If you encounter the Endpoint and RemoteEndpoint artefacts from the Java WebSocket API for the first time, you might think they represent the same concept or you might even guess that they are hierarchical in nature. It is not the case.

Endpoint: The Class

javax.websocket.Endpoint is a simple (abstract) class which represents a WebSocket endpoint itself – either a server or a client endpoint. The Java WebSocket API itself provides both annotation and programmatic APIs to develop and design endpoints. An annotation based endpoint can be developed with the help of the following annotations

• @ServerEndpoint or @ClientEndpoint
• @OnMessage
• @OnClose
• @OnMessage and
• @OnError

When you deploy an annotated WebSocket endpoint using Tyrus (WebSocket Reference Implementation), it internally creates an instance oforg.glassfish.tyrus.core.AnnotatedEndpoint which extends (and implements the abstractonOpen method)

In case you want to use the programmatic API, you would need to extend the Endpoint class and override the (abstract) onOpen method yourself.

RemoteEndpoint: The Interface

WebSocket is just a protocol using which two parties (client and server) communicate.javax.websocket.RemoteEndpoint is an abstraction which represents the entity at the other end. It is available is two avatars

• Synchronous: RemoteEndpoint.Basic
• Asynchronous: RemoteEndpoint.Async

A RemoteEndpoint instance is encapsulated within the javax.websocket.Session object and can be obtained using the getBasicRemote or getAsyncRemote methods (for sync and async operation respectively). Here is the Tyrus implementation – org.glassfish.tyrus.core. TyrusRemoteEndpoint

Cheers!