code: public static void shutdown() {
          try (Socket socket = new Socket(IP_ADDR, getShutDownPort());
               PrintWriter writer = new PrintWriter(socket.getOutputStream());
               BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()))) {
              writer.println(SHUTDOWN);
              writer.flush();
              LOG.info("shutdown服务器命令已发送...");
              String line;
              do {
                  line = reader.readLine();
                  LOG.info("server返回:" + line);
              } while (!SHUTDOWN_ACK.endsWith(line));
              LOG.info("服务器shutdown完毕:" + line);
              LOG.debug("等待较短时间，以便服务端java虚拟机退出.");
              Thread.sleep(500);
          } catch (Throwable t) {
              LOG.error("", t);
          }
      }
docs: 懒加载,可以防止本地执行main方法时总是报找不到配置文件的错误