eu.esdihumboldt.hale.doc.util.content.AbstractVelocityContent.java Source code

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Here is the source code for eu.esdihumboldt.hale.doc.util.content.AbstractVelocityContent.java

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/*
 * Copyright (c) 2012 Data Harmonisation Panel
 * 
 * All rights reserved. This program and the accompanying materials are made
 * available under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the License,
 * or (at your option) any later version.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution. If not, see <http://www.gnu.org/licenses/>.
 * 
 * Contributors:
 *     HUMBOLDT EU Integrated Project #030962
 *     Data Harmonisation Panel <http://www.dhpanel.eu>
 */

package eu.esdihumboldt.hale.doc.util.content;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Locale;
import java.util.concurrent.Callable;

import org.apache.commons.io.IOUtils;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.eclipse.help.IHelpContentProducer;

import com.google.common.io.Files;

/**
 * Help content based on velocity templates. Use
 * {@link #getContentFromTemplate(String, String, Callable)} in your
 * {@link #getInputStream(String, String, Locale)} implementation.
 * 
 * @author Simon Templer
 */
public abstract class AbstractVelocityContent implements IHelpContentProducer {

    /**
     * The velocity engine used for content generation.
     */
    private VelocityEngine ve;

    /**
     * The temporary directory where the template is copied to, and the already
     * generated is stored.
     */
    private File tempDir;

    /**
     * Generate content from the template and the given context factory. If
     * called more than once with the same id, the previously generated content
     * for that id is returned.
     * 
     * @param contentId the content id
     * @param templateId the template id (there may be multiple templates)
     * @param contextFactory the context factory, is called once or not at all
     * @return the content input stream to return in
     *         {@link #getInputStream(String, String, Locale)}
     * @throws Exception if an error occurs creating the content
     */
    protected InputStream getContentFromTemplate(String contentId, String templateId,
            Callable<VelocityContext> contextFactory) throws Exception {
        init(templateId);

        // creates the template file into the temporary directory
        // if it doesn't already exist
        File contentFile = new File(tempDir, templateId + "_" + contentId + ".html");
        if (!contentFile.exists()) {
            // get the template context
            VelocityContext context = contextFactory.call();

            // get the template
            Template template = ve.getTemplate(templateId + ".vm", "UTF-8");

            // write to the file
            FileWriter fw = new FileWriter(contentFile);
            template.merge(context, fw);

            fw.close();

            contentFile.deleteOnExit();
        }

        return new FileInputStream(contentFile);
    }

    /**
     * Initialize temporary directory and template engine.
     * 
     * @param templateId the template id (there may be multiple templates)
     * 
     * @throws Exception if an error occurs during the initialization
     */
    private void init(String templateId) throws Exception {
        synchronized (this) {
            // engine initialization
            if (ve == null) {
                ve = new VelocityEngine();
                // create a temporary directory
                tempDir = Files.createTempDir();
                tempDir.deleteOnExit();

                ve.setProperty("file.resource.loader.path", tempDir.getAbsolutePath());

                // initialize VelocityEngine
                ve.init();
            }

            File templateFile = new File(tempDir, templateId + ".vm");
            if (!templateFile.exists()) {
                OutputStream fos = new BufferedOutputStream(new FileOutputStream(templateFile));
                InputStream stream = getTemplate(templateId);

                // copy the InputStream into FileOutputStream
                IOUtils.copy(stream, fos);

                stream.close();
                fos.close();

                templateFile.deleteOnExit();
            }
        }
    }

    /**
     * Get the template content.
     * 
     * @param templateId the template id (there may be multiple templates)
     * 
     * @return the template as input stream
     * @throws Exception if an error occurs retrieving the template
     */
    protected abstract InputStream getTemplate(String templateId) throws Exception;

}