trunk/core/src/main/java/org/apache/struts2/views/freemarker/StrutsBeanWrapper.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.views.freemarker;

import java.util.Map;
import java.util.Set;

import freemarker.core.CollectionAndSequence;
import freemarker.ext.beans.BeansWrapper;
import freemarker.ext.beans.MapModel;
import freemarker.ext.util.ModelFactory;
import freemarker.template.ObjectWrapper;
import freemarker.template.SimpleSequence;
import freemarker.template.TemplateBooleanModel;
import freemarker.template.TemplateCollectionModel;
import freemarker.template.TemplateHashModelEx;
import freemarker.template.TemplateModel;
import freemarker.template.TemplateModelException;

/**
 * <!-- START SNIPPET: javadoc -->
 *
 * The StrutsBeanWrapper extends the default FreeMarker BeansWrapper and provides almost no change in functionality,
 * <b>except</b> for how it handles maps. Normally, FreeMarker has two modes of operation: either support for friendly
 * map built-ins (?keys, ?values, etc) but only support for String keys; OR no special built-in support (ie: ?keys
 * returns the methods on the map instead of the keys) but support for String and non-String keys alike. Struts
 * provides an alternative implementation that gives us the best of both worlds.
 *
 * <p/> It is possible that this special behavior may be confusing or can cause problems. Therefore, you can set the
 * <b>struts.freemarker.wrapper.altMap</b> property in struts.properties to false, allowing the normal BeansWrapper
 * logic to take place instead.
 *
 * <!-- END SNIPPET: javadoc -->
 */
public class StrutsBeanWrapper extends BeansWrapper {
    private static final boolean altMapWrapper
            = "true".equals(org.apache.struts2.config.Settings.get("struts.freemarker.wrapper.altMap"));

    public TemplateModel wrap(Object object) throws TemplateModelException {
        if (object instanceof TemplateBooleanModel) {
            return super.wrap(object);
        }

        // attempt to get the best of both the SimpleMapModel and the MapModel of FM.
        if (altMapWrapper && object instanceof Map) {
            return getInstance(object, FriendlyMapModel.FACTORY);
        }

        return super.wrap(object);
    }

    /**
     * Attempting to get the best of both worlds of FM's MapModel and SimpleMapModel, by reimplementing the isEmpty(),
     * keySet() and values() methods. ?keys and ?values built-ins are thus available, just as well as plain Map
     * methods.
     */
    private final static class FriendlyMapModel extends MapModel implements TemplateHashModelEx {
        static final ModelFactory FACTORY = new ModelFactory() {
            public TemplateModel create(Object object, ObjectWrapper wrapper) {
                return new FriendlyMapModel((Map) object, (BeansWrapper) wrapper);
            }
        };

        public FriendlyMapModel(Map map, BeansWrapper wrapper) {
            super(map, wrapper);
        }

        public boolean isEmpty() {
            return ((Map) object).isEmpty();
        }

        protected Set keySet() {
            return ((Map) object).keySet();
        }

        public TemplateCollectionModel values() {
            return new CollectionAndSequence(new SimpleSequence(((Map) object).values(), wrapper));
        }
    }
}