code: public static List<String> match(String pattern, String reg, int group) {
  
          List<String> matchGroups = new ArrayList<>();
          Pattern compile = Pattern.compile(reg);
          Matcher matcher = compile.matcher(pattern);
          if (group > matcher.groupCount() || group < 0)
              throw new IllegalGroupIndexException("Illegal match group :" + group);
          while (matcher.find()) {
              matchGroups.add(matcher.group(group));
          }
          return matchGroups;
      }
docs: <p>正则提取匹配到的内容</p>
  <p>例如：</p>
  <p>
  author : Crab2Died
  date   : 2017年06月02日  15:49:51
  
  @param pattern 匹配目标内容
  @param reg     正则表达式
  @param group   提取内容索引
  @return 提取内容集合