code: public static PushbackReader getPushBackReader(Reader reader, int pushBackSize) {
  		return (reader instanceof PushbackReader) ? (PushbackReader) reader : new PushbackReader(reader, pushBackSize);
  	}
docs: 获得{@link PushbackReader}<br>
  如果是{@link PushbackReader}强转返回，否则新建
  
  @param reader 普通Reader
  @param pushBackSize 推后的byte数
  @return {@link PushbackReader}
  @since 3.1.0