code: public static String get(String regex, CharSequence content, int groupIndex) {
  		if (null == content || null == regex) {
  			return null;
  		}
  
  		// Pattern pattern = Pattern.compile(regex, Pattern.DOTALL);
  		final Pattern pattern = PatternPool.get(regex, Pattern.DOTALL);
  		return get(pattern, content, groupIndex);
  	}
docs: 获得匹配的字符串
  
  @param regex 匹配的正则
  @param content 被匹配的内容
  @param groupIndex 匹配正则的分组序号
  @return 匹配后得到的字符串，未匹配返回null