How to make a dynamic Spring (Boot) JPA query with paging?

To oversimplify the problem: we have a class/table Wine (table "wines") which has, among other attributes:

• name: String
• description: String
• origin: Origin

... where Origin is another class (with table "origins") with just region: String and country: String.

What I'm trying to make is a search method in my repository for the RestController to use.

The method declaration in the RestController is like this:

@GetMapping("/search")
public Wine searchProduct(
		@RequestParam Optional<String> searchTerm,
		@RequestParam Optional<Origin> origin) {
	// ???
}

What I'm trying to do now is the following: creating a query for the database where the searchTerm is used if given, same with origin. And it should be pageable.
Example:

SELECT * FROM wines JOIN origins ON wines.origin_id = origins.id 
    WHERE (name LIKE $searchTerm OR description LIKE $searchTerm) AND (/*origin check*/)

If no search term is given, the whole "() AND" part should not be in the query. If no Origin is given... you get it.

Things I've tried:

1. (Naively) building a massive query in my repository (implements CrudRepository) like here.

   Page<Wine> findWinesByNameLikeOrDescriptionLikeAndOriginEquals(..., Pageable pageable);

   • Which (apart from being super ugly, especially for more attributes) probably doesn't work because:
     1. It's not defined whether OR or AND are more important (no brackets).
     2. No idea whether I can just shove an "Origins" object in there for it to work.
     3. No idea whether Pageable even works if that's a custom method.

2. Using "Specifications and Querydsl" as suggested by spring.io here.

   • Which I'm just to stupid to understand, especially with those Q classes at the bottom of the post or the _ classes in the beginning. It just seems way too compicated for what it should do.
   • Also there are no pagination options. There is, however, a possible fix like here but I didn't get to it since using those _ and/or Q classes was to much of an overhead to start with.

3. Also this is just an example I found from 2013 which I don't even understand in general but kinda looks like it would be very fitting.

If you find it difficult to understand Specifications, only have those two search parameters and assuming Wine entity has a @ManyToOne to Origin, you can do the following:

    @Query("SELECT w FROM wines w join w.origin o where " +
            "(   :searchTerm is null or " +
            "    w.name like CONCAT('%',:searchTerm ,'%') or " +
            "    w.description like CONCAT('%', :searchTerm ,'%')" +
            ") " +
            "AND (:origin is null or  o = :origin)")
    Page<Wine> searchWines(String searchTerm, Origin origin, Pageable p);

And when you call it,

    wineRepository.searchWines(searchTerm.orElse(null), origin.orElse(null));

So I actually got a solution working! For curious people, here's how I did it:

ProductController.java

@GetMapping("search")
public Page<Wine> searchProducts(
		@RequestParam(name = "text", required = false) String searchTerm,
		@RequestParam(required = false) Origin origin,
		@RequestParam(required = false) Integer page) {
	// generate PageRequest based on Integer page if given:
	Pageable pageRequest = PageRequest.of(page != null ? page : 0, 10);
	if(Objects.isNull(searchTerm) && Objects.isNull(origin)) {
		return wineService.findAll(pageRequest);
	}
	return wineService.searchWines(
			searchTerm,
			origin,
			pageRequest
	);
}

WineService.java

public Page<Wine> searchWines(String searchTerm, Origin origin, Pageable pageable) {
	List<Specification<Wine>> specifications = new LinkedList<>();
	if (searchTerm != null) {
		specifications.add(ProductSpecification.hasSearchStringInNameOrDescription(searchTerm));
	}
	if (origin != null) {
		specifications.add(ProductSpecification.hasOrigin(origin));
	}
	if (specifications.isEmpty()) {
		return wineRepository.findAll(pageable);
	} else {
		Specification<Wine> query = Specification.where(specifications.remove(0));
		for (Specification<Wine> wineSpecification : specifications) {
			query = query.and(wineSpecification);
		}
		return wineRepository.findAll(query, pageable);
	}
}

as an example, here's the specification for the name/description string:

ProductSpecification.java

public static Specification<Wine> hasSearchStringInNameOrDescription(String input) {
	final String searchTerm = input.toLowerCase();
	return (root, criteriaQuery, criteriaBuilder) -> {
		log.info("SearchTerm: " + searchTerm);
		Predicate pName = criteriaBuilder.like(
				criteriaBuilder.lower(root.get(Wine_.NAME)),
				"%" + searchTerm + "%"
		);
		Predicate pDescription = criteriaBuilder.like(
				criteriaBuilder.lower(root.get(Wine_.DESCRIPTION)),
				"%" + searchTerm + "%"
		);
		return criteriaBuilder.or(pName, pDescription);
	};
}

The generation of those Wine_ classes is automatic with a Maven plugin. See this.
Additionally, for the conversion of request body pieces to complex objects like Origin, you need to include a converter class like here.