scala-zookeeper-client

About

A Scala client for Apache ZooKeeper, "a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services".

ZooKeeper provides a Java client library that's perfectly usable from Scala. This just wraps some idioms and niceties around that library to make it as Scala-friendly as possible. It also ships with tests, so you can have some confidence that you'll be able to interact with ZooKeeper from Scala in a predictable and reliable way.

The scala-zookeeper-client will automatically handle session expired events by creating a new connection to the Zookeeper servers. We also provide several commonly used operations and utilities on top of Zookeeper's minimal API:

Create a path of nodes, similar to 'mkdir -p'
Recursively delete a tree of nodes
Watch a node forever
Monitor a node's child set
For a given node, maintain a map from the node's children to the each child's data

Usage

Basic usage:

import com.twitter.zookeeper.ZooKeeperClient

val zk = new ZooKeeperClient("localhost:2181")

zk.createPath("/a/b/c")
zk.createPath("/a/b/d")
val children = zk.getChildren("/a/b") // Seq("c", "d")

zk.set("/a/b/c", "foo".getBytes())
val s = new String(zk.get("/a/b/c")) // "foo"

zk.deleteRecursive("/a") // delete "a" and all children

Advanced features:

Monitor a node forever:

import com.twitter.zookeeper.ZooKeeperClient
import org.apache.zookeeper.CreateMode

val zk = new ZooKeeperClient("localhost:2181")
zk.create("/test-node", "foo".getBytes, CreateMode.PERSISTENT)
zk.watchNode("/test-node", { (data : Option[Array[Byte]]) =>
  data match {
    case Some(d) => println("Data updated: %s".format(new String(d)))
case None => println("Node deleted")
  }
})
zk.set("/test-node", "bar".getBytes)
zk.set("/test-node", "baz".getBytes)
zk.delete("/test-node")

Monitor a node's children:

import com.twitter.zookeeper.ZooKeeperClient
import org.apache.zookeeper.CreateMode

val zk = new ZooKeeperClient("localhost:2181")
zk.create("/parent", null, CreateMode.PERSISTENT)
zk.watchChildren("/parent", { (children : Seq[String]) =>
  println("Children: %s".format(children.mkString(", ")))
})
zk.create("/parent/child1", null, CreateMode.PERSISTENT)
zk.create("/parent/child2", null, CreateMode.PERSISTENT)
zk.delete("/parent/child1")
zk.create("/parent/child3", null, CreateMode.PERSISTENT)
zk.deleteRecursive("/parent")

For a given node, automatically maintain a map from the node's children to the each child's data:

import com.twitter.zookeeper.ZooKeeperClient
import org.apache.zookeeper.CreateMode
import scala.collection.mutable

val zk = new ZooKeeperClient("localhost:2181")
val childMap = mutable.Map[String, String]()

zk.create("/parent", null, CreateMode.PERSISTENT)
zk.watchChildrenWithData("/parent", childMap, {data => new String(data)})

zk.create("/parent/a", "foo".getBytes, CreateMode.PERSISTENT)
zk.create("/parent/b", "bar".getBytes, CreateMode.PERSISTENT)
println("child map: %s".format(childMap)) // NOTE: real code should synchronize access on childMap

zk.delete("/parent/a")
zk.set("/parent/b", "bar2".getBytes)
zk.create("/parent/c", "baz".getBytes, CreateMode.PERSISTENT)
println("child map: %s".format(childMap)) // NOTE: real code should synchronize access on childMap

Get the internal zookeeper handle to pass to other libraries:

import com.twitter.zookeeper.ZooKeeperClient
import org.apache.zookeeper.ZooKeeper

def zkListener(zkHandle : ZooKeeper) {
  // use zkHandle
  println("Internal zookeeper handle changed: %s".format(zkHandle))
  // Note that zkListener will be called with a new handle whenever the Zookeeper session
  // has expired and a new connection to the Zookeeper servers is created
}

val zk = new ZooKeeperClient("localhost:2181", zkListener _)

Authors

License

Apache License, Version 2.0. See the LICENSE file for more information.