, the Znode hasn't been created as yet
        zkExample.zk.addWatch(zkExample.zNodePath, AddWatchMode.PERSISTENT);

        // Create a thread to modify the znode
        Thread mThread = new Thread(() -> {
            zkExample.modifier();
        });

        // Wait for thread to finish
        mThread.start();
        mThread.join();

        // Close connection
        zkExample.zk.close();

        System.out.println("\nAll Done.");
    }


    /**
     * Method executed by the spawned thread
     */
    public void modifier() {

        try {
            // Create a znode
            zk.create(zNodePath, "Hello".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);

            for (int i = 0; i < 5; i++) {
                // sleep for a second and change the znode value
                Thread.sleep(1000);
                zk.setData(zNodePath, ("Hello " + (i + 1)).getBytes(), -1);
            }

            // Delete the znode
            zk.delete(zNodePath, -1);
        } catch (Exception ie) {
            // swallow, but don't do this in production
        }
    }

    /**
     * Callback method that receives notifications for the set watch
     *
     * @param event
     */
    public void process(WatchedEvent event) {
        System.out.println(String.format("\nNotification received of change for znode %s %s",
                event.getPath(),
                event.getType()));
        Stat stat = new Stat();
        try {
            byte[] data = zk.getData(zNodePath, false, stat);
            String updatedVal = new String(data, StandardCharsets.UTF_8);
            System.out.println("Updated znode values " + updatedVal);

        } catch (Exception e) {
            // swallow, but don't do this in production
        }
    }
}

Popularity 3/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: java

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Contributed on Jun 01 2023

Sumit Rawal

0 Answers Avg Quality 2/10

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