How to use Spring Data JPA methods returning a Stream in a try-with-resources block in Kotlin? - spring

Question

So I want to create a Spring Boot with Spring Data JPA project using Kotlin and lets say I have a Person entity. Lets say like this:
#Entity
public class Person {
private #GeneratedValue #Id Long id;
private String name;
#OneToMany
private List<Person> friends;
…
}
I would create the following interface to be able to use Try-with-Resources and a Stream<Person>.
public interface PersonRepository extends Repository<Person, Long> {
#Query("select p from Person p")
Stream<Person> findAllStream();
}
So normally in my service I would do this:
#Service
class MyService {
#Autowired PersonRepository repository;
List<String> foo() {
try(Stream<Person> stream = repository.findAllStream()) {
return stream.flatMap(p -> p.getFriends().stream())
.map(f -> f.getName())
.collect(Collectors.toList());
}
}
}
Now if you want to do this in Kotlin (The IntelliJ converter doesn't produce valid code). I suppose you would normally do something like:
class MyService #Autowired constructor(val personRepository: PersonRepository) {
fun foo() {
val list = personRepository.findAllStream()
.use {{p -> p.friends.stream()}.map {f -> f.name}}
}
}
Only you cant do that since there is no #use method on stream and you cant call #stream() from a List. So is there any way to do this?

Answer 1

Well, Java 8 support is not yet complete in Kotlin. So you can just declare use on your side like this
inline fun <A : AutoCloseable, R> A.use(block: (A) -> R): R {
try {
return block(this)
} finally {
close()
}
}
The other alternative is to declare it directly on Stream
inline fun <T, R> Stream<T>.use(block: (Stream<T>) -> R): R {
try {
return block(this)
} finally {
close()
}
}
UPD
If you are new to Kotlin you have to notice that extensions are resolved statically:
Extensions do not actually modify classes they extend. By defining an extension, you do not insert new members into a class, but merely make new functions callable with the dot-notation on instances of this class.
See more http://kotlinlang.org/docs/reference/extensions.html#extensions-are-resolved-statically