There are Java alternatives, but I think they are costly. For example ST Microelectronics has this java IDE based on eclipse:
Java SDK
I have no experience with java on microcontrollers, but Java have many similarities (C based language) to C++ (which is more supported with microcontrollers), but it is still C that is dominating. It should be possible to learn this quite fast if you already know Java.
Arduino uses C++ and are easy to use for people inexperience with C/C++.
I suggest you also try the STM32 Java forum to see if there are users already sharing their experiences:
STM32 Java forum
