Nothing in my mind though really beats the ecosystem around Java of these three in terms of IDE support, tooling and just simplicity in getting code out fast when you don't need low level access to things. Netty really brings great things to Java, and the many mature web frameworks for JVM languages are probably better than anything available for Rust right now. I'm not sure a sane person would write backend for a web site in C++. :P
Anyway I love both Rust and Java 8 and it's great to see them thriving.