Struts example source code file (TemplateEngineManager.java)

This example Struts source code file (TemplateEngineManager.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Struts tags/keywords

configurationexception, default_template_type, enginefactory, enginefactory, hashmap, inject, lazyenginefactory, lazyenginefactory, map, string, string, templateengine, templateengine, unable, util

The Struts TemplateEngineManager.java source code

/*
 * $Id: TemplateEngineManager.java 651946 2008-04-27 13:41:38Z apetrelli $
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

import com.opensymphony.xwork2.config.ConfigurationException;
import com.opensymphony.xwork2.inject.Container;
import com.opensymphony.xwork2.inject.Inject;

/**
 * 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";

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

    
    Map<String,EngineFactory> templateEngines = new HashMap();
    Container container;
    String defaultTemplateType;
    
    @Inject(DEFAULT_TEMPLATE_TYPE_CONFIG_KEY)
    public void setDefaultTemplateType(String type) {
        this.defaultTemplateType = type;
    }
    
    @Inject
    public void setContainer(Container container) {
        this.container = container;
        Map<String,EngineFactory> map = new HashMap();
        Set<String> prefixes = container.getInstanceNames(TemplateEngine.class);
        for (String prefix : prefixes) {
            map.put(prefix, new LazyEngineFactory(prefix));
        }
        this.templateEngines = Collections.unmodifiableMap(map);
        
    }
    
    /**
     * 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 void registerTemplateEngine(String templateExtension, final TemplateEngine templateEngine) {
        templateEngines.put(templateExtension, new EngineFactory() {
            public TemplateEngine create() {
                return 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 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 {
            String type = defaultTemplateType;
            if (type != null) {
                templateType = type;
            }
        }
        return templateEngines.get(templateType).create();
    }

    /** Abstracts loading of the template engine */
    interface EngineFactory {
        public TemplateEngine create();
    }    

    /** 
     * Allows the template engine to be loaded at request time, so that engines that are missing
     * dependencies aren't accessed if never used.
     */
    class LazyEngineFactory implements EngineFactory {
        private String name;
        public LazyEngineFactory(String name) {
            this.name = name;
        }    
        public TemplateEngine create() {
            TemplateEngine engine = container.getInstance(TemplateEngine.class, name);
            if (engine == null) {
                throw new ConfigurationException("Unable to locate template engine: "+name);
            }
            return engine;
        }    
    }    
}