User Defined Services

In the case of special/custom needs, Hazelcast's SPI (Service Provider Interface) module allows users to develop their own distributed data structures and services.

A Counter User Defined Service

Throughout this section, we create a distributed counter that will be the guide to reveal the Hazelcast SPI usage.

Here is our counter.

public interface Counter{
   int inc(int amount);
}

This counter will have the following features:

• It will be stored in Hazelcast.
• Different cluster members can call it.
• It will be scalable, meaning that the capacity for the number of counters scales with the number of cluster members.
• It will be highly available, meaning that if a member hosting this counter goes down, a backup will be available on a different member.

All these features are done with the steps below. Each step adds a new functionality to this counter.

1. Create the class.
2. Enable the class.
3. Add properties.
4. Place a remote call.
5. Create the containers.
6. Enable partition migration.
7. Create the backups.