MontiCoreTemplateLoader.java

/*
 * ******************************************************************************
 * MontiCore Language Workbench
 * Copyright (c) 2015, MontiCore, All rights reserved.
 *
 * This project is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 3.0 of the License, or (at your option) any later version.
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this project. If not, see <http://www.gnu.org/licenses/>.
 * ******************************************************************************
 */

package de.monticore.generating.templateengine.freemarker;

import java.net.URL;

import de.se_rwth.commons.logging.Log;
import freemarker.cache.URLTemplateLoader;

/**
 * Is used to load templates with a given {@link ClassLoader}.
 * 
 * @author Arne Haber
 * 
 */
public class MontiCoreTemplateLoader extends URLTemplateLoader {
  
  /** the used class loader */
  private final ClassLoader classLoader;
  
  /**
   * Creates a new {@link MontiCoreTemplateLoader} that uses the given class loader to load
   * FreeMarker templates from the class path
   * 
   * @param classLoader
   */
  public MontiCoreTemplateLoader(ClassLoader classLoader) {
    Log.errorIfNull(classLoader,
        "0xA4049 ClassLoader must not be null in MontiCoreTemplateLoader constructor.");
    this.classLoader = classLoader;
  }
  
  /**
   * Resolves the location of a template on the local machine.
   * 
   * @see freemarker.cache.URLTemplateLoader#getURL(java.lang.String)
   * @param templateName The qualified name of the Template. Example: "cd2data.core.Attribute" or
   * "cd2data/core/Attribute" or "cd2data.core.Attribute.ftl"
   * @return URL of the template on the local machine. Example:
   * "jar:file:/C:/.../dex/gtr/target/dex-gtr-0.9.4-SNAPSHOT.jar!/cd2data/core/Attribute.ftl" (this
   * is from the toString method of the URL object)
   */
  @Override
  protected URL getURL(String templateName) {
    Log.debug("Requested template " + templateName, MontiCoreTemplateLoader.class.getName());
    
    // Since the input is almost always dot separated, this method just goes ahead and converts it
    // without checking, only in the rare case that this procedure is unsuccessful are
    // alternatives considered
    URL result = classLoader.getResource(templateName.replace('.', '/').concat(FreeMarkerTemplateEngine.FM_FILE_EXTENSION));
    if (result != null) {
      return result;
    }
    // if the search was still unsuccessful the method tries once more and checks if the problem
    // was that the original input already had the .ftl suffix (in that case the previous
    // procedure would've added this suffix again).
    // Note: This part of the procedure was placed here because it is almost never chosen.
    if (templateName.endsWith(FreeMarkerTemplateEngine.FM_FILE_EXTENSION)) {
      String newName = templateName.substring(0,
          templateName.length() - FreeMarkerTemplateEngine.FM_FILE_EXTENSION.length());
      result = classLoader.getResource(newName.replace('.', '/').concat(FreeMarkerTemplateEngine.FM_FILE_EXTENSION));
    } else {
      result = classLoader.getResource(templateName);
    }
    return result;
  }
  
}