How to convert Array Result to JSON format when selecting particular column in Query

For converting Query result(Array) to JSON format,

I tried with @ResponseBody annotation and also with produces="application/json" but no changed in output format. I also tried with ObjectMapper() but that output in string format not in key value.I removed my trial which not working.Now I added here my current code.

Here is my code snippet.

InvestigatorModel

package com.demo.model;

import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="investigator")
public class InvestigatorModel implements Serializable{

        private static final long serialVersionUID = 1L;

        @Id
        public Integer ninvestigatorid;
        public String sinvestigatorname;
        public Integer ninstid ;
        public String stitle;
        public Integer ntempinvestigatorid;
        public Integer nempid;
        //getter and setter

InvestigatorController

package com.demo.controller;

import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.demo.model.InvestigatorModel;
import com.demo.services.InvestigatorService;

@RestController
@RequestMapping("/SpaceStudy/SpaceAdmin")

public class InvestigatorController {

    @Autowired
    InvestigatorService investService;

  @CrossOrigin(origins="*") 
  @GetMapping("/AccountMaintenance/LoadInvestigator")   

  public List<InvestigatorModel> findInvestigatorName()
  {
    return investService.findInvestigatorName();

  }
}

InvestigatorService

package com.demo.services;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.demo.model.InvestigatorModel;
import com.demo.repository.InvestigatorRepository;

@Service
public class InvestigatorService 
{
    @Autowired
    InvestigatorRepository investRepo;

    public List<InvestigatorModel> findInvestigatorName()
    {
        return investRepo.findBySinvestigatorname();

    }

}

InvestigatorRepository

package com.demo.repository;
import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;

import com.demo.model.InvestigatorModel;
@Repository
public interface InvestigatorRepository extends JpaRepository<InvestigatorModel, Integer>
{
    @Query("select invest.sinvestigatorname from InvestigatorModel as invest where invest.ninstid=60")
    List<InvestigatorModel> findBySinvestigatorname();
}

My output is like This

Sample output

[
  {
    "sinvestigatorname": "Bargman",

   }
]

How to convert This output into JSON format(key,value) Can any one help me how to do that