In some cases, “lein repl” will fail with “java.lang.ClassNotFoundException: org.codehaus.jackson.JsonFactory”. I have solved this problem, at least for my project. Read here why.

As I wrote before, I am currently learning clojure, and so I implement a simple web applicatoin. I build and run this application using Leiningen. There I encountered a problem: When I run

> lein clean
> lein run

…and then try to launch a repl, it fails with

> lein repl
Compiling newsreader.server
Exception in thread "main" java.lang.ExceptionInInitializerError, compiling:(clutch.clj:1)
        ... A very long stack trace ...
Caused by: java.lang.ClassNotFoundException: org.codehaus.jackson.JsonFactory
        at$ Source)
        ... more stack trace elements ...

This seems to be caused by a known problem in leinignen. Anyway, I want to run the server AND the REPL. I recognized that, when I run

> lein clean
> lein repl

the REPL will work fine, but the server won’t start anymore. The solution - at least in my case - is quite simple: Start the server from the REPL:

> lein repl
Compiling newsreader.server
    ... more output from the REPL ...
newsreader.server=> (-main)
Starting server...
2012-11-14 09:44:25.918:INFO::Logging to STDERR via org.mortbay.log.StdErrLog
Server started on port [8080].
You can view the site at http://localhost:8080
#<Server Server@f6dd4>
newsreader.server=> 2012-11-14 09:44:25.919:INFO::jetty-6.1.25
2012-11-14 09:44:25.938:INFO::Started SocketConnector@

newsreader.server=> (+ 2 3)

And this works really well for me. Now, if only SublimeREPL would already work with leiningen2…

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