source: vlo/branches/vlo-3.0/vlo-web-app/src/main/java/eu/clarin/cmdi/vlo/service/impl/XmlTransformationServiceImpl.java @ 4669

/*
 * Copyright (C) 2014 CLARIN
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package eu.clarin.cmdi.vlo.service.impl;

import eu.clarin.cmdi.vlo.service.XmlTransformationService;
import java.io.IOException;
import java.io.InputStream;
import java.io.StringWriter;
import java.net.URL;
import java.util.Properties;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Templates;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Transforms input documents to a fixed stylesheet (determined on construction)
 * using JAXP XSLT support.
 *
 * Thread-safe
 *
 * @author twagoo
 */
public class XmlTransformationServiceImpl implements XmlTransformationService {

    private final static Logger logger = LoggerFactory.getLogger(XmlTransformationServiceImpl.class);

    private final Templates template;
    private final Properties transformationProperties;

    /**
     *
     * @param xsltSource source of the stylesheet to use in {@link #transformXml(java.net.URL)
     * }
     * @
     * param properties transformation properties to be passed to the
     * transformer object before transformation
     * @throws TransformerConfigurationException if the transformer could not be
     * configured correctly
     */
    public XmlTransformationServiceImpl(Source xsltSource, Properties properties) throws TransformerConfigurationException {
        final TransformerFactory transformerFactory = TransformerFactory.newInstance();
        // create a template to derive transformers from, which makes this thread safe
        this.template = transformerFactory.newTemplates(xsltSource);
        this.transformationProperties = properties;

        logger.debug("Transformation service created for {} with properties {}", xsltSource, properties);
    }

    /**
     *
     * @param location location of XML document to transform (should not be
     * null)
     * @return the result of the XML transformation as a string
     * @throws TransformerException If an unrecoverable error occurs during the
     * course of the transformation or while opening the input stream.
     */
    @Override
    public String transformXml(URL location) throws TransformerException {
        logger.debug("Transforming {}", location);

        // create a transformer based on the template
        final Transformer transformer = template.newTransformer();
        transformer.setOutputProperties(transformationProperties);

        try {
            final InputStream inStream = location.openStream();
            final StringWriter outWriter = new StringWriter();

            // make input/output objects
            final Source source = new StreamSource(inStream);
            final Result result = new StreamResult(outWriter);

            // perform actual transformation (this will also close the streams)
            transformer.transform(source, result);

            // result has been written to string writer, return contents
            return outWriter.toString();
        } catch (IOException ex) {
            throw new TransformerException("Error while opening input stream for " + location.toString(), ex);
        }

    }

}