code: public static PushbackInputStream toPushbackStream(InputStream in, int pushBackSize) {
  		return (in instanceof PushbackInputStream) ? (PushbackInputStream) in : new PushbackInputStream(in, pushBackSize);
  	}
docs: 转换为{@link PushbackInputStream}<br>
  如果传入的输入流已经是{@link PushbackInputStream}，强转返回，否则新建一个
  
  @param in {@link InputStream}
  @param pushBackSize 推后的byte数
  @return {@link PushbackInputStream}
  @since 3.1.0