why not both Future and CompletionHandler?

[Jitendra Kotamraju]

There is also similar API ListenableFuture [1] in Guava libraries.  I 
haven't seen the CompletionFuture, but I guess it can be subtype of 
ListenableFuture. Regardless of NIO2, it would be good have this API in 
SE and it will be quite useful to JAX-RS/JAX-WS API.

Jitu
[1]http://guava-libraries.googlecode.com/svn-history/r224/trunk/javadoc/com/google/common/util/concurrent/ListenableFuture.html