org.ontoware.rdf2go.osgi.RDF2GoActivator Maven / Gradle / Ivy

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RDF2go is an implementation-independent Java API with the design goals: portability (hence the name), performance and ease of implementation. This project was started at FZI Forschungszentrum Informatik Karlsruhe, Germany - www.fzi.de
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/**
 * LICENSE INFORMATION
 * 
 * Copyright 2005-2008 by FZI (http://www.fzi.de). Licensed under a BSD license
 * (http://www.opensource.org/licenses/bsd-license.php)  = Max Völkel
 *  = FZI Forschungszentrum Informatik Karlsruhe, Karlsruhe,
 * Germany  = 2010
 * 
 * Further project information at http://semanticweb.org/wiki/RDF2Go
 */

package org.ontoware.rdf2go.osgi;

import org.ontoware.rdf2go.ModelFactory;
import org.ontoware.rdf2go.RDF2Go;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.InvalidSyntaxException;
import org.osgi.framework.ServiceEvent;
import org.osgi.framework.ServiceListener;
import org.osgi.framework.ServiceReference;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * Activate the RDF2Go framework. Listens to registered OSGI services and
 * searches for registered {@link ModelFactory} instances. The found factories
 * are compared to a configuration value, if the configured factory is found, it
 * is set as default. This is the configuration value to set:
 * org.ontoware.rdf2go.defaultmodelfactory=(classname of modelfactory)
 * 
 * This class has been contributed by Deutsches Forschungszentrum fuer
 * Kuenstliche Intelligenz DFKI GmbH.
 * 
 * TODO sauermann why cannot just the implementation bundle register itself? It
 * shouldn't be the APIs job to register implementations.
 * 
 * @author sauermann
 */
public class RDF2GoActivator implements BundleActivator, ServiceListener {
	
	/**
	 * set this variable in the OSGI config to define the default driver for
	 * RDF2Go.
	 */
	public static final String DEFAULTMODELFACTORY_CFG = "org.ontoware.rdf2go.defaultmodelfactory";
	
	/**
	 * The filter used to search for ModelFactories
	 */
	public static final String MODEL_FACTORY_FILTER = "(objectclass="
	        + ModelFactory.class.getName() + ")";
	
	private BundleContext bc;
	
	private String defaultFactoryClassName = null;
	
	private ServiceReference currentFactorySR;
	
	private static final Logger log = LoggerFactory.getLogger(RDF2GoActivator.class);
	
	/**
	 * @see org.osgi.framework.BundleActivator#start(org.osgi.framework.BundleContext)
	 */
	@Override
	public void start(BundleContext context) throws Exception {
		this.bc = context;
		this.defaultFactoryClassName = context.getProperty(DEFAULTMODELFACTORY_CFG);
		this.bc.addServiceListener(this, MODEL_FACTORY_FILTER);
		initalizeListener();
	}
	
	private void initalizeListener() {
		ServiceReference references[];
		try {
			references = this.bc.getServiceReferences((String)null, MODEL_FACTORY_FILTER);
			for(int i = 0; references != null && i < references.length; i++) {
				this.serviceChanged(new ServiceEvent(ServiceEvent.REGISTERED, references[i]));
			}
		} catch(InvalidSyntaxException e) {
			// this will not happen
			log.error("Syntax error", e);
		}
	}
	
	/**
	 * @see org.osgi.framework.BundleActivator#stop(org.osgi.framework.BundleContext)
	 * 
	 *      TODO leo/antoni document why context is not needed/used for stopping
	 *      the bundle
	 */
	@Override
	public void stop(BundleContext context) throws Exception {
		this.bc = null;
	}
	
	/**
	 * Listen to changes in the ModelFactories.
	 * 
	 * @see org.osgi.framework.ServiceListener#serviceChanged(org.osgi.framework.ServiceEvent)
	 */
	@Override
	public void serviceChanged(ServiceEvent event) {
		switch(event.getType()) {
		case ServiceEvent.REGISTERED:
			handleRegisteredEvent(event);
			break;
		case ServiceEvent.UNREGISTERING:
			handleUnregisteredEvent(event);
			break;
		}
		// We do not care for modified
		// case ServiceEvent.MODIFIED:
	}
	
	private void handleRegisteredEvent(ServiceEvent event) {
		ServiceReference ref = event.getServiceReference();
		ModelFactory factory = (ModelFactory)this.bc.getService(ref);
		String currClass = getCurrentFactoryClassName();
		String newClass = factory.getClass().getName();
		if(this.currentFactorySR == null) {
			log.debug("Registering " + factory.getClass().getName() + " as default ModelFactory");
			this.currentFactorySR = ref;
			RDF2Go.register(factory);
		} else if(this.defaultFactoryClassName != null
		        && !currClass.equals(this.defaultFactoryClassName)
		        && newClass.equals(this.defaultFactoryClassName)) {
			RDF2Go.register((ModelFactory)null);
			this.bc.ungetService(this.currentFactorySR);
			
			factory = (ModelFactory)this.bc.getService(ref);
			this.currentFactorySR = ref;
			RDF2Go.register(factory);
			log.debug("RDF2Go uses " + newClass + " as default ModelFactory");
		} else {
			this.bc.ungetService(ref);
		}
	}
	
	private void handleUnregisteredEvent(ServiceEvent event) {
		ServiceReference ref = event.getServiceReference();
		String currClass = getCurrentFactoryClassName();
		if(ref == this.currentFactorySR) {
			RDF2Go.register((ModelFactory)null);
			this.currentFactorySR = null;
			log.debug("RDF2Go unregistered the ModelFactory " + currClass
			        + " as default ModelFactory. No ModelFactory available now. "
			        + "The Bundle of the ModelFactory was unregistered.");
		}
		this.bc.ungetService(ref);
		initalizeListener();
	}
	
	private static String getCurrentFactoryClassName() {
		ModelFactory currFactory = null;
		try {
			currFactory = RDF2Go.getModelFactory();
		} catch(RuntimeException e) {
			// do nothing, this means that no factory has been registered
		}
		return (currFactory == null ? null : currFactory.getClass().getName());
	}
}