37. Zookeeper Support

37.1 Introduction

Zookeeper support was added to the framework in version 4.2, comprised of:

  • MetadataStore
  • LockRegistry
  • Leadership Event Handling

37.2 Zookeeper Metadata Store

The ZookeeperMetadataStore can be used where any MetadataStore is needed, such as peristent file list filters, etc. See Section 9.5, “Metadata Store” for more information.

<bean id="client" class="org.springframework.integration.zookeeper.config.CuratorFrameworkFactoryBean">
    <constructor-arg value="${connect.string}" />

<bean id="meta" class="org.springframework.integration.zookeeper.metadata.ZookeeperMetadataStore">
    <constructor-arg ref="client" />
public MetadataStore zkStore(CuratorFramework client) {
    return new ZookeeperMetadataStore(client);

37.3 Zookeeper Lock Registry

The ZookeeperLockRegistry can be used where any LockRegistry is needed, such as when using an Aggregator in a clustered environment, with a shared MessageStore.

A LocRegistry is used to "look up" a lock based on a key (the aggregator uses the correlationId). By default, locks in the ZookeeperLockRegistry are maintained in zookeeper under the path /SpringIntegration-LockRegistry/. You can customize the path by providing an implementation of ZookeeperLockRegistry.KeyToPathStrategy.

public interface KeyToPathStrategy {

    String pathFor(String key);

    boolean bounded();


If the strategy returns true from isBounded, unused locks do not need to be harvested. For unbounded strategies (such as the default) you will need to invoke expireUnusedOlderThan(long age) from time to time, to remove old unused locks from memory.

37.4 Zookeeper Leadership Event Handling

Groups of endpoints can be started/stopped based on leadership being granted or revoked respectively. This is useful in clustered scenarios where shared resources must only be consumed by a single instance. An example of this is a file inbound channel adapter that is polling a shared directory. (See Section 14.2, “Reading Files”).

<int-zk:leader-listener client="client" path="/siNamespace" role="cluster" />

client is a reference to a CuratorFramework bean; a CuratorFrameworkFactoryBean is available. When a leader is elected, an OnGrantedEvent will be published for the role cluster; any endpoints in that role will be started. When leadership is revoked, an OnRevokedEvent will be published for the role cluster; any endpoints in that role will be stopped. See Section 8.2, “Endpoint Roles” for more information.

public LeaderInitiatorFactoryBean leaderInitiator(CuratorFramework client) {
    return new LeaderInitiatorFactoryBean(client, "/siTest/", "cluster");