add throws annotation FPromiseHelper#get

[kamekoopa]

add throws annotation.
Promise#get() throws TimeoutException, but can't know it from java api.
excepion handling is inconvenience.

[cloudbees-pull-request-builder]

play2-master-PRs #247 SUCCESS
This pull request looks good

[jroper]

Not sure about this. I think I'd rather document that it throws a TimeoutException.

[kamekoopa]

try {
  promise.get();
} catch (TimeoutException e){
  //error handling
}

The above is compile error, because Promise#get() method does not have the throws signature and a TimeoutException is a checked exception.
In order to handle an error, have to write like the below and I have felt inconvenient this is.

try {
  promise.get();
} catch(Throwable e){
  if (e instanceof TimeoutException){
    //error handling
  }
}

[richdougherty]

I think the best solution is if get() threw an unchecked exception, but that would be an API change. (Adding a throws annotation is an API change too.)

[jroper]

Let's make it throw an unchecked exception, create a new TimeoutException class that extends RuntimeException, and wraps TimeoutException thrown by promise.get().

[jroper]

@kamekoopa are you able to do this?

[kamekoopa]

@jroper I feel good your idea.

I made an attempt to make modifications perform the its idea in a framework side.
But if you cannot accept this by reasons of influence size and so on, I intend to solve it in the application side.

[jroper]

@kamekoopa It seems I missed your last comment 7 months ago.

The changes you've made are good, except for one thing, the play.core package is intended for internal APIs. If you move PromiseTimeoutException to the F class, then we should be good to go.

There's also been extensive refactoring of Promise since you made the original changes, so it might be a bit of work to rebase this on the current master. Additionally, once you've done the work, would you be able to squash your commits?

If you're not in a position to be able to do these updates, just let me know.

[lightbend-cla-validator]

Hi @kamekoopa,

Thank you for your contribution! We really value the time you've taken to put this together.

Before we proceed with reviewing this pull request, please sign the Typesafe Contributors License Agreement:

http://www.typesafe.com/contribute/cla

[kamekoopa]

@jroper Thank you for replying!

According to your comment, I performed rebase and squash of commits.

[kamekoopa]

@typesafehub-validator I had signed the CLA.