I'am certain they didn't test the versions that got merged the last two days (for example the scala version has a working db test now). So we will probably see some improvements in the next version.
The scala version uses val, which ist like final in java. final enables the JVM to cache this object an run optimizations. So I suspect the object creation only happens once in the scala case, whereas in the java case on every request. I think this is happening here which results in much better performance for the scala version.
But maybe I am wrong and the difference stems only from implementation differences in the controller etc. I'm a php guy and don't know the jvm or scala very well. ;o)
EDIT: @json performance difference:
Seems to me like they tested these two versions:
Java - https://github.com/TechEmpower/FrameworkBenchmarks/blob/5203...
Scala (the version with the not working db) - https://github.com/TechEmpower/FrameworkBenchmarks/blob/b89f...
The scala version uses val, which ist like final in java. final enables the JVM to cache this object an run optimizations. So I suspect the object creation only happens once in the scala case, whereas in the java case on every request. I think this is happening here which results in much better performance for the scala version.
But maybe I am wrong and the difference stems only from implementation differences in the controller etc. I'm a php guy and don't know the jvm or scala very well. ;o)