2014
http://www.infoq.com/presentations/java8-evolution
http://www.slideshare.net/jpaumard/50-new-things-you-can-do-with-java-8

books
Konda - All about Java 8 Lambdas

comprehensive look
https://dzone.com/articles/j%CE%BBv%CE%BB-8-a-comprehensive-look
https://dzone.com/articles/j%CE%BBv%CE%BB-8-a-comprehensive-look-part-11-lambdas-under
https://dzone.com/articles/j%CE%BBv%CE%BB-8-a-comprehensive-look-part-12-insight-into-s

optional
https://habrahabr.ru/post/347480/
https://habrahabr.ru/post/347576/
https://habrahabr.ru/post/347748/
https://habrahabr.ru/post/347836/
https://habrahabr.ru/post/350904/

java.util.function
    Function
    Supplier
    Consumer