code: public Server run() throws Exception {
          if (server == null) {
              server = new Server(port);
              String basePath = "/druid";
              buildSwagger(basePath);
              HandlerList handlers = new HandlerList();
              handlers.addHandler(buildContext(basePath));
              server.setHandler(handlers);
              server.start();
          } else {
              throw new IllegalStateException("Server already running");
          }
          return server;
      }
docs: Starts the Druid instance and returns the server it is running on
  
  @return server hosting Druid
  @throws Exception