Class DefaultEventBus

  • All Implemented Interfaces:

    public class DefaultEventBus
    extends Object
    implements EventBus
    A default event bus implementation that synchronously publishes events to registered listeners. Listeners can be registered or unregistered for events as necessary.

    An event bus enables a publish/subscribe paradigm within Shiro - components can publish or consume events they find relevant without needing to be tightly coupled to other components. This affords great flexibility within Shiro by promoting loose coupling and high cohesion between components and a much safer pluggable architecture that is more resilient to change over time.

    Sending Events

    If a component wishes to publish events to other components:
         MyEvent myEvent = createMyEvent();
    The event bus will determine the type of event and then dispatch the event to components that wish to receive events of that type.

    Receiving Events

    A component can receive events of interest by doing the following.
    1. For each type of event you wish to consume, create a public method that accepts a single event argument. The method argument type indicates the type of event to receive.
    2. Annotate each of these public methods with the Subscribe annotation.
    3. Register the component with the event bus:
    After registering the component, when when an event of a respective type is published, the component's Subscribe-annotated method(s) will be invoked as expected. This design (and its constituent helper components) was largely influenced by Guava's EventBus concept, although no code was shared/imported (even though Guava is Apache 2.0 licensed and could have been used). This implementation is thread-safe and may be used concurrently.