I’m developing an API for college courses and I want the requests to be able to handle multiple query parameters that refine the search in different ways. Example with 2 parameters:

http://url.com/api/courses/search?subject=CSCI&number=1302

I’m trying to figure out a way I can handle all the different parameters for the search header in one method in the service class. I want the parameters to be able to be in any order, and with any number of parameters (a request may have 0 or as many as the API supports). Right now, the code is only set up to support one parameter at a time. The subject header accepts any parameters and the List gets unpacked in the CourseService.java. I assume there’s an easier way to do this than writing a new if case for each combination of parameters?

Perhaps something like this pseudocode, with each one further refining the past result:

search(fullDatabase, param1);
search(search1, param2);
search(search2, param3);

Here’s my current code:

CourseController.java

@RestController
@RequestMapping("/api/courses")
public class CourseController {
    
    @Autowired
    private CourseService courseService;

    @RequestMapping("/search")
    public List<Course> searchCourses(@RequestParam Map<String, String> params) {
        return courseService.getCourses(params);
    }
}

CourseService.java

@Service
public class CourseService {
    
    @Autowired
    private CourseRepository courseRepository;

    /** Handles all logic for query parameters. */
    public List<Course> getCourses(Map<String, String> params) {
        if (params.keySet().contains("crn")) {
            return courseRepository.findByCrn(params.get("crn"));
        } else if (params.keySet().contains("subject")) {
            return courseRepository.findBySubject(params.get("subject"));
        } else if (params.keySet().contains("number")) {
            return courseRepository.findByNumber(params.get("number"));
        } else if (params.keySet().contains("seats")) {
            return courseRepository.findBySeats(params.get("seats"));
        }
        throw new QueryArgumentException(null, getClass(), params);
    }
}

CourseRepository.java

@Repository
public interface CourseRepository extends JpaRepository<Course, Integer> {

    @Query("FROM Course WHERE crn = ?1")
    List<Course> findByCrn(String crn);

    @Query("FROM Course WHERE subject = ?1")
    List<Course> findBySubject(String subject);

    @Query("FROM Course WHERE number = ?1")
    List<Course> findByNumber(String number);

    @Query("FROM Course WHERE department = ?1")
    List<Course> findByDepartment(String department);
    
    @Query("FROM Course WHERE seats >= ?1")
    List<Course> findBySeats(String seats);
}