Using custom Java classes in Clojure REPL

问题

In Eclipse, using the CCW plug-in, I want to load a clojure file into a REPL. The problem is that I have an import statement for one of my own java classes, but apparently it is not in my classpath.

(ns my-clj-ns
  (:import [alg.gen Enumerator]))

Do I have to make jars out of every class that I want use/test in a Clojure REPL?

Currently, trying to load my clj into a REPL results in an error: "Load file in Clojure REPL" did not complete normally. Please see the log for more information. java.lang.NullPointerException

Any help would be greatly appreciated.

回答1:

Your code looks fine to me.

I suspect the issue is with your Eclipse Java Build Path, which determines what Eclipse includes in the classpath for your application.

In particular, if your Java class is in a separate project, you will need to either add that project to the build path (right click on project / Properties / Java Build Path / Projects) or package it as a jar.

When you start to have more sophisticated build requirements, you may also want to start looking at Maven to handle this kind of thing for you. Maven is a pain to learn / set up in the first place but it pays of in the long run.

Leiningen is also a great tool to use but I personally don't use it for the following reasons:

It is great on the command line, but doesn't integrate so nicely with an Eclipse workflow
Maven is more widely used and better supported in the Java world

回答2:

You can let leiningen compile these for you using,

:javac-options {:destdir "classes/"}
:java-source-path "src/main/java" ; location of Java source

options or manually compile them and move the class files to the classes/ directory. No need to create a jar.

回答3:

When you're in the ccw repl, you can hit alt-e to see the stack trace. If you're getting a NullPointerException, I don't think its a classpath issue.

回答4:

There is really nice guide if you want to learn how to do this.

https://github.com/technomancy/leiningen/blob/master/doc/MIXED_PROJECTS.md

But in gist, have a project definition like the following for Java source code.

(defproject megacorp/superservice "1.0.0-SNAPSHOT"
  :description "A Clojure project with a little bit of Java sprinkled here and there"
  :source-paths      ["src/clojure"]
  :java-source-paths ["src/java"])

来源：https://stackoverflow.com/questions/8401533/using-custom-java-classes-in-clojure-repl

标签

java

clojure

classpath