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Core Implementation of LD Path a simple path-based query language similar to XPath or SPARQL Property Paths that is particularly well-suited for querying and retrieving resources from the Linked Data Cloud by following RDF links between resources and servers.

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package at.newmedialab.ldpath.model.transformers;

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.Duration;

import at.newmedialab.ldpath.api.backend.RDFBackend;
import at.newmedialab.ldpath.api.transformers.NodeTransformer;

/**
 * Transforms (and validates) the lexical value of a node to
 * {@link Duration}.
 * @author Rupert Westenthaler
 * @param  the generic node type
 */
public class DurationTransformer implements NodeTransformer {

    /**
     * Lazy initialisation to avoid Exceptions if {@link DatatypeConfigurationException}
     * is thrown during initialisation of the Utility class.
     * Do not access directly! Use {@link #getXmlDataTypeFactory()} instead.
     */
    private static DatatypeFactory xmlDatatypeFactory;
    /**
     * Inits the {@link #xmlDatatypeFactory} if not already done.
     * @return the XML datatype factory
     * @throws IllegalStateException if a {@link DatatypeConfigurationException}
     * is encountered during {@link DatatypeFactory#newInstance()}
     */
    private static DatatypeFactory getXmlDataTypeFactory() throws IllegalStateException {
        if(xmlDatatypeFactory == null){
            try {
                xmlDatatypeFactory = DatatypeFactory.newInstance();
            } catch (DatatypeConfigurationException e) {
                throw new IllegalStateException("Unable to instantiate XML Datatype Factory!",e);
            }
        }
        return xmlDatatypeFactory;
    }
    @Override
    public Duration transform(RDFBackend backend, Node node) throws IllegalArgumentException {
        if(backend.isLiteral(node)) {
            return toDuration(backend.stringValue(node), false);
        } else {
            throw new IllegalArgumentException("cannot transform node of type "+
                node.getClass().getCanonicalName()+" to byte");
        }
    }
    
    private static Duration toDuration(String value, boolean nullAsZeroDuration) throws IllegalArgumentException,IllegalStateException{
        if(value == null){
            if(nullAsZeroDuration){
                return getXmlDataTypeFactory().newDuration(0);
            } else {
                throw new IllegalArgumentException("The parsed value MUST NOT be NULL. Parse \"boolean nullAsZeroDuration=true\" to enable creation of zero lenght durations for NULL values!");
            }
        } else {
            return getXmlDataTypeFactory().newDuration(value);
        }
    }

}