My personal experience is that, while Java has a lot of great technologies associated with it, such as Hadoop, they're hard as hell to learn. The problem isn't the systems. It's that large systems in Java become cluttered with accidental complexity, which makes easy things hard to write and read and hard things nearly insurmountable. I'm a major fan of any effort to put support the best parts of the Jawva ecosystem on these new, far better, JVM languages.