Classpath resources with Nashorn (JJS)

[Sundararajan Athijegannathan]

Rhino engine in jdk6 and jdk7 was loaded as bootstrap code. Nashorn is
loaded by extension class loader.

You can check Class.getResourceAsStream's javadoc:

https://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#getResourceAsStream%28java.lang.String%29

" If this object was loaded by the bootstrap class loader, the method
delegates to ClassLoader.getSystemResourceAsStream(java.lang.String). "

https://docs.oracle.com/javase/7/docs/api/java/lang/ClassLoader.html#getSystemResourceAsStream%28java.lang.String%29

"This method locates the resource through the system class loader (see
getSystemClassLoader())."

With Nashorn/jjs -classpath, you get new class loader (different from
system/launcher loader). And so calling
ClassLoader.getSystemResourceAsStream won't work either.

But, if you do load a class from your jjs -classpath path, then you can
get Class object of it and then call getResourceAsStream on it - like:

jjs -cp foo

jjs> var cl = com.acme.Foo.class; // assuming such as a class from path
"foo"

jjs> cl.getResourceAsStream("t.txt");

Also, you can use __DIR__ variable to load script relative files. The
directory in which your script is stored is available via __DIR__
variable. You can use that to load script relative resources.

Hope this helps,

-Sundar


On 9/26/2016 10:46 AM, Edgar Merino wrote:
> Hello:
>
>
>     I don't really know if this belongs here, I couldn't find much
> documentation on this issue.
>
>     I've noticed that, when using nashorn's command line utility JJS,
> any resource that is included in the classpath, be it included in a
> JAR or located in a classpath folder, is not available to scripts. A
> simple example:
>
> |echo "java.lang.Class.class.getResourceAsStream('/test.txt')"|jjs -cp .|
>
>     When a file "test.txt" is included in the current folder (which is
> added to the classpath via the -cp option), this code always returns
> "null". If I run a similar example using java and the jvm directly I
> get the expected resource (an input stream reference). Under rhino I
> get the same results, using a similar example.
>
>     Is this the expected behavior? Is there a way to access resources
> under the classpath in nashorn? This is causing a lot of problems with
> spring contexts for example, everytime I try to load my app context
> from an XML file I get problems because it cannot find some needed
> resources at runtime. This worked fine under rhino, but we are
> planning on migrating to nashorn.
>
> I found this github wiki, were it states loading resources is only
> possible for nashorn's app class loader:
> https://github.com/DaniHaag/snippets/wiki/Nashorn
> <https://github.com/DaniHaag/snippets/wiki/Nashornhttps://github.com/DaniHaag/snippets/wiki/Nashorn>
>
> This related question is given a useful answer, but it involves
> creating the nashorn engine programatically, instead of using JJS:
> http://stackoverflow.com/questions/30225398/java-8-scriptengine-across-classloaders
>
>
>
> Any help is greatly appreciated.
>
> Edgar Merino.
>