Java WebSocket API includes Endpoint and RemoteEndpoint artefacts. 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 of org.glassfish.tyrus.core.AnnotatedEndpoint which extends (and implements the abstract onOpen 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