I recently ordered and researched the cheapest feature phones (and some smartwatches), looks like half of that market is occupied by Unisoc with the SC6531(E/DA) chipset (from the Spreadtrum company they bought). It uses Mocor OS. The second half of this market is occupied by Mediatek MT6260/MT6261 chipsets. I wrote tools to run my code on these chipsets.

There are also phones on Mocor5 OS, a little more expensive, it's actually Android 4.4 on the Spreadtrum SC7715 chipset.

I didn't find any Java here, but these CPUs have a Jazelle ARM extension to run Java bytecode.

P.S.: There's an old project based on reverse engineered MT6260 firmware: https://github.com/xobs/fernly