private void configureLogbackExternal(Bundle bundle) throws JoranException, IOException {
	    LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();
	    JoranConfigurator jc = new JoranConfigurator();
	    jc.setContext(context);
	    context.reset();

	    // overriding the log directory property programmatically
//	    String logDirProperty = "";// ... get alternative log directory location
//	    context.putProperty("LOG_DIR", logDirProperty);

	    // get the configuration location where the logback.xml is located
	    Location configurationLocation = Platform.getInstallLocation();
	    File logbackFile = new File(configurationLocation.getURL().getPath(), "logback.xml");
	    if(logbackFile.exists()) {
	        jc.doConfigure(logbackFile);
	    } else {
	        URL logbackConfigFileUrl = FileLocator.find(bundle, new Path("logback.xml"), null);
	        jc.doConfigure(logbackConfigFileUrl.openStream());
	    }
	}	

Root exception:
org.eclipse.core.runtime.AssertionFailedException: assertion failed: The application has not been initialized.
	at org.eclipse.core.runtime.Assert.isTrue(Assert.java:110)
	at org.eclipse.core.internal.runtime.InternalPlatform.assertInitialized(InternalPlatform.java:174)
	at org.eclipse.core.internal.runtime.InternalPlatform.getInstallLocation(InternalPlatform.java:340)
	at org.eclipse.core.runtime.Platform.getInstallLocation(Platform.java:1326)
	at config.Activator.configureLogbackExternal(Activator.java:101)
	at config.Activator.start(Activator.java:44)