Comment by RedShift1
11 hours ago
I'm a big fan of Guava's EventBus. Easy to implement and straightforward to understand. This library does seem to require more setup and I don't see the immediate advantages, also why does it require an instanceProvider? I don't understand what that does.
Emissary really shines if performance is a top priority.
The setup is more or less similar, you register a bunch of event handlers when initializing the library. The main difference is that, in addition to events, Emissary also supports "request" messages. Requests enforce the invariant that only one handler should handle it - if there are multiple handlers registered for a given request, Emissary will throw an error. That, and some extension points which is only needed for more advance use cases.
The InstanceProvider allows users to let the dependency injection (DI) framework of their choice instantiate the request/event handler classes (see https://github.com/joel-jeremy/emissary?tab=readme-ov-file#e...). This is in contrast to the way EventBus does it where subscribers need to be instantiated at startup time. By leveraging the DI framework, additional services can be injected to the handler's constructor.