In case some of you aren’t aware: we have a Java library to help sign Waves transactions and interact with nodes: WavesJ.
Github page: https://github.com/wavesplatform/WavesJ/ . It has some usage examples.
Maven repository page: https://mvnrepository.com/artifact/com.wavesplatform/wavesj
I’m now adding support for newest features such as scripts, base64, and string data entries.
Ideas and pull requests are welcome!