How to load program resources in Clojure
Solution 1
It's the directory structure.
Continuing with the scripting engine example in the OP, a Clojure equivalent would be:
(ns com.domain.example
(:gen-class)
(:import (java.io InputStreamReader))
(:import (javax.script ScriptEngineManager ScriptEngine)))
(defn load-resource
[name]
(let [rsc-name (str "com/domain/resources/" name)
thr (Thread/currentThread)
ldr (.getContextClassLoader thr)]
(.getResourceAsStream ldr rsc-name)))
(defn markdown-to-html
[mkdn]
(let [manager (new ScriptEngineManager)
engine (.getEngineByName manager "js")
is (InputStreamReader. (load-resource "showdown.js"))
_ (.eval engine is)
cnv-arg (str "new Showdown.converter().makeHtml(\"" mkdn "\")")]
(.eval engine cnv-arg)))
(defn -main
[]
(println (markdown-to-html "plain, *emphasis*, **strong**")))
Note that the path to the resources is com/domain/resources
for this code as opposed to com/domain/scriptingtest/resources
in the Java version. In the clojure version, the source file, example.clj
is in com/domain
. In the Java version, the source file, Example.java
is in the com/domain/scriptingtest
package.
When setting up a project in my IDE, NetBeans, the Java project wizard asks for an enclosing package for the source. The Clojure plugin, enclojure, asks for a namespace, not a package. I had never noted that difference before. Hence the "off-by-one" error in the directory structure expected.
Solution 2
(clojure.java.io/resource "myscript.js")
Solution 3
you can also use clojure.lang.RT/baseLoader
(defn serve-public-resource [path]
(.getResourceAsStream (clojure.lang.RT/baseLoader) (str "public/" path)))
Solution 4
I placed the file in testpkg/test.txt (relative to current directory).
Code:
(def x 5)
(def nm "testpkg/test.txt")
(def thr (Thread/currentThread))
(def ldr (.getContextClassLoader thr))
(def strem (.getResourceAsStream ldr nm))
(def strem2 (ClassLoader/getSystemResource nm))
(. System/out (println "First Approach:"))
(. System/out (println strem))
(. System/out (println))
(. System/out (println))
(. System/out (println "Second Approach:"))
(. System/out (println strem2))
$ java -cp .\;clojure.jar clojure.main test.clj
First Approach: java.io.BufferedInputStream@1549f94
Second Approach: file:/C:/jsight/javadevtools/clojure-1.1.0/testpkg/test.txt
clartaq
Programming statistics, numerical analysis, applied mathematics, and desktop applications. Java, C/C++, Lisp, Clojure, FORTRAN, APL, Forth, Mathematica, MATLAB, ...
Updated on June 03, 2022Comments
-
clartaq about 2 years
How do you load program resources such as icons, strings, graphical elements, scripts, and so on in a Clojure program? I am using a project layout similar to that in many Java projects where there is a "resources" directory hanging off of a "source" directory. A jar file is created from the source and includes the resources, but I can't seem to get the resources loaded as I would in Java.
The first thing I tried was something like
(ClassLoader/getSystemResource "resources/myscript.js")
But could never find the resource.
You can do something similar with
... (let [cls (.getClass net.mydomain.somenamespace) strm (.getResourceAsStream cls name) ] ...
where name is the
name
of the resource to load, but the stream isnil
.You can try using the context class loader with something like
... (let [thr (Thread/currentThread) ldr (.getContextClassLoader thr) strem (.getResourceAsStream ldr name)] ...
But
strem
is always nil.In frustration, I've tried placing the resource files in just about every directory in the program. They get copied into the jar correctly, but I still can't seem to load them.
I've looked at the language sources for the
load
function and the run-time library, but am not "getting" it.Any help would be appreciated.
EDIT: Here's a more concrete example. In Java, if you wanted to convert MarkDown to HTML, you might use the
showdown.js
script and write something like:package scriptingtest; import java.io.InputStreamReader; import javax.script.Invocable; import javax.script.ScriptEngine; import javax.script.ScriptEngineManager; public class Example { private Object converter; public String transformMarkDown(String markdownString) { ScriptEngineManager manager = new ScriptEngineManager(); ScriptEngine engine = manager.getEngineByName("js"); try { engine.eval(new InputStreamReader(getClass().getResourceAsStream( "resources/showdown.js"))); converter = engine.eval("new Showdown.converter()"); } catch (Exception e) { return "Failed to create converter"; } try { return ((Invocable) engine).invokeMethod(converter, "makeHtml", markdownString).toString(); } catch (Exception e) { return "Conversion failed"; } } public static void main(String[] args) { System.out.println(new Example().transformMarkDown("plain, *emphasis*, **strong**")); } }
when I create the project, it all gets compiled and packed into a jar. When run, the program outputs
<p>plain, <em>emphasis</em>, <strong>strong</strong></p>
A literal translation to Clojure seems pretty straightforward, but I run into trouble trying to create the
InputStreamReader
-- I can't seem to write the code needed to find the script file in the jar.Edit: Added "markdown" tag since the post gives two complete examples of approaches to processing markdown.