Event Notification Pattern with Spring Data

In This article, we will implement a simple Event Notification Pattern using Spring Data.

When an entity is updated, removed, or persisted, an event is published to notify other systems of the change.

We will also enhance the notification process by incorporating DTO objects, eliminating the need to fetch updated data. This enhancement addresses one of the downsides of the Event Notification Pattern compared to Event Sourcing.

The full application code is available on GitHub.

Photo by Max LaRochelle on Unspash

1- Entity Listeners

To start, we use @EntityListeners to specify the listener class for an entity. Below is an example where the Book entity is annotated to listen to lifecycle events via the BookEntityListener class:

@Entity
@Table(name = "books")
@EntityListeners(BookEntityListener.class)
public class Book extends AbstractEntity {
   
   // fields
   
}

The listener class itself is a Spring bean, annotated with @Component. It can handle events for multiple entities and publish corresponding events using a uniform object structure.

@Component
@RequiredArgsConstructor
public class BookEntityListener {
    private final ApplicationEventQueue…