code: public static Charset charset(String charsetName) throws UnsupportedCharsetException{
  		return StrUtil.isBlank(charsetName) ? Charset.defaultCharset() : Charset.forName(charsetName);
  	}
docs: 转换为Charset对象
  @param charsetName 字符集，为空则返回默认字符集
  @return Charset
  @throws UnsupportedCharsetException 编码不支持