如何将具有内容的TreeMap转换为JSON格式Spring REST Controller JAVA

Question

Hello I have a code where I want to expose my Collection as JSON format. I thought Spring does it automatically. Here is the code:

@RestController
    public class BirthdayController  extends BaseController{

        @RequestMapping("/api/v1/birthday")
        public TreeMap<Integer, TreeMap<Integer, ArrayList<BirthdayDetails>>> getBirthdays(@RequestParam(value="startYear") Integer startYear,
                                  @RequestParam(value="startMonth") Integer startMonth,
                                  @RequestParam(value="endYear") Integer endMonth,
                                  @RequestParam(value="endMonth") Integer endYear) {
            BirthdayServiceImpl birthdayService = new BirthdayServiceImpl();
            return birthdayService.getBirthdaysBetweenDate(startMonth, startYear, endMonth, endYear);
        }
    }

I get only empty {} on accessing endpoint

Answer 1

try,

@RequestMapping("/api/v1/birthday")
        public @ResponseBody TreeMap<Integer, TreeMap<Integer, ArrayList<BirthdayDetails>>> getBirthdays(@RequestParam(value="startYear") Integer startYear,
                                  @RequestParam(value="startMonth") Integer startMonth,
                                  @RequestParam(value="endYear") Integer endMonth,
                                  @RequestParam(value="endMonth") Integer endYear) {
            BirthdayServiceImpl birthdayService = new BirthdayServiceImpl();
            return birthdayService.getBirthdaysBetweenDate(startMonth, startYear, endMonth, endYear);
        }