2015-10-17 18:54 GMT+02:00 Sven Linstaedt <sven.linstaedt@gmail.com>:
Hi John
most, if not all Java 8 lambda types are not serializable afaik (sure, one can specify custom serializable lambdas, but I guess this happens rather rarely), so assigning a lambda typed bean a serializable context will probably always cause problems. Even the lamda type itself is serializable, it does not mean it's closure is. Even though application scoped lambda beans are in general no problem at all, most other contexts are. So the question is, whether to allow lambda typed bean to have any serializable scope at all.
java.lang.invoke.SerializedLambda is done for that so should be
Don't get me wrong. I am a huge fan of Java 8 and functional programming in general, but I think FP's way of expressive design somehow collides with CDI's rather declarative style. At least for non-SPI code.
Same here, I think a good API should deserve it. Being able to bind in an extension or through an event not needed a SPI file a lambda would be great but I think we are out of CDI - as backbone - scope there. Maybe doing a proto using custom events can help to play with it and see what we can do of it.Best regardsSven
-- sent by phoneSven,
I'm a little curious, why do they need to avoid serializable contexts? In all honesty, I use app scoped functions, predicates in my code, at least in a couple of places. Lambdas are specifically meant for operations, not data, so they should be in a highly reusable scope (in my opinion at least).
On the flip side, I have a hard time justifying needing to provide injectable beans for lambdas since good encapsulation should indicate they're only used in a single spot.
John
On Sat, Oct 17, 2015 at 7:51 AM Sven Linstaedt <sven.linstaedt@gmail.com> wrote:
Just one question: Who is on charge and is able of managing this unmanaged instances, e.g. lifecycle, serialization, concurrency (e.g. when dealing with closures)?
Functional programming and DI seem to be somehow disjunct in this case. E.g. manually setting up observers seem to better fit extension than normal application code.
On the other side, specifying producer methods or fields, that are injectable and return lambda expressions seems to be a no brainier for CDI, is not it? As long as they are not scoped in a serializable context.
Have a nice weekendSven
-- sent by phone_______________________________________________In brainstorming mode about fun that could be made possible with Java 8 and Java EE.
Question in my mind is: is there some way we could make it possible for Lambdas or Method Refs to be CDI beans?
It goes against the grain obviously as CDI creation is very much a “Don’t call us, we’ll call you” kind of thing. The VM dynamically creates a wrapper object around the Lambda or method reference and it implements the given interface.
To make it work, there would need to be some non-producer method way of saying “put this thing in the context with these qualifiers”.
Imagine a method somewhere that would allow you to:
public <T> void addObserver(java.util.function.Consumer<T> observer, Annotation... qualifiers);
Then you could take advantage as follows:
final List<URI> uris = new ArrayList<>();
// @Observes URI
addObserver((Consumer<URI>) uris::add);
// @Observes Thread
addObserver(Runtime.getRuntime()::addShutdownHook);
// @Observes Runnable
addObserver((Consumer<Runnable>) Executors.newFixedThreadPool(3)::submit);
// @Observes URI
addObserver((Consumer<URI>) System.out::println, new AnnotationLiteral<Fine>() {
});
// @Observes Handler
final Logger logger = Logger.getLogger("somewhere");
addObserver(logger::addHandler); // add handlers via event
// @Observes @Fine String
addObserver((Consumer<String>) logger::fine, new AnnotationLiteral<Fine>() {});
}
-David
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