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Swing Hacks by Chris Adamson, Joshua Marinacci

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Stuff Stuff in JARs #85
Chapter 11, Native Integration and Packaging
|
429
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 form
images/something.png, sounds/something.aiff, etc. By using a resource on the
classpath, there is no difference (to the user) between files in a JAR and files
in sub-directories on a filesystem. Either way, you get a
URL that you can use
by passing it to methods that take
URL arguments, by opening an
InputStream from it, etc.
Showing Off
Example 11-7 shows an example of this technique. It uses the getResource( )
method to load an image and put it in an ImageIcon, which in turn is used to
create a
JButton. It also loads in a sound, which is played via JavaSound
when you click the button.
Example 11-7. Loading image and sound as resources along the classpath
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.sound.sampled.*;
import java.net.*;
430
|
Chapter 11, Native Integration and Packaging
#85 Stuff Stuff in JARs
HACK
public class JarResourceLoading extends JFrame
implements ActionListener {
JButton button;
ImageIcon buttonIcon;
Clip buhClip;
public final static String SOUND_PATH = "sounds/buhbuhbuh.aiff";
public final static String IMAGE_PATH = "images/keagan-buh.jpeg";
public JarResourceLoading ( ) {
super ("Resources from .jar");
// get image and make button
URL imageURL = getClass().getClassLoader( ).getResource (IMAGE_PATH);
System.out.println ("found image at " + imageURL);
buttonIcon = new ImageIcon (imageURL);
button = new JButton ("Click to Buh!", buttonIcon);
button.setHorizontalTextPosition (SwingConstants.CENTER);
button.setVerticalTextPosition (SwingConstants.BOTTOM);
button.addActionListener (this);
getContentPane( ).add (button);
// load sound into Clip
try {
URL soundURL = getClass().getClassLoader( ).getResource (SOUND_PATH);
System.out.println ("found sound at " + soundURL);
Line.Info linfo = new Line.Info (Clip.class);
Line line = AudioSystem.getLine (linfo);
buhClip = (Clip) line;
AudioInputStream ais = AudioSystem.getAudioInputStream(soundURL);
buhClip.open(ais);
} catch (Exception e) {
e.printStackTrace( );
}
}
public void actionPerformed (ActionEvent e) {
System.out.println ("click!");
if (buhClip != null) {
buhClip.setFramePosition (0);
buhClip.start( );
}
else
JOptionPane.showMessageDialog (this,
"Couldn't load sound",
"Error",
JOptionPane.ERROR_MESSAGE);
}
public static final void main (String[] args) {
JFrame frame = new JarResourceLoading( );
Example 11-7. Loading image and sound as resources along the classpath (continued)
Stuff Stuff in JARs #85
Chapter 11, Native Integration and Packaging
|
431
HACK
Notice how the paths to the sound and the image are relative:
public final static String SOUND_PATH = "sounds/buhbuhbuh.aiff";
These paths specify the path from a given starting point. As
getResource( )
checks each entry in its classpath—whether they’re directories or JAR files
(ZIP files are also allowed)—the class loader looks for a directory called
sounds and, if that’s found, for an entry inside it called buhbuhbuh.aiff. It’s
also worth noting that you use the Unix-style forward slashes, regardless of
what operating system this is run on.
When you compile and run this code from the source directory, the result
looks like Figure 11-10.
Along with showing this simple GUI, it also prints to standard out the URLs
returned by
getResource( ). Running from the source directory, the output
looks like this:
[tonberry:] cadamson% java JarResourceLoading
found image at file:/Users/cadamson/Documents/O'Reilly/books/swing%20hacks/
HacksBook/PackagingInstalling/97/images/keagan-buh.jpeg
found sound at file:/Users/cadamson/Documents/O'Reilly/books/swing%20hacks/
HacksBook/PackagingInstalling/97/sounds/buhbuhbuh.aiff
frame.pack( );
frame.setVisible(true);
}
}
Figure 11-10. Application using image and sound loaded with getResource( )
Example 11-7. Loading image and sound as resources along the classpath (continued)

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