code: public static int read(Reader reader, StringBuilder sb) throws IOException {
          char[] cbuf = new char[BUF_SIZE];
          int count = 0;
          int len;
          while (-1 != (len = reader.read(cbuf))) {
              sb.append(cbuf, 0, len);
              count += len;
          }
          return count;
      }
docs: 从一个文本流中读取全部内容并写入缓冲
  <p>
  <b style=color:red>注意</b>，它并不会关闭输出流
  
  @param reader
  文本输出流
  @param sb
  输出的文本缓冲
  @return 读取的字符数量
  @throws IOException