code: public static boolean isLan() {
          if (lan == null) {
              String lanReferenceHost = null;
              try {
                  lanReferenceHost = XianConfig.get(LAN_REFERENCE_HOST_CONFIG, DEFAULT_LAN_REFERENCE_HOST);
                  System.out.println(LAN_REFERENCE_HOST_CONFIG + "=" + lanReferenceHost);
                  InetAddress build = Inet4Address.getByName(lanReferenceHost);
                  lan = build.isReachable(500);
              } catch (UnknownHostException unknownHost) {
                  System.out.println("Unknown host: " + lanReferenceHost + ". So we judge the current network as non-lan.");
                  lan = false;
              } catch (IOException e) {
                  throw new RuntimeException(e);
              }
              System.out.println("LAN=" + lan);
          }
          return lan;
      }
docs: Check if your application runs in the LAN network environment. See {@link #LAN_REFERENCE_HOST_CONFIG} and {@link #DEFAULT_LAN_REFERENCE_HOST}