Support Java 8 Streams on JpaSpecificationExecutor [DATAJPA-906]

[spring-projects-issues]

Tarek Nabil opened DATAJPA-906 and commented

Currently, the findAll(…) methods of JpaSpecificationExecutor only supports returning List and Page. It would be very useful if support for returning Java 8 streams could be added. For example, two findAllAndStream(…) methods could be added that take either a Specification or a Specification and Sort

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5 votes, 7 watchers

[spring-projects-issues]

Oliver Drotbohm commented

This unfortunately will have to wait for a 2.0 revamp as a Stream in the method signature would render the interface unloadable on versions of Java < 8

[spring-projects-issues]

Tarek Nabil commented

Well, is there a reason why Specification support was implemented this way versus just recognising methods declared with Specification parameters as is the case with finder methods?
Would it be possible to automatically recognise finder methods that are declared with Specification parameters and support Stream return types for them?

[spring-projects-issues]

Oliver Drotbohm commented

Yes, there's a clear separation between the query methods that represent static query definitions (either derived from the method name or explicitly declared) and the support for dynamic predicates (Querydsl, specifications). Blurring the line between the two opens up a pandora's box of ambiguities (how would you even combine a CriteriaQuery defined through a Specification and a manually defined JPQL query?)

[spring-projects-issues]

Tarek Nabil commented

So, can you think of another way to allow streaming Specification queries without breaking pre-JDK 8 compatibility?

[spring-projects-issues]

HerrDerb commented

I'm looking forward to this feature. Currently I have to feed a StreamSupplier with pages, forcing me to load sub collection eagerly as the session is not valid any more once I get the item from the Stream

[spring-projects-issues]

Jens Schauder commented

@HerrDerb: Streams wouldn't really change anything about the order of loading, so I guess I'm not sure what you are hoping for here. This is really just about the available API

[spring-projects-issues]

Jens Schauder commented

In general:

We can't just add Stream<T> findAll(Specification) because it would be ambiguous with the existing methods.

The options I see would be

• change the method name to something like findAllAsStream
• provide a new interface StreamingJpaSpecificationExecutor with the same methods but Stream as return type instead of List.

I don't really like either one because they create quite some noise without offering much of an improvement since the execution model would be still the same (all records get loaded and then just presented as a List which the user can trivially implement on their own.

But all is not lost, there is still DATAJPA-1189 which might offer the opportunity to implement this as well

[spring-projects-issues]

HerrDerb commented

@Jens Schauder Ah sorry, there is nothing about the order.In a service of mine, I simply wrapped the Page findAll(Specification,Pageable) method to return a stream, which forces me to load sub collection eagerly

[spring-projects-issues]

Jens Schauder commented

@HerrDerb the same would apply to any built-in method provided by Spring Data

[spring-projects-issues]

Jens Schauder commented

There doesn't seem to be a good solution for this apart from what might come out of DATAJPA-1189