Question

What techniques that people have found useful using Clojure, Scala, JRuby, build tools, etc. to retrofit a Java project with a REPL to quickly experiment?

I often need to work with plain old Java projects (POJO projects?) and miss having a REPL. Other SO questions address this topic, but these are several years old and the responses are dated.

I’ll start by contributing a few techniques that I’ve used to solve this problem.

Answer 1

If the project uses Maven, the gmaven plugin and accompanying mvn groovy:shell is helpful, although getting it configured correctly can be challenging.

For those projects not using Maven, a common pattern is to include dependencies in a lib folder and manage them manually. For these, I’ve used groovy:

groovysh -cp `echo lib/*.jar | sed 's/ /:/g'`

…or clojure:

java -cp /usr/local/Cellar/clojure/1.3.0/clojure-1.3.0.jar:`echo lib/*.jar | sed 's/ /:/g'` clojure.main

The default Clojure wrapper can also be enhanced with rlwrap.