uk.org.retep.xmpp.jaxb.XMPPUnmarshaller Maven / Gradle / Ivy

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/*
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 * and open the template in the editor.
 */
package uk.org.retep.xmpp.jaxb;

import java.util.Collection;
import net.jcip.annotations.ThreadSafe;
import uk.org.retep.util.services.Service;
import uk.org.retep.util.xml.JAXBUtil;
import uk.org.retep.xmpp.annotation.XMPPProtocol;

/**
 * A singleton instance of {@link JAXBUtil} which contains the standard XMPP
 * packages.
 *
 * 
 *  When unmarshalling xmpp messages, this instance should be used as it would be
 *  unknown when a packet is received to what packages should be used.
 * 
 *
 * 
 *  When additional non-standard xmpp protocols are in use then they should be
 *  included in this instance prior to use.
 * 
 *
 * 
 *  When marshalling xmpp messages then XMPPMarshaller should be used as it
 *  will manage the creation of the correct contexts ensuring that no additional
 *  cruft is included in the resultant xml.
 * 
 *
 * @author peter
 */
@ThreadSafe
public class XMPPUnmarshaller
        extends JAXBUtil
{

    /**
     * The singleton instance
     * @return singleton
     */
    public static XMPPUnmarshaller getInstance()
    {
        return Holder.getInstance();
    }

    private XMPPUnmarshaller()
    {
        // Read the deployed packages and add them all to this instance.
        final Collection packages = Service.providerClassNames(
                XMPPProtocol.class.getName(),
                Thread.currentThread().getContextClassLoader() );

        for( String pkg : packages )
        {
            addPackage( pkg );
        }
    }

    /**
     * Holder pattern to lazy initialise the singleton as instantiation is
     * pretty expensive due to the number of packages involved.
     */
    private static class Holder
    {

        private static final XMPPUnmarshaller instance = new XMPPUnmarshaller();

        private Holder()
        {
        }

        static XMPPUnmarshaller getInstance()
        {
            return instance;
        }
    }
}