sql mapping to json object

I am looking for a better approach of mapping my query to json object.

Structure of json object is -

{
   "year":"2020",
   "month":[
      {
         "name":"January",
         "month":"1",
         "payroll_dates":[
            "1",
            "2"
         ],
         "holiday_dates":[
            "3",
            "4"
         ]
      },
      {
         "name":"Feburary",
         "month":"2",
         "payroll_dates":[
            "1",
            "2"
         ],
         "holiday_dates":[
            "3",
            "4"
         ]
      },
      {
         "name":"March",
         "month":"3",
         "payroll_dates":[
            "1",
            "2"
         ],
         "holiday_dates":[
            "3",
            "4"
         ]
      },
      {
         "name":"April",
         "month":"4",
         "payroll_dates":[
            "1",
            "2"
         ],
         "holiday_dates":[
            "3",
            "4"
         ]
      },
      {
         "name":"May",
         "month":"5",
         "payroll_dates":[
            "1",
            "2"
         ],
         "holiday_dates":[
            "3",
            "4"
         ]
      }
   ]
}

and database design is :

   id | calendarDt | year | month | day | calendarType
   1. | 2020-1-25  | 2020 | 1     | 25  | Holiday
    2 | 2020-1-22  | 2020 | 1     | 22  | Holiday
    3 | 2020-1-13  | 2020 | 1     | 13  | Payday

These are the details of january month for holiday and payday.

The java code i have used is :

created a list for each month for holiday.
Created a list for each month for payroll.
Created an object for each month.
And then set the list in the month object.

Is there a better approach for doing it in java?

    List<String> payrollStringJan= new ArrayList<String>();
	List<String> holidayStringJan = new ArrayList<String>();
	Month janMonth = new Month();
   
    for (Calendar item: payrollCalendarList) {

		switch(item.getMonth()) {

		case 1:
			populateMonthObject(item, payrollStringJan, 
            holidayStringJan);
			break;

          }

         	private void populateMonthObject(UhgCalendar item, 
         List<String> payrollString, List<String> holidayString) {
	if("Payday".equals(item.getCalendarType())) {
		payrollString.add(Integer.toString(item.getDay()));
	}
	if("Holiday".equals(item.getCalendarType())) {
		holidayString.add(Integer.toString(item.getDay()));
	}
}

Json pojo -

       public class PayrollCalendar {

    @JsonProperty("year")
    private String year;
    @JsonProperty("month")
    private List<Month> month = null;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();
 //getter setter follow
} 

    public class Month {

    @JsonProperty("name")
    private String name;
    @JsonProperty("month")
    private String month;
    @JsonProperty("payroll_dates")
    private List<String> payrollDates = null;
    @JsonProperty("holiday_dates")
    private List<String> holidayDates = null;
    //getter setter follow
}
}

First of all, I want to understand why the database is designed so. The database can just have calendar date and calendar type. If you want the holiday/Payday in a given month or few months or in a year, you can write the query easily.

In terms of Json object, it can simply have a payday array and a holiday array if the client wants all the dates and I don't think response will be too big for this use-case.