Menu
Here I check the environment variable CLASSPATH
daniel@daniel-laptop:~/ps/clojure/projects/ring-tutorial$ echo $CLASSPATH
/home/daniel/ps/clojure/projects/ring-tutorial/src
Here I check what java thinks it is.
daniel@daniel-laptop:~/ps/clojure/projects/ring-tutorial$ lein repl
Clojure 1.1.0
user=> (System/getProperty "java.class.path")
"src/:classes/:/home/daniel/.m2/repository/leiningen/leiningen/1.1.0/leiningen-1.1.0-standalone.jar:lib/clojure-1.1.0.jar:lib/servlet-api-2.5-6.1.14.jar:lib/commons-io-1.4.jar:lib/clj-stacktrace-0.1.0.jar:lib/clojure-contrib-1.1.0.jar:lib/ring-devel-0.2.0.jar:lib/jetty-util-6.1.14.jar:lib/clj-html-0.1.0.jar:lib/ring-jetty-adapter-0.2.0.jar:lib/jetty-6.1.14.jar:lib/ring-core-0.2.0.jar:lib/commons-fileupload-1.2.1.jar:lib/ring-servlet-0.2.0.jar:lib/commons-codec-1.4.jar:"
As you can see, the two responses are completely different. I'm pretty sure that I must just be misunderstanding where I ought to be editing the CLASSPATH variable for java to "get it," except that everything I've found says that this should work. So what's the deal? Does leiningen spawn its own weird renegade instance of clojure? Am I editing a completely irrelevant variable? Any help much appreciated.
979
Classpath is an environment variable that is used by the application ClassLoader or system to locate and load the compiled Java bytecodes stored in the . class file. To set CLASSPATH. the CLASSPATH can be overridden by adding classpath in the manifest file and by using a command like set -classpath.
The main difference between PATH and CLASSPATH is that Path is set for java tools in java programs like java and javac, which are used to compile your code. Whereas CLASSPATH is used by System or Application class loader to locate and load compile Java bytecodes stored in the . class file.
To check our CLASSPATH on Windows we can open a command prompt and type echo %CLASSPATH%. To check it on a Mac you need to open a terminal and type echo $CLASSPATH.
$CLASSPATH is indeed completely irrelevant here. It is what java-the-JVM-launcher-programme would use if no classpath information was provided to it on the command line; Leiningen provides the JVM with a classpath appropriate to whichever project you're working on.
In this particular case, "/home/.../ring-tutorial/src" would not be a very useful classpath for the Ring tutorial, since it only includes the Ring tutorial's source and does not include the Clojure jar (which is necessary for running Clojure code), the Ring jars (Ring is a multi-module project) or any of the other jars Ring depends on. The classpath produced by Leiningen might seem pretty long, but all of its components really need to be there.
Incidentally, if you're just starting out with Clojure, I'd recommend you stick to your toolchain's classpath management facilities (that might mean Emacs + lein swank or some IDE + the Clojure plugin) if at all possible. Otherwise, there's a lot of questions on Clojure classpath issues here on SO, plus a multitude of other resources on the topic you can google for... but now that tool support is pretty robust and you don't normally need to touch classpath by hand, it's just pain best avoided in the beginning.
60
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
