How do I recompile and reload Java source code while `lein repl` is running?

Question

I have a Clojure project, and I'm using leiningen. I'm also using tools.namespace to reload Clojure code while running a REPL. If I want to include Java source in the project, can I recompile and reload it while the REPL is running? What is the most convenient/dynamic way of doing it? Can I do it so that it works well with tools.namespace?

Answer 1

I'm answering my own bounty here but I did do a bit of work getting this up:

Use Vinyasa,

and here is a blog post:

Dynamic reloading of java code in emacs/nrepl

... actually... it's kinda not working anymore... you have to do back to the earlier versions in order to get the support.

Answer 2

Nowadays (2016->) the better answer is to use Virgil. It watches and recompiles all Java code in your leiningen project automatically in the background, as opposed to Vinyasa's approach of invoking reimport.

Answer 3

Spring-loaded or JRebel might be what you want. Have a look at https://github.com/spring-projects/Spring-loaded or http://zeroturnaround.com/software/jrebel/. They both provide an agent monitoring the filesystem for class file changes and update class definitions in the running JVM. I personally use Spring-loaded, but not yet together with tools.namespace. I guess the key to run them both is to make sure they do not conflict. So if you use Spring-loaded, it should be the only tool tracking class files and you better not use aot at all. If I remember correctly, tools.namespace discourages the use of aot anyways.

Answer 4

Pure java way

public class MyClassFactory {
   public static MyClass newInstance() {
       URLClassLoader cl =
           new URLClassLoader(new URL[] {getMyClassPath()}) {

           public Class loadClass(String name) {
              if ("MyClass".equals(name))
                 return findClass(name);
              return super.loadClass(name);
          }
       };

     return (MyClass) cl.loadClass("MyClass").newInstance();
  }
}

by this way you can lead the class loader to load classes programmatically.

References

• Classloader Official documentation
• Java Specs
• OnJava

Answer 5

See also the official JVM services loader

ServiceLoader