Offline running - can "GetResources() for an embedded file ever work?

Question

This question has come up in various guises in the past, but has often then become confused with other issues (see [t-5123126] ) so I've not been able to find a useful answer. I've tried to bring the problem down to the essentials, and just want to know if what I'm trying to do can ever work, or if I should just abandon Web Start for this particular need.
Our app is J2SE Swing and creates a Derby database locally on a PC. The application then captures keyed data and stores it on the local database. Persistence is via JPA (provider was Toplink, now EclipseLink).
The data capture is performed using laptops running the application "offline" with no network connection. This is because the location has no network access of any description. Periodically, each laptop is reconnected to upload its data to a central server.
To help with software distribution, we are using Java Web Start. All the jars are signed and the .jnlp file specifes offline usage is allowed.
When running the application while connected to the network, there are no issues - everything works fine.
When running offline, the application starts up so the Java Web Start caching is working and the code is obviously accessible. However, it throws a MalformedURLException within the EclipseLink code (which we do not wish to modify). The actual statement is:
Enumeration resources = classLoader.getResources("META-INF/persistence.xml"); META-INF/persistence.xml exists within one of the jar files specified as resources in the .jnlp file.
The classloader in question is the Java Web Start classloader ( com.sun.jnlp.JNLPClassLoader) which presumably retrieves classes and resources from the remote server or from the cache depending on how the app is being run. In online mode, the persistence.xml resource is found ok, in offline a MalformedURLException is thrown.
My question: is this a fundamental "restriction" of the Web Start environment in offline mode? i.e. it can't load resources such as this xml file from a cached jar using the format shown?. My feeling is that this is just the way it is, and I should move on and try another form of software distribution, but it seems a shame to abandon Web Start as it otherwise meets our needs.
Any relevent experience of this problem would be appreciated.
Edited by: GrayMan on Aug 21, 2009 8:20 AM

Answer 1

A system we're developing make use of a similar setup. I'm not sure if you run into this problem, but the classes in our app uses persistence annotations and do not rely on the orm.xml mapping file. After solving the persistence.xml show stopper, I could see that the application had really slow startup times in offline mode. By looking at the access logs in online mode, I could see that the app was requesting META-INF/orm.xml and META-INF/eclipselink-orm.xml. In online mode, the web server simply returned HTTP 404 with much delay. In offline mode, this resulted in really slow startup times due to timeouts for the mentioned requests.
Creating valid xml files bundling them into the jar file of course didn't help.
I successfully disabled lookup for eclipselink-orm.xml by specifying the following entry in persistence.xml:
<property name="eclipselink.exclude-eclipselink-orm" value="true"/>
To disable lookup for orm.xml, I modified the method loadStandardMappingFiles(String) in org.eclipse.persistence.internal.jpa.metadata.MetadataProcessor.MetadataProcessor (eclipselink 1.1.0).
Perhaps this is useful for someone else also.