Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## 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`.

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