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Google App Engine compliant variation of FreeMarker. FreeMarker is a "template engine"; a generic tool to generate text output based on templates.
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/*
 * 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 freemarker.ext.beans;

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

import freemarker.ext.util.ModelFactory;
import freemarker.template.ObjectWrapper;
import freemarker.template.TemplateMethodModelEx;
import freemarker.template.TemplateModel;
import freemarker.template.TemplateModelException;

/**
 * A special case of {@link BeanModel} that adds implementation
 * for {@link TemplateMethodModelEx} on map objects that is a shortcut for the
 * {@code Map.get()} method. Note that if the passed argument itself is a
 * reflection-wrapper model, then the map lookup will be performed using the
 * wrapped object as the key. Note that you can call {@code get()} using the
 * {@code map.key} syntax inherited from {@link BeanModel} as well, 
 * however in that case the key is always a string.
 * The class itself does not implement the {@link freemarker.template.TemplateCollectionModel}.
 * You can, however use {@code map.entrySet()}, {@code map.keySet()}, or
 * {@code map.values()} to obtain {@link freemarker.template.TemplateCollectionModel} instances for 
 * various aspects of the map.
 */
public class MapModel
extends
    StringModel
implements
    TemplateMethodModelEx {
    static final ModelFactory FACTORY =
        new ModelFactory()
        {
            @Override
            public TemplateModel create(Object object, ObjectWrapper wrapper) {
                return new MapModel((Map) object, (BeansWrapper) wrapper);
            }
        };

    /**
     * Creates a new model that wraps the specified map object.
     * @param map the map object to wrap into a model.
     * @param wrapper the {@link BeansWrapper} associated with this model.
     * Every model has to have an associated {@link BeansWrapper} instance. The
     * model gains many attributes from its wrapper, including the caching 
     * behavior, method exposure level, method-over-item shadowing policy etc.
     */
    public MapModel(Map map, BeansWrapper wrapper) {
        super(map, wrapper);
    }

    /**
     * The first argument is used as a key to call the map's {@code get} method.
     */
    @Override
    public Object exec(List arguments)
    throws TemplateModelException {
        Object key = unwrap((TemplateModel) arguments.get(0));
        return wrap(((Map) object).get(key));
    }

    /**
     * Overridden to invoke the generic get method by casting to Map instead of 
     * through reflection - should yield better performance.
     */
    @Override
    protected TemplateModel invokeGenericGet(Map keyMap, Class clazz, String key)
    throws TemplateModelException {
        Map map = (Map) object;
        Object val = map.get(key);
        if (val == null) {
            if (key.length() == 1) {
                // just check for Character key if this is a single-character string
                Character charKey = Character.valueOf(key.charAt(0));
                val = map.get(charKey);
                if (val == null && !(map.containsKey(key) || map.containsKey(charKey))) {
                    return UNKNOWN;
                }
            } else if (!map.containsKey(key)) {
                return UNKNOWN;
            }
        }
        return wrap(val);
    }

    @Override
    public boolean isEmpty() {
        return ((Map) object).isEmpty() && super.isEmpty();
    }

    @Override
    public int size() {
        return keySet().size();
    }

    @Override
    protected Set keySet() {
        Set set = super.keySet();
        set.addAll(((Map) object).keySet());
        return set;
    }
}