Get a REPL On Your Current Java Project

I like to test things out interactively, so I love working with languages that provide a REPL. I’m currently working on a Java project, but Java doesn’t have a REPL. Several languages built on top of the JVM do have them, and these langauges can access the Java classes on their classpaths. Groovy, Scala and Clojure are just three such examples, that I happen to work with.

I got this tip from this response on a Stackoverflow.com post. His tip was for Scala, which looks like this:

scala -cp target/classes:`/usr/bin/mvn \
dependency:build-classpath \
| grep "^[^\[]"`

The bit between the backticks runs a Maven goal that outputs the jars that your project depends on, and then extracts just the list of fully-qualified jar files to append to the Scala classpath. If you want to use Groovy for your REPL, it would look like this:

groovysh -cp target/classes:`/usr/bin/mvn \
dependency:build-classpath \
| grep "^[^\[]"`

Similarly, if you’d rather use Clojure, do this:

java -cp target/classes:`/usr/bin/mvn \
dependency:build-classpath \
| grep "^[^\[]"`:/path/to/clojure.jar clojure.main

(Note: In the examples above, I’ve split the code across multiple lines for clarity. In reality, it can be all on one line.)

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3 Responses to Get a REPL On Your Current Java Project

  1. Zack Power says:

    I would recommend just running the scala maven plugin(http://davidb.github.io/scala-maven-plugin/example_console.html) instead. Then alll you have to do is run:
    mvn scala:console

    • joeygibson says:

      If you have a Scala project, and are using Maven, then I agree. What I was presenting is how to have a poor-man’s REPL on projects that don’t use a REPL-enabled language.

  2. Adam says:

    I’d look at something like JRebel… Basically turns the JVM into a giant REPL.

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