Java Spring REST API Handling Many Optional Parameters

Question

I'm currently messing around with a Spring Boot REST API project for instructional purposes. I have a rather large table with 22 columns loaded into a MySQL database and am trying to give the user the ability to filter the results by multiple columns (let's say 6 for the purposes of this example).

I am currently extending a Repository and have initialized methods such as findByParam1 and findByParam2 and findByParam1OrderByParam2Desc and etc. and have verified that they are working as intended. My question to you guys is the best way to approach allowing the user the ability to leverage all 6 optional RequestParams without writing a ridiculous amount of conditionals/repository method variants. For example, I want to give the user the ability to hit url home/get-data/ to get all results, home/get-data?param1=xx to filter based on param1, and potentially, home/get-data?param1=xx&param2=yy...&param6=zz to filter on all the optional parameters.

For reference, here is what the relevant chunk of my controller looks like (roughly).

@RequestMapping(value = "/get-data", method = RequestMethod.GET)
public List<SomeEntity> getData(@RequestParam Map<String, String> params) {
    String p1 = params.get("param1");
    if(p1 != null) {
        return this.someRepository.findByParam1(p1);
    }
    return this.someRepository.findAll();
}

My issue so far is that the way I am proceeding about this means that I will basically need n! amount of methods in my repository to support this functionality with n equalling the amount of fields/columns I want to filter on. Is there a better way to approach handling this, perhaps where I am filtering the repository 'in-place' so I can simply filter 'in-place' as I check the Map to see what filters the user did indeed populate?

EDIT: So I'm currently implementing a 'hacky' solution that might be related to J. West's comment below. I assume that the user will be specifying all n parameters in the request URL and if they do not (for example, they specify p1-p4 but not p5 and p6) I generate SQL that just matches the statement to LIKE '%' for the non-included params. It would look something like...

@Query("select u from User u where u.p1 = :p1 and u.p2 = :p2 ... and u.p6 = :p6") 
List<User> findWithComplicatedQueryAndSuch;

and in the Controller, I would detect if p5 and p6 were null in the Map and if so, simply change them to the String '%'. I'm sure there is a more precise and intuitive way to do this, although I haven't been able to find anything of the sort yet.

Answer 1

You can do this easily with a JpaSpecificationExecutor and a custom Specification : https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl/

I would replace the HashMap with a DTO containing all optional get params, then build the specifications based on that DTO, obviously you can also keep the HashMap and build the specification based on it.

Basically:

public class VehicleFilter implements Specification<Vehicle>
{
    private String art;
    private String userId;
    private String vehicle;
    private String identifier;

    @Override
    public Predicate toPredicate(Root<Vehicle> root, CriteriaQuery<?> query, CriteriaBuilder cb)
    {
        ArrayList<Predicate> predicates = new ArrayList<>();

        if (StringUtils.isNotBlank(art))
        {
            predicates.add(cb.equal(root.get("art"), art));
        }
        if (StringUtils.isNotBlank(userId))
        {
            predicates.add(cb.equal(root.get("userId"), userId));
        }
        if (StringUtils.isNotBlank(vehicle))
        {
            predicates.add(cb.equal(root.get("vehicle"), vehicle));
        }
        if (StringUtils.isNotBlank(identifier))
        {
            predicates.add(cb.equal(root.get("identifier"), fab));
        }

        return predicates.size() <= 0 ? null : cb.and(predicates.toArray(new Predicate[predicates.size()]));
    }

// getter & setter
}

And the controller:

@RequestMapping(value = "/{ticket}/count", method = RequestMethod.GET)
public long getItemsCount(
    @PathVariable String ticket,
    VehicleFilter filter,
    HttpServletRequest request
) throws Exception
{
    return vehicleService.getCount(filter);
}

Service:

@Override
public long getCount(VehicleFilter filter)
{
    return vehicleRepository.count(filter);
}

Repository:

@Repository
public interface VehicleRepository extends JpaRepository<Vehicle, Integer>, JpaSpecificationExecutor<Vehicle>
{
}

Just a quick example adapted from company code, you get the idea!

Answer 2

Another solution with less coding would be to use QueryDsl integration with Spring MVC.

By using this approach all your request parameters will be automatically resolved to one of your domain properties and appended to your query.

For reference check the documentation https://spring.io/blog/2015/09/04/what-s-new-in-spring-data-release-gosling#querydsl-web-support and the example project https://github.com/spring-projects/spring-data-examples/tree/master/web/querydsl

Answer 3

You can do it even more easily using Query By Example (QBE) technique if your repository class implements JpaRepository interface as that interface implements QueryByExampleExecutor interface which provides findAll method that takes object of Example<T> as an argument.

Using this approach is really applicable for your scenario as your entity has a lot of fields and you want user to be able to get those which are matching filter represented as subset of entity's fields with their corresponding values that have to be matched.

Let's say the entity is User (like in your example) and you want to create endpoint for fetching users whose attribute values are equal to the ones which are specified. That could be accomplished with the following code:

Entity class:

@Entity
public class User implements Serializable {
    private Long id;
    private String firstName;
    private String lastName;
    private Integer age;
    private String city;
    private String state;
    private String zipCode;
}

Controller class:

@Controller
public class UserController {
    private UserRepository repository;
    private UserController(UserRepository repository) {
        this.repository = repository;
    }

    @GetMapping
    public List<User> getMatchingUsers(@RequestBody User userFilter) {
        return repository.findAll(Example.of(userFilter));
    }
}

Repository class:

@Repository
public class UserRepository implements JpaRepository<User, Integer> {
}