Using Jar Files and Java Webstart
You can create executable jar files that can be "run" or executed by
double-clicking the jar file. These also form the basis for code you can
launch via Java webstart.
You can create the jar file from within Eclipse (see below). But if the
code reads images or other files to work you'll have to refactor the
code so that it uses a URL-based location system to find resources
rather than a file-based resource system.
Opening Files/Images
For example, to open a file named "data.txt" in your code you
might use this code:
<![CDATA[
Scanner scan = new Scanner(new File("data.txt"));
// process using scan.hasNext() scan.next() and so on
]]>
That code works fine if "data.txt" is accessible from wherever
the Java code is running (e.g., your Eclipse folder). But that
code won't work when using an executable jar file. Instead you
need a URL to locate the file. The code below will work both
from within Eclipse/the command line and from a jar file.
<![CDATA[
Scanner scan =
new Scanner(this.getClass().getResourceAsStream("/data.txt"));
// process scan.hasNext() and scan.next()
]]>
The method getResourceAsStream from java.lang.Class
returns a stream from a URL. You can also get the URL and the
stream in separate steps (which is what
getResourceAsStream is doing underneath):
<![CDATA[
URL name = this.getClass.getResource("/data.txt");
InputStream is = name.openStream();
Scanner scan = new Scanner(is);
]]>
To read images from a file you do something very similar:
<![CDATA[
URL name = this.getClass.getResource("/image.jpg");
Image image = Toolkit.getDefaultToolkit().getImage(name);
]]>
You can read almost any resource using this technique, and it works both
from a jar file and from the file-system/Eclipse.
Executable Jar
From Eclipse select the project you want to jar-up, right click and
choose Export as shown below -- you can also choose
Export from the Ecllipse File-menu which yields the same
dialog (on the left below):
After choosing Export, select Java/jar file as shown in the
dialog on the right:
You'll have to choose a name for the jar file and you'll have to
specify the launch-point for the jar file as shown in this dialog
where you will Browse to locate the class with
public static void main you want.
Once you've created the executable jar file you can locate it and
double-click it to run. That should work fine if you've done the
URL-reading stuff shown above.
JNLP, Java web-start
Once you've created an executable jar file you can launch it from the
web via Java webstart. Use this
article as a start. If the webserver you're running from doesn't
associcate the right mime type with .jnlp files you'll be out-of-luck
for the casual user. But for the sophisticated user they can
download the .jnlp file and use javaws from the commandline:
javaws foobar.jnlp
