The value of this is far overstated. You can think of your server as being composed of async queues and thread pools, even in node. About the only thing in a stack that truly is async is connection handling via epoll. Mysql itself is a big threadpool, bounded by the number of cores and table locking.

The jvm has amazing threading support, doubly so if you use it with a language like scala or clojure. You can and should handle the connections asynchronously and use a thread pool for things like db access. It works well, people have done this with the jvm for years.