... clearly Java doesn't have a ggplot2

JFreeChart[0] is likely what many would reach for in the JVM ecosphere to perform ggplot2-type functionality, though Scala devs might want to use something like scala-chart[1] or similar.

0 - http://www.jfree.org/jfreechart/samples.html

1 - https://github.com/wookietreiber/scala-chart

This software has its own visualization package. See it at

http://haifengl.github.io/smile/visualization.html