pdfbox-trunk/preflight/src/main/java/org/apache/pdfbox/preflight/metadata/RDFAboutAttributeConcordanceValidation.java
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package org.apache.pdfbox.preflight.metadata;

import java.util.List;

import org.apache.pdfbox.preflight.exception.ValidationException;
import org.apache.xmpbox.XMPMetadata;
import org.apache.xmpbox.schema.XMPSchema;

/**
 * Class which checks that all elements within an rdf:RDF have the same value for their rdf:about
 * attributes.
 *
 * @author Germain Costenobel
 *
 */
public class RDFAboutAttributeConcordanceValidation
{

    /**
     *
     * @param metadata the XMP metadata.
     * @throws DifferentRDFAboutException
     * @throws ValidationException
     */
    public void validateRDFAboutAttributes(XMPMetadata metadata) throws ValidationException, DifferentRDFAboutException
    {

        List<XMPSchema> schemas = metadata.getAllSchemas();
        if (schemas.isEmpty())
        {
            throw new ValidationException("No schema found in the given metadata representation");
        }

        String about = schemas.get(0).getAboutValue();

        // rdf:description must have an rdf:about attribute
        for (XMPSchema xmpSchema : schemas)
        {
            // each rdf:Description must have the same rdf:about (or an empty one)
            String schemaAboutValue = xmpSchema.getAboutValue();
            if (!("".equals(schemaAboutValue) || "".equals(about) || about.equals(schemaAboutValue)))
            {
                throw new DifferentRDFAboutException();
            }

            if ("".equals(about))
            {
                about = schemaAboutValue;
            }
        }
    }

    public static class DifferentRDFAboutException extends Exception
    {

        private static final long serialVersionUID = 1L;

        public DifferentRDFAboutException()
        {
            super("all rdf:about in RDF:rdf must have the same value");
        }
    }
}
