根据年份和季度获取该季度的起始日期

 /**
  * 获取季度的起始值
  * @param year 年份值
  * @param num	季度值
  * @return
  */
 public static String[] getCurrQuarter(int year,int num) {
     String[] s = new String[2];
     String str = "";
     // 设置本年的季
     Calendar quarterCalendar = null;
     quarterCalendar = Calendar.getInstance();
     quarterCalendar.set(Calendar.YEAR,year);
     switch (num) {
         case 1: // 本年到现在经过了一个季度，在加上前4个季度
             quarterCalendar.set(Calendar.MONTH, 3);
             quarterCalendar.set(Calendar.DATE, 1);
             quarterCalendar.add(Calendar.DATE, -1);
             str = DateUtils.formatDate(quarterCalendar.getTime(), "yyyy-MM-dd");
             s[0] = str.substring(0, str.length() - 5) + "01-01";
             s[1] = str;
             break;
         case 2: // 本年到现在经过了二个季度，在加上前三个季度
             quarterCalendar.set(Calendar.MONTH, 6);
             quarterCalendar.set(Calendar.DATE, 1);
             quarterCalendar.add(Calendar.DATE, -1);
             str = DateUtils.formatDate(quarterCalendar.getTime(), "yyyy-MM-dd");
             s[0] = str.substring(0, str.length() - 5) + "04-01";
             s[1] = str;
             break;
         case 3:// 本年到现在经过了三个季度，在加上前二个季度
             quarterCalendar.set(Calendar.MONTH, 9);
             quarterCalendar.set(Calendar.DATE, 1);
             quarterCalendar.add(Calendar.DATE, -1);
             str = DateUtils.formatDate(quarterCalendar.getTime(), "yyyy-MM-dd");
             s[0] = str.substring(0, str.length() - 5) + "07-01";
             s[1] = str;
             break;
         case 4:// 本年到现在经过了四个季度，在加上前一个季度
             str = DateUtils.formatDate(quarterCalendar.getTime(), "yyyy-MM-dd");
             s[0] = str.substring(0, str.length() - 5) + "10-01";
             s[1] = str.substring(0, str.length() - 5) + "12-31";
             break;
     }
     return s;
 }

测试

 @Test
 public void run26(){
     String[] currQuarter = DateUtils.getCurrQuarter(2021, 1);
     System.out.println(JSONUtil.toJsonStr(currQuarter));
 }
// console...
["2021-01-01","2021-03-31"]