code: public static String readAll(File file) throws RuntimeException {
          try (FileInputStream inputStream = new FileInputStream(file)) {
              return IOUtils.toString(inputStream, Charset.forName("utf-8")).trim();
          } catch (IOException io) {
              throw new RuntimeException(io);
          }
      }
docs: Read a small text file, and return the whole content.
  读取文本文件返回文本文件所有内容
  
  @throws RuntimeException file reading failed.