raghusauce / mixing-java-and-clojure Goto Github PK

## Description

This is a simple demonstration of 

   1) Java interop, and
   2) build management using the new capabilities of Leiningen.

This "project" came about from a conversation with a colleague about how to maintain two sets of code, one in Java and the other in Clojure, and be able to easily build an app using them.

## Building

You need a newer version of Leiningen which has the javac task available to it. You can get it here: https://github.com/technomancy/leiningen. I believe this task was added in 1.4.0, but you should simply use the latest version, which at this time is 1.5.2.

Once you have that set up, simply open up a command prompt at the project and run the following:

    lein uberjar
    java -jar mixing-java-and-clojure-1.0.0-SNAPSHOT-standalone.jar

You should see the following echoed to the screen:

    I am in Foo.java!!!
    I am in bar.clj!!!

In order for this to work in your project, namely being able to call Java code from within Clojure and be able to compile it all easily, you have to define the project correctly in project.clj. Here is the configuration for this simple project:

    (defproject mixing-java-and-clojure "1.0.0-SNAPSHOT"
      :description "A simple demonstration of Java interop and build management using javac"
      :dependencies [[org.clojure/clojure "1.2.0"]
                     [org.clojure/clojure-contrib "1.2.0"]]
      :source-path "src/clojure"
      :java-source-path "src/java"
      :main com.quephird.mjac.bar)

The key key (no pun intended) here is :java-source-path. If you leave it out, lein uberjar (or lein javac) will fail with something like this:

E:\foo>lein uberjar
Cleaning up.
Copying 2 files to E:\foo\lib
Exception in thread "main" java.lang.ClassNotFoundException: com.quephird.mjac.F
oo (bar.clj:1)
        at clojure.lang.Compiler$InvokeExpr.eval(Compiler.java:2911)
        at clojure.lang.Compiler.compile1(Compiler.java:5933)
        at clojure.lang.Compiler.compile1(Compiler.java:5923)
        at clojure.lang.Compiler.compile(Compiler.java:5992)
        at clojure.lang.RT.compile(RT.java:368)
        at clojure.lang.RT.load(RT.java:407)
        at clojure.lang.RT.load(RT.java:381)
        at clojure.core$load$fn__4511.invoke(core.clj:4905)
        at clojure.core$load.doInvoke(core.clj:4904)
        at clojure.lang.RestFn.invoke(RestFn.java:409)
        at clojure.core$load_one.invoke(core.clj:4729)
        at clojure.core$compile$fn__4516.invoke(core.clj:4916)
        at clojure.core$compile.invoke(core.clj:4915)
        at user$eval7.invoke(NO_SOURCE_FILE:1)
        at clojure.lang.Compiler.eval(Compiler.java:5424)
        at clojure.lang.Compiler.eval(Compiler.java:5415)
        at clojure.lang.Compiler.eval(Compiler.java:5391)
        at clojure.core$eval.invoke(core.clj:2382)
        at clojure.main$eval_opt.invoke(main.clj:235)
        at clojure.main$initialize.invoke(main.clj:254)
        at clojure.main$null_opt.invoke(main.clj:279)
        at clojure.main$main.doInvoke(main.clj:354)
        at clojure.lang.RestFn.invoke(RestFn.java:422)
        at clojure.lang.Var.invoke(Var.java:369)
        at clojure.lang.AFn.applyToHelper(AFn.java:165)
        at clojure.lang.Var.applyTo(Var.java:482)
        at clojure.main.main(main.java:37)
Caused by: java.lang.ClassNotFoundException: com.quephird.mjac.Foo
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at clojure.lang.DynamicClassLoader.findClass(DynamicClassLoader.java:58)


## License

Copyright (C) 2011, dan kefford
Distributed under the Eclipse Public License, the same as Clojure.