For quite a long time jServer was based on Jetty 9.
A new version which is based on Jetty 11 is soon to be released. This is a big update. It also required rewriting the doclet tool from scratch (it is the tool that generates the XML from the Java libraries).
It is Java 11 indeed. For now it will only be used when building Java 11+ libraries. The new Java modules system makes all kinds of things more complicated so I prefer not to immediately replace the current one. BTW, the new doclet API is one of the ugliest / most opaque APIs that I've worked with. I guess that they designed it like this in order to make it future proof.
For quite a long time jServer was based on Jetty 9.
A new version which is based on Jetty 11 is soon to be released. This is a big update. It also required rewriting the doclet tool from scratch (it is the tool that generates the XML from the Java libraries).
Jetty 9 was very fast and Jetty 11 will be even faster.
It is not something that you can notice from a simple web page. I haven't done excessive performance tests. In most cases the bottleneck will not be the web server itself.