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Recompile Java code without restarting the REPL

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Do you tarnish your Clojure with the occasional hint of Java? Have you become indescribably tired of reloading your REPL every time you change anything with a .java suffix? Look no further.

Virgil is a library for live-recompiling Java classes from the REPL. This can be done either manually or by starting a process that watches your source directories for changes in Java files and triggering recompilation when that happens.


Add virgil/virgil dependency to your project.clj or deps.edn. If you plan to use Virgil just as a devtime dependency, then you probably want to add it to a profile/alias which you enable only during development.

(require 'virgil)
;; To recompile once, manually:
(virgil/compile-java ["src"])

;; To recompile automatically when files change:
(virgil/watch-and-recompile ["src"])

The main argument to these functions is a list of directories where Java source files are located. Both functions can accept a list of string :options that is passed to Java compiler, e.g. :options ["-Xlint:all"] to print compilation warnings, and a :verbose flag to print all classnames that got compiled.

watch-and-recompile accepts an optional :post-hook function. You can use it to, e.g., trigger tools.namespace refresh after the classes get recompiled.

Check example directory for a sample project.

Happy tarnishing.

Can I use Virgil in production?

Virgil can compile Java classes at runtime in a production environment the same way as it does during the development, so the answer is yes. However, when you do a release build, it is advised to build real Java classes explicitly during your build step using javac task of your build tool. There are multiple arguments for it:

  • You get extra reliability and assurance that the compiled Java classes will be correctly discoverable by other code.
  • You get one fewer runtime dependency.
  • You won't have to rely on JDK-specific tools like package that might not be available in your production environment (e.g., if it runs on JRE).

Migration from 0.1.9

From version 0.3.0, Virgil no longer provides lein-virgil plugin for Leiningen. Instead, you should add virgil it as a regular dependency to your project and call its functions from the REPL.

Supported versions

Virgil makes sure to support Clojure 1.10+ and JDK 8, 11, 17, 21, 22 (see CI job). Supporting future versions of Java so far required only bumping ASM library dependency, so that shouldn't take long. Please, create an issue if you run into any compatibility problems.


Copyright © 2016-2019 Zachary Tellman, 2022-2024 Oleksandr Yakushev

Distributed under the MIT License