servlet.clj

(defn ^ServerContainer server-container [^ServletContext context]
  (.getAttribute context "javax.websocket.server.ServerContainer"))

(defn add-endpoint
  "Adds an endpoint to a container obtained from the servlet-context"
  [^ServletContext servlet-context {:keys [path handshake] :or {path "/"}}]
  (.addEndpoint (server-container servlet-context)
    (.. ServerEndpointConfig$Builder
      (create DelegatingJavaxEndpoint path)
      (configurator (proxy [ServerEndpointConfig$Configurator] []
                      (getEndpointInstance [_] (DelegatingJavaxEndpoint.))
                      (modifyHandshake [_ _ _]
                        (when handshake
                          (handshake
                            (.get WebSocketHelpyHelpertonFilter/requestTL))))))
      build)))