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Listening to Events

You can register for Hazelcast entry events so you are notified when those events occur. Event listeners are cluster-wide: when a listener is registered in one member of cluster, it is actually registered for the events that originated at any member in the cluster. When a new member joins, events originated at the new member are also delivered.

An event is created only if you registered an event listener. If no listener is registered, then no event is created. If you provided a predicate when you registered the event listener, pass the predicate before sending the event to the listener (member/client).

As a rule of thumb, your event listener should not implement heavy processes in its event methods that block the thread for a long time. If needed, you can use ExecutorService to transfer long running processes to another thread and thus offload the current listener thread.

In a failover scenario, events are not highly available and may get lost. However, you can perform workarounds such as configuring the event queue capacity as explained in the Global Event Configuration section.

Hazelcast offers the following event listeners.

For cluster events:

  • Membership Listener for cluster membership events

  • Distributed Object Listener for distributed object creation and destruction events

  • Migration Listener for partition migration start and completion events

  • Partition Lost Listener for partition lost events

  • Lifecycle Listener for HazelcastInstance lifecycle events

  • Client Listener for client connection events

For distributed object events:

  • Entry Listener for IMap and MultiMap entry events

  • Item Listener for IQueue, ISet and IList item events

  • Message Listener for ITopic message events

For Hazelcast JCache implementation:

For Hazelcast clients:

  • Lifecycle Listener

  • Membership Listener

  • Distributed Object Listener