Live Data Visualisation with R on the JVM

The problem

Java had the web server and the database driver; R had the plotting. The task was to use both in one process, instead of running a separate R server and passing data between two programs.

What I did & decided

• DataService reads one row from MongoDB per request (Row-1 … Row-100).
• PlotController passes the value to an R function (plot.R) through GraalVM's polyglot support and returns the SVG it draws, with a Refresh: 1 header so the browser asks again every second.
• plot.R keeps the last 100 values and draws them with lattice xyplot().
• An R context runs one thread at a time, so calls into it are synchronised; the Spring controller can still serve many requests.

What came of it

• One process, one start command (mvn spring-boot:run), and a chart that updates once a second.
• The README explains how to import the data into MongoDB and run it from scratch.