How to properly handle empty resultset with Hibernate and Spring Boot

Question

I have a Spring app that is using Hibernate and the Spring Data JPA\'s CrudRepository. Everything seems to work properly if the data that was queried for exists in

Answer 1

None of the spring crud repository find methods throw an exception if no results are returned. They all return nulls. Since you are getting a null pointer exception on the server side you must be trying to perform an operation on the returned value without checking whether it's null first.

Answer 2

Inspect the return value, if it's not null, return some representation of it as a 200 OK response. Otherwise, return a 404 Not Found. In the end, you would have a controller like:

@RequestMapping(...)
public ResponseEntity<?> getOne(...) {
    Something something = repository.findOne(...);
    if (something == null)
        return ResponseEntity.notFound().build();

    return ResponseEntity.ok(something);
}

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You can refactor the preceding code to incorporate Java 8's Optional<T>, as JB Nizet mentioned in the comments. Basically, Optional<T> is just a container that may or may not hold a value of type T. You can use this type as the return type of Spring Data JPA methods, something like the following:

public interface SomethingRepository extends CrudRepository<Something, Long> {
    Optional<Something> findById(Long id);
}

Then define one exception for 404 Not Found:

@ResponseStatus(HttpStatus.NOT_FOUND)
public class NotFoundException extends RuntimeException {}

If you throw an exception of type NotFoundException in your controllers, Spring MVC's exception resolver would catch that exception and convert it to a 404 Not Found HTTP response.

Finally your controller would be like:

@RequestMapping(...)
public Something getOne(...) {
    return repository.findById(id).orElseThrow(NotFoundException::new);
}

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For more detailed discussions on:

• Spring Data JPA's Optional<T> support, read here.
• Spring MVC's exception resolvers, read here.
• Java 8's Optional<T>, read here.
• REST best practices, you can check out the REST in Practice book.