convert datetime format from string

ApexUtil2.cls

  /**
   * convert datetime from string
   * @param String datetimeStr : datetime formart string. for example 2015/6/18 11:11
   * @return Datetime : 
   */
  public static Datetime convertDatetimeFromStr( String datetimeStr ) {
    Date dateConv = null;
    Time timeConv = Time.newInstance(0, 0, 0, 0);
    List<String> dt = String.ValueOf(datetimeStr).split('\\-|\\/|\\s|T', 4);
    if(dt.size() > 2) {
      dateConv = Date.newInstance(Integer.ValueOf(dt.get(0)), Integer.ValueOf(dt.get(1)), Integer.ValueOf(dt.get(2)));
      if(dt.size() > 3) {
        List<String> tm = String.valueOf(dt.get(3)).split(':', 3);
        if(tm.size() == 3) {
          timeConv = Time.newInstance(Integer.valueOf(tm.get(0)),Integer.valueOf(tm.get(1)),Integer.valueOf(tm.get(2)),0);
        } else if (tm.size() == 2) {
          timeConv = Time.newInstance(Integer.valueOf(tm.get(0)),Integer.valueOf(tm.get(1)),0,0);
        }
      }
    }
    return (dateConv != null) ? Datetime.newInstance(dateConv, timeConv) : null;
  }