18.3 Programmatic Endpoints

The following example shows how to create an endpoint by extending the Endpoint class:

public class EchoEndpoint extends Endpoint {
   @Override
   public void onOpen(final Session session, EndpointConfig config) {
      session.addMessageHandler(new MessageHandler.Whole<String>() {
         @Override
         public void onMessage(String msg) {
            try {
               session.getBasicRemote().sendText(msg);
            } catch (IOException e) { ... }
         }
      });
   }
}

This endpoint echoes every message received. The Endpoint class defines three lifecycle methods: onOpen, onClose, and onError. The EchoEndpoint class implements the onOpen method, which is the only abstract method in the Endpoint class.

The Session parameter represents a conversation between this endpoint and the remote endpoint. The addMessageHandler method registers message handlers, and the getBasicRemote method returns an object that represents the remote endpoint. The Session interface is covered in detail in the rest of this chapter.

The message handler is implemented as an anonymous inner class. The onMessage method of the message handler is invoked when the endpoint receives a text message.

To deploy this programmatic endpoint, use the following code in your Java EE application:

ServerEndpointConfig.Builder.create(EchoEndpoint.class, "/echo").build();

When you deploy your application, the endpoint is available at ws://<host>:<port>/<application>/echo; for example, ws://localhost:8080/echoapp/echo.