Sorting, Pagination, and JPQL

If you are requesting a database list evaluating 10,000 distinct items, querying the entire array down into basic JVM memory will throttle the application server. You must segment massive data streams using pagination.

Pagination via Spring Data

Spring provides specific parameters handling explicit page limits.

public interface ProductRepository extends JpaRepository<Product, Long> {
    Page<Product> findByCategory(String category, Pageable pageable);
}

In the standard @Controller, you simply populate the specific Pageable structure.

// Spring parses URL params natively: ?page=0&size=20&sort=price,asc
@GetMapping("/products")
public Page<Product> loadProducts(Pageable pageable) {
    return productRepository.findByCategory("Electronics", pageable);
}

Custom JPQL Methods

If Derived Methods become overly chaotic, developers revert to explicitly configuring queries using @Query.

public interface UserRepository extends JpaRepository<User, Long> {
    
    // JPQL targets Java Classes, NOT standard SQL tables!
    @Query("SELECT u FROM User u WHERE u.email = :email AND u.active = true")
    Optional<User> searchEmailManually(@Param("email") String email);
}