I have an existing solution written in Java which I would love to run on OpenWrt routers. Will OpenWrt even run Java without installing a lot of dependencies? Anyone ever tried
Since your goal is to get the existing solution running on the router, and not explicitly get a JVM running on the router, I would suggest going the other way:
compile the Java code to native! This also has the potential to be just as fast a C code.
There is an article in Linux journal about this.
If not your cup of tea, JAMVM seems a better fit for a small system such as OpenWRT.