您可以通过在Spring Data JPA中使用Spring Data JPA投影来实现这一点。
创建自定义Repository方法，如下所示

@Repository
public interface PopulationRepository extends JpaRepository<Population, Long> {

@Query("select new com.example.Count(country, state, count(p) )
       from Population p
       group by p.country, p.state")
public List<Count> getCountByCountryAndState();

}

此外，您还必须在Count类中定义特定的构造函数，以处理此投影

private static class Count {
 private String country;
 private String state;
 private long count;
 
 //This constructor will be used by Spring Data JPA 
 //for creating this class instances as per result set
 public Count(String country,String state, long count){
   this.country = country;
   this.state = state;
   this.count = count;
 }
}

您可以使用JpaRepository接口。示例：

@Repository
public interface PopulationRepository extends JpaRepository<Population, Long> {

    public int countAllByCountryAndState(String countryName, String stateName);

}

为您服务：

@Service
@Transactional
public class PopulationService {

    @Autowired
    private PopulationRepository populationRepository;

    public int countPopulationByCountryAndState(String countryName, String stateName) { 

         return populationRepository.countAllByCountryAndState(countryName, stateName);
    }

}

对不起，我犯了个错误，它可以更简单.我编辑了我的代码.