Swing Hacks

Stuff Stuff in JARs #85

Chapter 11, Native Integration and Packaging

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HACK

An Obvious Secret

JAR files—the acronym is short for Java ARchive—must be the best-known,

least-used feature in Java. Many developers throw a JAR in their classpath to

pick up some standard extension API or third-party library, but how many

actually distribute their software that way?

And JARs aren’t just about code. It’s really easy to put the files your pro-

gram needs into a JAR. This has the added advantage of hiding your images,

sounds, default settings, and so forth from end users.

But to load these items, you need to make a change in how you load stuff in

your code. Instead of specifying a known path or URL, you ask a

ClassLoader to find these resources along the classpath. By doing this, you

can get your resources from flat files while you’re developing, and then eas-

ily switch to getting them from inside a JAR when the code is deployed in

the field.

The key is the

ClassLoader’s getResource( ) and getResources( ) methods,

which take a path relative to the loaded class and return a

URL and an array

of

URLs respectively. A getResourceAsStream( ) method converts the URL to an

InputStream as a convenience.

To clarify the relative path: say you have a directory that includes your com-

piled classes in a path like com/mycompany/mypackage/…, an images direc-

tory, and a sounds directory. A relative path would be one of the ...