I vouch for JVM, specifically:

* Bootique (better Spring Boot),

* Vert.x (reactive framework and libraries for unmatched performance),

* Akka (for distributed coordination, if necessary; though depending on the use case, it might be simpler to just use external services, like Zookeeper or Consul -- Bootique has integration with those)

Honorable mention goes to Netty, which is great for high performance networking, but going so far is rarely needed in most servers.