使用java的Calendar对象获得当前日期

/**
   * @param flag true：开始日期；false：结束日期
   * @return
   */
  public static String getLastQuarterTime(boolean flag){
    SimpleDateFormat shortSdf = new SimpleDateFormat("yyyy-MM-dd");
    SimpleDateFormat longSdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
     
    String resultDate="";
    Date now = null;
    try {
      Calendar calendar = Calendar.getInstance();
      int currentMonth = calendar.get(Calendar.MONTH) + 1;
      //true：开始日期；false：结束日期
      if(flag){
        if (currentMonth >= 1 && currentMonth <= 3)
          calendar.set(Calendar.MONTH,0);
        else if (currentMonth >= 4 && currentMonth <= 6)
          calendar.set(Calendar.MONTH,3);
        else if (currentMonth >= 7 && currentMonth <= 9)
          calendar.set(Calendar.MONTH,6);
        else if (currentMonth >= 10 && currentMonth <= 12)
          calendar.set(Calendar.MONTH,9);
        calendar.set(Calendar.DATE,1);
         
        now = longSdf.parse(shortSdf.format(calendar.getTime()) + " 00:00:00");
      }else{
        if (currentMonth >= 1 && currentMonth <= 3) {
          calendar.set(Calendar.MONTH,2);
          calendar.set(Calendar.DATE,31);
        } else if (currentMonth >= 4 && currentMonth <= 6) {
          calendar.set(Calendar.MONTH,5);
          calendar.set(Calendar.DATE,30);
        } else if (currentMonth >= 7 && currentMonth <= 9) {
          calendar.set(Calendar.MONTH,8);
          calendar.set(Calendar.DATE,30);
        } else if (currentMonth >= 10 && currentMonth <= 12) {
          calendar.set(Calendar.MONTH,11);
          calendar.set(Calendar.DATE,31);
        }
        now = longSdf.parse(shortSdf.format(calendar.getTime()) + " 23:59:59");
      }
      calendar.setTime(now);// 设置日期
      calendar.add(Calendar.MONTH,-3);
      resultDate = longSdf.format(calendar.getTime());
       
    } catch (Exception e) {
      ;
    }
    return resultDate;
  }