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

## Annotated Endpoints

The following example shows how to create the same endpoint from Programmatic Endpoints using annotations instead:

    @ServerEndpoint("/echo")
    public class EchoEndpoint {
       @OnMessage
       public void onMessage(Session session, String msg) {
          try {
             session.getBasicRemote().sendText(msg);
          } catch (IOException e) { ... }
       }
    }

The annotated endpoint is simpler than the equivalent programmatic endpoint, and it is deployed automatically with the application to the relative path defined in the `ServerEndpoint` annotation. Instead of having to create an additional class for the message handler, this example uses the `OnMessage` annotation to designate the method invoked to handle messages.

Table 19-1 lists the annotations available in the `javax.websocket` package to designate the methods that handle lifecycle events. The examples in the table show the most common parameters for these methods. See the API reference for details on what combinations of parameters are allowed in each case.

Table 19-1 WebSocket Endpoint Lifecycle Annotations

Annotation | Event | Example
`OnOpen` | Connection opened |
    @OnOpen
    public void open(Session session,
                     EndpointConfig conf) { }
`OnMessage` | Message received |
    @OnMessage
    public void message(Session session,
                        String msg) { }
`OnError` | Connection error |
    @OnError
    public void error(Session session,
                      Throwable error) { }
`OnClose` | Connection closed |
    @OnClose
    public void close(Session session,
                      CloseReason reason) { }

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