How to safely reload server side javascript functions on the fly?

Question

I am experimenting with Nashorn and calling js functions from Java code. I have a WatchService that reloads changed files and reevaluates the ScriptEngine

engine.eval(Files.newBufferedReader(Paths.get(scriptFile), StandardCharsets.UTF_8));

It seems to work fairly well, however, there have been a couple times where I saved the javascript file with unsuspecting typos inside and the subsequent attempt to invoke function

invoker.invokeFunction("printServiceReport", tesla);

causes a javax.script.ScriptException to be thrown thereby killing my running code. Looking for a workable solution to reload logic in real-time without negatively disrupting my application.

Answer 1

Wrap your eval of each code file in a try catch as well as your invokes.

If you need to, you can run through all your functions on reload to see if errors occur - and then use the old version instead if errors are found (if detecting errors at runtime is unacceptable).

We do something similar to that when we reload our serverside scripts.