Design Patterns and Best Practices in Java

Publisher-subscriber pattern

Commonly known as the Pub-Sub pattern, this can be thought of as an extension to event-driven communication. In event-driven communication, one action triggers an event, on the basis of which another component needs to perform some action. What if multiple components are interested in listening to a message? What if the same component is interested in listening to multiple types of message? The problem is solved by using the concept of topics. In broader terms, we can think of an event as a topic.

Let's revisit the example where an employee-record addition event needs to trigger an email to the manager. Let's say there are other components, such as a transportation system, salary management system, and so on, ...