nv-zookeeper

Overview

ZooKeeper Utility Library.

License

Apache License, Version 2.0

Maven

<dependency>
    <groupId>com.neovisionaries</groupId>
    <artifactId>nv-zookeeper</artifactId>
    <version>1.2</version>
</dependency>

Source Download

git clone http://github.com/TakahikoKawasaki/nv-zookeeper.git

JavaDoc

JavaDoc of nv-zookeeper

Examples

Leader Election

// Prepare a ZooKeeper instance.
ZooKeeper zooKeeper = ...

// Prepare a Listener implementation.
LeaderElection.Listener listener = new LeaderElection.Leader() {
    @Override
    public void onWin(LeaderElection election) {
        System.out.println("I'm the leader.");
    }

    @Override
    public void onLose(LeaderElection election) {
        System.out.println("Someone else is the leader.");
    }

    @Override
    public void onVacant(LeaderElection election) {
        System.out.println("The leader resigned. An election will be conducted again.");
    }

    @Override
    public void onFinish(LeaderElection election) {
        System.out.println("The callback chain ended. Not run for election any more.");
    }

    @Override
    public void onStateChanged(LeaderElection election, State oldState, State newState) {
        System.out.format("The state was changed from %s to %s.\n", oldState, newState);
    }
};

// Conduct a leader election.
new LeaderElection()
    .setZooKeeper(zooKeeper)
    .setListener(listener)
    .start();

// Same as above.
new LeaderElection()
    .setZooKeeper(zooKeeper)
    .setListener(listener)
    .setPath("/leader")
    .setId(
        String.valueOf(Math.abs(new Random().nextLong()))
    )
    .setAclList(ZooDefs.Ids.OPEN_ACL_UNSAFE)
    .start();

This implementation repeats to join a leader election, i.e. continues to schedule a callback (and a watcher as necessary), until it detects either of the following.

The given ZooKeeper instance reports AUTH_FAILED or CLOSED.
This instance is marked as shouldStop by finish().

LeaderElection.Adapter is an empty implementation of LeaderElection.Listener. You may find it useful when you are interested in only some of the callback methods. For example, if you are interested in only onStateChanged(), using Adapter will make your code shorter like below.

// Conduct a leader election.
new LeaderElection()
    .setZooKeeper(zooKeeper)
    .setListener(new Adapter() {
        @Override
        public void onStateChanged(LeaderElection election, State oldState, State newState) {
            System.out.format("The state was changed from %s to %s.\n", oldState, newState);
        }
    })
    .start();

Author

Takahiko Kawasaki, Neo Visionaries Inc.

TakahikoKawasaki/nv-zookeeper