@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1. Start Async
        final AsyncContext asyncContext = req.startAsync();
 
        // 2. Add Write Listener - to say Hello
        ServletOutputStream outputStream = resp.getOutputStream();
        WriteListener listener = new WriteListener() {
            @Override
            public void onWritePossible() throws IOException {
                // 3. Write to output stream 
                ServletOutputStream output = asyncContext.getResponse().getOutputStream();
                if (output.isReady()) {
                    output.print("Hello World!");
                }
 
                // 4. Call complete, to signal we are done
                asyncContext.complete();
            }
 
            @Override
            public void onError(Throwable throwable) {
                throwable.printStackTrace(System.err);
                asyncContext.complete();
            }
        };
        outputStream.setWriteListener(listener);
    }

    // EL을 사용할 수 있는 API를 제공하는 ELProcessor 생성
    ELProcessor processor = new ELProcessor();
 
    // 간단한 데이터 등록 및 EL 실행
    processor.defineBean("person", this.person);
    System.out.println(processor.eval("person.name"));
 
    // EL 3.0에서는 셋, 리스트, 맵을 쉽게 선언할 수 있다.
    Set set = (Set) processor.eval("{1, 2, 3, 3, 2, 1}");
    System.out.println("Set -> " + set);
 
    List list = (List) processor.eval("[1, 2, 3, 3, 2, 1]");
    System.out.println("List -> " + list);
 
    Map<String,Integer> map = (Map<String, Integer>) processor.eval("{'one': 1, 'two': 2, 'three': 3}");
    System.out.println("Map -> " + map);

@ServerEndpoint("/websockets/events/annotation")
public class EventsAnnotationEndpoint {
 
    // called when connection is opened, use blocking api to send a response message
    @OnOpen
    public void onOpen(Session session) {
        try {
            session.getBasicRemote().sendText("Welcome!");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    // called on close, we do nothing.
    @OnClose
    public void onClose() {
        // Clean up resources here
    }
 
    // called when a full message is received, we echo back to client using blocking api
    @OnMessage
    public void onMessage(Session session, String message) {
        try {
            session.getBasicRemote().sendText("Echo [" + message + "]");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
}