Re: resources from JAR files

Lew <>
Fri, 25 Jan 2013 22:32:03 -0800 (PST)
Arne Vajh=F8j wrote:

BGB wrote:

it can also be noted that it does matter which class you pick, like

That's partly correct, as five minutes' reading of the 'getResource()' meth=
od docs will
reveal. What actually matters is what classloader you pick; any number of c=
lasses (and
frequently all the ones you have access to) are loaded by one classloader.

As for the seeming arbitrariness of the idiom that started this thread, per=
haps the
programmer picked a class known to have the correct classloader, is all.

generally you want the class and resource file to be in the same package

That's not true.

and JAR and similar (the class basically telling the JVM where to look,

That's not true either, and that's not true.

You can have the resource in any package that makes sense. Common conventio=
are 'resource', 'resources', 'res', or those relative to the "official" pac=
kage root of your
application, such as 'com.lewscanon.slicedbread.resources'.

And as stated, it's "basically" the classloader telling the JVM where to lo=

otherwise the resource may not be found).

The resource will be found if it's in the location specified by the argumen=
t to the call.

That can be the default package, the same package, a different package, or =

Same JAR, different JAR, remote URL, whatever.

so, while a person can pick an arbitrary class, it may not necessarily
find the resource.

You should never pick an arbitrary class, however you may pick an arbitrary=
class from the set of those that use the appropriate classloader, or even u=
the classloader directly. It's all good. If you read the Javadocs, you will=
 not guess
but know that the call is correct.

so, generally, picking 'this' or similar makes sense, since normally a

Because generally you want the same classloader as the caller's.

What is "or similar"?

person will package the resources along with their own code.

Normally by what metric?

You put the resources where the architecture of the system mandates. Again,=
that can be remote - quite common for applets in their day - from a JAR,
from anywhere accessible to a classloader. You are correct to the extent th=
the default classloader is often the one you want, so 'this' or 'Type.class=
' do just
fine. But that's an arbitrary choice.

or such...

False analogy.

I would use "the class" of this, so ...
And the class method can be used in static context.

Note: He means "method" in the English sense here, as in "means of getting =
to the classloader",
not as in "the class literal is a Java method".

Bear in mind that the 'Class' version of 'getResource()' is a convenience m=
ethod - the
'ClassLoader' version is the workhorse.

Don't use these calls by rule of thumb as BGB suggests. Breaking into 'Clas=
s' methods and more so
'ClassLoader' methods is of the world of reflection, and classpaths, and pa=
connections, and stuff that that breaks type safety. This is part of the he=
art of what makes Java Java.
This is stuff you need to actually know, not do by cargo-cult programming.


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