Spark was fine, but was abandoned. Which means it was stuck using an end-of-life’d version of Jetty. Which meant that we could no longer pass security audits.
Whereas Javalin continues to get frequently updated.
Spark ruined me. Everyone expects Spring, but dealing with Spring and all the pointless annotation magic is a misery; I find myself longing to just use Spark and forgo all that crap.
I suppose I'll try Javalin then next time I have the choice.