code: public static StringBuilder read(Reader reader) throws IOException {
          StringBuilder sb = new StringBuilder();
          read(reader, sb);
          return sb;
      }
docs: 从一个文本流中读取全部内容并返回
  <p>
  <b style=color:red>注意</b>，它并不会关闭输出流
  
  @param reader
  文本输出流
  @return 文本内容
  @throws IOException