[JAVA]Accessing build date/time at runtime

[JamesCherrill]

My app is a straightforward Java SE 6 program, built in Eclipse and distributed as a single executable jar (I don't need or use any advanced build tools such as ant).

I want to automate the process of getting accurate version information into the "About" message, because right now I have to remember to open the main class and update a version String every time I rebuild the app.

Ideally I'd like to automatically insert the date/time when the code (or the jar) was built into something I can access at runtime, but any workable approach would do.

Does anyone have any suggestions?

Thanks

James

[skyfox01_99]

Use an Ant task to generate a "Version" class at build time that contains the version value as a public static field. You can use that field to get the version information.

<property name="Version" value="1.1.0" />

<target name="build" depends="init">
	...

	<echo file="my/project/Version.java">lic class Version {
	public static final String VERSION = "${Version}";
}
	</echo>
</target>

You could use an Ant <script> task to fill the Version variable if you want something a bit more dynamic.

[JamesCherrill]

Hi skyfox - thanks for the reply. What I'm looking for is,as you say, "a bit more dynamic", ie something that will automatically make the build date/time available at runtime without the need to edit anything manually for each build. Ps - I've never worked with ant, so maybe the learning curve would be disporportionate to the problem being solved? What do you think?

[Mike]

If you have a script to compile it for you, how about having it create a Version class manually? Just a few simple echo statements to write out a simple class with a static method for getting the version/build time.

[JamesCherrill]

Hi Mike. No, I don't have a script. The app just has a couple of hundred classes, so it's easiest to just let Eclipse keep all the class files up to date (Project > Build Automatically)and then all I have to do is right-click the jar description to get a new jar exported.

[JamesCherrill]

OK guys, I found a hint that lead me to this

		try {
			File jarFile = new File
			(this.getClass().getProtectionDomain().getCodeSource().getLocation().toURI());
			System.out.println("jar: " + new Date(jarFile.lastModified()));
		} catch (URISyntaxException e1) {
		}

which gives me the last modified date for the jar that the class was loaded from. That's pretty good for what I need...

... unless anyone has a better idea?

Edited March 15, 2009 by JamesCherrill

[Mike]

I found this package's API, which suggest it returns the build date:

http://www.clapper.org/software/java/util/.../BuildInfo.html

More info on it here: http://www.clapper.org/software/java/util/

I took a peek at the source code to see how it got the build date but couldn't find it, it just seemed to store the current date in a property :/

[_kane81]

^^

I had that same idea James, however I suspect the date time stuff on the jar maybe o/s dependednt (so if you download of the net or switch to unix you may lose your timestamp)...

unless you can read the modified date time off a class inside the jar.... but then again not all class files are always rebuilt when exporting to a jar... or are they?

[JamesCherrill]

The app is tied in to other Windows services, so I don't need OS independence. With Eclipse automatic build, .java files are re-compiled only when necessary, so the .class file for any given class may be quite old. I haven't tried uploading/downloading it via the net, so maybe that's a problem - I know that just copying it via a shared folder on a server preserves the last modded date.