Replace play.libs.F.Option with Java 8 equivalent

[marcospereira]

Replace play.libs.F.Option and friends with java.util.Optional and friends

[marcospereira]

Here is what I have changed:

1. Code documentation was also updated to remove mentions about F.Option and subclasses of it.
2. The Some class, which was a subclass of F.Option did not complain about null values. Because of that, Optional.ofNullable was used to guarantee the same behavior.
3. Some other small changes were made to cleanup the code, following the boy scout rule defined in contribution guidelines.

---

@dotta there is a problem with the FormSpec, the build will show that. Looks like the form binding is not handling Optional properly. It could be something related with Spring Binder, but I did not had time to investigate further. I'm submitting the PR so that it can be reviewed sooner.

[dotta]

Would it make sense to use the scala-java8-compat library for these kind of conversions? See here.

[dotta]

@marcospereira Great job Marcos!

[marcospereira]

@dotta I've change the PR to use scala-java8-compat. Thanks for pointing that. Anyway, I could not figure out why play.data.FormSpec is failing. Any help here will be appreciated.

[dotta]

@marcospereira LGTM!

Later today I'll see if I can find some time to look into the FormSpec failing test.

[marcospereira]

Ok. I debug the code and figure out the problem now. F.Option extends java.util.Collection and then, our custom GenericConversion was able to find a TypeDescriptor because Spring understands java.util.Collection but not java.util.Optional. From TypeDescriptor. getElementTypeDescriptor():

If this type is an array, returns the array's component type. If this type is a Collection and it is parameterized, returns the Collection's element type. If the Collection is not parameterized, returns null indicating the element type is not declared.

Returns:
the array component type or Collection element type, or null if this type is a Collection but its element type is not parameterized

Throws:
IllegalStateException - if this type is not a java.util.Collection or array type

And this method was being called here:

https://github.com/playframework/playframework/blob/master/framework/src/play-java/src/main/java/play/data/format/Formatters.java#L171

This is now fixed and the build should be green.

[marcospereira]

Rebased.

[dotta]

This is a minor nitpick, but you could use :+ (append) instead of ++ and wrapping the dependencies in a Seq. No need to change this, but I'm pointing it out just in case you didn't know.

[marcospereira]

I did not. Thanks. :-)

[dotta]

This is now fixed and the build should be green.
(extracted from #4692 (comment))

@marcospereira How did you fix it? I can't easily see what is that was changed to fix it.

[marcospereira]

@dotta mostly debugging the code and reading Spring docs. Here is the line that did the trick:

https://github.com/playframework/playframework/blob/master/framework/src/play-java/src/main/java/play/data/format/Formatters.java#L168

Before this commit, it was using targetType.getElementTypeDescriptor(), which does works for java.util.Collection (F.Option was a java.util.Collection), but not for java.util.Optional. targetType.elementTypeDescriptor(source) works because it properly creates a TypeDescriptor for Optional.

[dotta]

@dotta mostly debugging the code and reading Spring docs. Here is the line that did the trick:

https://github.com/playframework/playframework/blob/master/framework/src/play-java/src/main/java/play/data/format/Formatters.java#L168

Before this commit, it was using targetType.getElementTypeDescriptor(), which does works for java.util.Collection (F.Option was a java.util.Collection), but not for java.util.Optional. targetType.elementTypeDescriptor(source) works because it properly creates a TypeDescriptor for Optional.

Got it, thanks! (Wow, that must have been a tricky one to nail down ;-))