Using SWT with Java Web Start on Mac OSX

Developing rich-client applications has several usability advantages over web applications, but many times recurring deployment costs inhibit us from using rich-client applications in an enterprise environment where IT is responsible for all software installations and upgrades. Java Web Start provides an elegant way to automatically deploy and update rich-client applications without the costs associated with traditional deployments. SWT provides a great toolkit that makes Java applications appear very native and enhance usability dramatically. However, because of a bug in the Mac OSX implementation of SWT, you cannot launch SWT via the standard Java Web Start client that comes packaged with the operating system. After looking around for a solution to work around this bug, I've come up with the following. Note that this approach is not ideal, but it will let you deploy SWT applications using Java Web Start on Mac OSX.

Using a Different JNLP Client

The normal Web Start client that comes with OSX is a Swing based client, which causes all sorts of problems when trying to launch SWT applications since those applications are launched in the same process. In order to get around this, we needed a Web Start launcher that did not contain a front end. To this end, we employed OpenJNLP, an open implementation of the Java Web Start standard. We were able to de-activate the Swing frontend and just use the client's dpwnloading, caching, and launching facilities.

Bundling the Launcher Into a Nice Package

After writing a shell script to launch our SWT Web Start applications, we then created a small application bundle that serves as the launcher. So, in order to deploy this, the user just needs to download this application bundle once, and when the bundle is run, it will download the application resources, launch the application, and keep the resources up to date - all behind the scenes.

Here's a sample of our application bundle: jnlp_launcher.dmg

You will notice that this bundle is little more than a few OpenJNLP jars and a shell script to launch the client. To set the URL of the Web Start repository that you want to launch from, right-click on the bundle and choose "Show Package Contents". Browse to the "Contents/MacOSX" folder. Inside you will find a file called "jnlplaunch". This is the launcher shell script. Edit the script and insert your URL after JNLPURL=. Save it and the launcher should be ready to use.

#!/bin/sh
JNLPURL=http://moria/jaguar/webstart/production/jaguar-macosx-moria.jnlp
BASEDIR=`dirname "$0"`
CP=../MacOS
cd "$BASEDIR/../WorkDir"
java \
	-XstartOnFirstThread \
	-classpath $CP/jnlp.jar:$CP/openjnlp-app.jar:$CP/openjnlp-lib.jar:$CP/openjnlp-extra.jar \
	-Dorg.eclipse.swt.internal.carbon.noFocusRing \
	-Dorg.eclipse.swt.internal.carbon.smallFonts \
	org.nanode.jnlp.JNLPParser -internal $JNLPURL

Gotchas

There are several problems with this solution. First is that the OpenJNLP project seems to be dying. At least they didn't return my e-mails and progess seems to have halted. However, their code is still quite usable, but isn't terribly complete.

Also, the OpenJNLP client does not seem to implement extensions in the JNLP file. So, if you are using those, you will have to rewrite the JNLP file without extensions.

Most of the time extensions are used to separate jar files that are signed by different authorities. However, OpenJNLP does not implement any security measures, so signing jar files is not necessary and therefore extensions do not need to be used for that.

The other major problem is that the user has no way of knowing what is happening when they launch the launcher. It just bounces in the dock until all resources are downloaded and up to date. Depending on the size of application and the network, this could take a while. An enhancement to this shell script would be to pop up a dialog box explaining what is happening in the background.

Conclusion

All in all, this is definitely not a long-term solution. It would be much nicer to use the Web Start client that comes with Mac OSX, but this will hopefully allow you to deploy SWT applications across an enterprise environments without having to build and distribute application bundles for Mac OSX for each update.

Author
Written by Nathan Callender
Application Developer
November 9, 2005

Related Sources
OpenJNLP Home Page

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