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resources from JAR files

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  resources from JAR files bob smith <bob@coolfone.comze.com> - 2013-01-17 08:30 -0800
    Re: resources from JAR files markspace <markspace@nospam.nospam> - 2013-01-17 08:54 -0800
    Re: resources from JAR files Roedy Green <see_website@mindprod.com.invalid> - 2013-01-17 15:07 -0800
      Re: resources from JAR files Lew <lewbloch@gmail.com> - 2013-01-17 15:16 -0800
        Re: resources from JAR files Roedy Green <see_website@mindprod.com.invalid> - 2013-01-17 16:36 -0800
          Re: resources from JAR files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-17 19:44 -0500
    Re: resources from JAR files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-17 18:13 -0500
      Re: resources from JAR files BGB <cr88192@hotmail.com> - 2013-01-25 15:08 -0600
        Re: resources from JAR files Arne Vajhøj <arne@vajhoej.dk> - 2013-01-25 20:57 -0500
          Re: resources from JAR files Lew <lewbloch@gmail.com> - 2013-01-25 22:32 -0800

#21478 — resources from JAR files

I have some code that reads an image from its JAR file like so:

img = ImageIO.read(frame.getClass().getResource("whatever.jpg"));

I basically just picked the "frame" object at random to call the getClass() method on it.

Is there a way to do this without picking an arbitrary object?  It seems so wrong.

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#21479

On 1/17/2013 8:30 AM, bob smith wrote:
> I have some code that reads an image from its JAR file like so:
>
> img = ImageIO.read(frame.getClass().getResource("whatever.jpg"));
>
> I basically just picked the "frame" object at random to call the getClass() method on it.
>
> Is there a way to do this without picking an arbitrary object?  It seems so wrong.
>


Yes, normally I use the object the line of code is contained it.

class MyBusinessObject {

   void someMethod() {
     Image img ImageIO.read( getClass().getResource( "whatever.jpg" ));
     // etc...
   }
}

You can also use a constant.  MyBusinessObject.class.getResource(...) 
instead of getClass().

You can also use 
Thread.currentThread().getContextClassLoader().getResource(...), but 
that's usually only useful in situations where thread contexts are used, 
i.e. web apps.

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#21498

On Thu, 17 Jan 2013 08:30:23 -0800 (PST), bob smith
<bob@coolfone.comze.com> wrote, quoted or indirectly quoted someone
who said :

>I have some code that reads an image from its JAR file like so:
>
>img = ImageIO.read(frame.getClass().getResource("whatever.jpg"));
>
>I basically just picked the "frame" object at random to call the getClass() method on it.
>
>Is there a way to do this without picking an arbitrary object?  It seems so wrong.

It is really just looking for a package name to find the resource. You
can name the main class explicitly  MyProg.class or this.getClass()
There is no Package class, so they use Class. You want something in
YOUR package.

see http://mindprod.com/jgloss/resource.html
-- 
Roedy Green Canadian Mind Products http://mindprod.com
The first 90% of the code accounts for the first 90% of the development time.
The remaining 10% of the code accounts for the other 90% of the development 
time. 
~ Tom Cargill  Ninety-ninety Law 

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#21501

Roedy Green wrote:
> There is no Package class, ...

http://docs.oracle.com/javase/7/docs/api/java/lang/Package.html

-- 
Lew

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#21504

On Thu, 17 Jan 2013 15:16:47 -0800 (PST), Lew <lewbloch@gmail.com>
wrote, quoted or indirectly quoted someone who said :

>Roedy Green wrote:
>> There is no Package class, ...
>
>http://docs.oracle.com/javase/7/docs/api/java/lang/Package.html

That came in 1.5, a fair bit after getResource. 
The one advantage of using class is it unambiguously specifies a jar,
even a jar whose name is unknown.
-- 
Roedy Green Canadian Mind Products http://mindprod.com
The first 90% of the code accounts for the first 90% of the development time.
The remaining 10% of the code accounts for the other 90% of the development 
time. 
~ Tom Cargill  Ninety-ninety Law 

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#21506

On 1/17/2013 7:36 PM, Roedy Green wrote:
> On Thu, 17 Jan 2013 15:16:47 -0800 (PST), Lew <lewbloch@gmail.com>
> wrote, quoted or indirectly quoted someone who said :
>
>> Roedy Green wrote:
>>> There is no Package class, ...
>>
>> http://docs.oracle.com/javase/7/docs/api/java/lang/Package.html
>
> That came in 1.5, a fair bit after getResource.

But 1.5 came out in 2004.

A fair bit of time ago.

Arne

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#21499

On 1/17/2013 11:30 AM, bob smith wrote:
> I have some code that reads an image from its JAR file like so:
>
> img = ImageIO.read(frame.getClass().getResource("whatever.jpg"));
>
> I basically just picked the "frame" object at random to call the getClass() method on it.
>
> Is there a way to do this without picking an arbitrary object?  It seems so wrong.

You need to pick either an object or a class.

I think it is relative common to pick either this or the class.

Arne

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#21715

On 1/17/2013 5:13 PM, Arne Vajhøj wrote:
> On 1/17/2013 11:30 AM, bob smith wrote:
>> I have some code that reads an image from its JAR file like so:
>>
>> img = ImageIO.read(frame.getClass().getResource("whatever.jpg"));
>>
>> I basically just picked the "frame" object at random to call the
>> getClass() method on it.
>>
>> Is there a way to do this without picking an arbitrary object?  It
>> seems so wrong.
>
> You need to pick either an object or a class.
>
> I think it is relative common to pick either this or the class.
>

FWIW, AFIAK:
it can also be noted that it does matter which class you pick, like 
generally you want the class and resource file to be in the same package 
and JAR and similar (the class basically telling the JVM where to look, 
otherwise the resource may not be found).

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

so, generally, picking 'this' or similar makes sense, since normally a 
person will package the resources along with their own code.


or such...

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#21716

On 1/25/2013 4:08 PM, BGB wrote:
> On 1/17/2013 5:13 PM, Arne Vajhøj wrote:
>> On 1/17/2013 11:30 AM, bob smith wrote:
>>> I have some code that reads an image from its JAR file like so:
>>>
>>> img = ImageIO.read(frame.getClass().getResource("whatever.jpg"));
>>>
>>> I basically just picked the "frame" object at random to call the
>>> getClass() method on it.
>>>
>>> Is there a way to do this without picking an arbitrary object?  It
>>> seems so wrong.
>>
>> You need to pick either an object or a class.
>>
>> I think it is relative common to pick either this or the class.
>>
>
> FWIW, AFIAK:
> it can also be noted that it does matter which class you pick, like
> generally you want the class and resource file to be in the same package
> and JAR and similar (the class basically telling the JVM where to look,
> otherwise the resource may not be found).
>
> so, while a person can pick an arbitrary class, it may not necessarily
> find the resource.
>
> so, generally, picking 'this' or similar makes sense, since normally a
> person will package the resources along with their own code.
>
>
> or such...

I would use "the class" of this, so ...

And the class method can be used in static context.

Arne

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#21724

Arne Vajhøj wrote:
> BGB wrote:
>> FWIW, AFIAK:
>> 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()' method docs will 
reveal. What actually matters is what classloader you pick; any number of classes (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, perhaps 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 conventions 
are 'resource', 'resources', 'res', or those relative to the "official" package root of your 
application, such as 'com.lewscanon.slicedbread.resources'.

And as stated, it's "basically" the classloader telling the JVM where to look.

>> otherwise the resource may not be found).

The resource will be found if it's in the location specified by the argument to the call.

That can be the default package, the same package, a different package, or whatever.

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 use 
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 that 
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 method - the 
'ClassLoader' version is the workhorse.

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

-- 
Lew

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