trunk/core/src/main/java/org/apache/struts2/components/template/TemplateEngineManager.java

/*
 * $Id$
 *
 * Copyright 2006 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.struts2.components.template;

import java.util.HashMap;
import java.util.Map;

import org.apache.struts2.config.Settings;

/**
 * The TemplateEngineManager will return a template engine for the template
 */
public class TemplateEngineManager {
    public static final String DEFAULT_TEMPLATE_TYPE_CONFIG_KEY = "struts.ui.templateSuffix";

    private static final TemplateEngineManager MANAGER = new TemplateEngineManager();

    /** The default template extenstion is <code>ftl</code>. */
    public static final String DEFAULT_TEMPLATE_TYPE = "ftl";

    Map templateEngines = new HashMap();

    private TemplateEngineManager() {
        templateEngines.put("ftl", new FreemarkerTemplateEngine());
        templateEngines.put("vm", new VelocityTemplateEngine());
        templateEngines.put("jsp", new JspTemplateEngine());
    }

    /**
     * Registers the given template engine.
     * <p/>
     * Will add the engine to the existing list of known engines.
     * @param templateExtension  filename extension (eg. .jsp, .ftl, .vm).
     * @param templateEngine     the engine.
     */
    public static void registerTemplateEngine(String templateExtension, TemplateEngine templateEngine) {
        MANAGER.templateEngines.put(templateExtension, templateEngine);
    }

    /**
     * Gets the TemplateEngine for the template name. If the template name has an extension (for instance foo.jsp), then
     * this extension will be used to look up the appropriate TemplateEngine. If it does not have an extension, it will
     * look for a Configuration setting "struts.ui.templateSuffix" for the extension, and if that is not set, it
     * will fall back to "ftl" as the default.
     *
     * @param template               Template used to determine which TemplateEngine to return
     * @param templateTypeOverride Overrides the default template type
     * @return the engine.
     */
    public static TemplateEngine getTemplateEngine(Template template, String templateTypeOverride) {
        String templateType = DEFAULT_TEMPLATE_TYPE;
        String templateName = template.toString();
        if (templateName.indexOf(".") > 0) {
            templateType = templateName.substring(templateName.indexOf(".") + 1);
        } else if (templateTypeOverride !=null && templateTypeOverride.length() > 0) {
            templateType = templateTypeOverride;
        } else if (Settings.isSet(DEFAULT_TEMPLATE_TYPE_CONFIG_KEY)) {
            templateType = (String) Settings.get(DEFAULT_TEMPLATE_TYPE_CONFIG_KEY);
        }
        return (TemplateEngine) MANAGER.templateEngines.get(templateType);
    }


}