@OnMessage public String getHeaders(Session session, String headerKey) { StringBuilder response = new StringBuilder(); response.append("Request Header [").append(headerKey).append("]: "); @SuppressWarnings("unchecked") Map<String, List<String>> headers = (Map<String, List<String>>) session.getUserProperties().get("request-headers"); if (headers == null) { response.append("<no headers found in session.getUserProperties()>"); } else { List<String> values = headers.get(headerKey); if (values == null) { response.append("<header not found>"); } else { response.append(QuoteUtil.join(values, ",")); } } return response.toString(); }