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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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/*
 * Copyright 2014 Attila Szegedi, Daniel Dekany, Jonathan Revusky
 * 
 * 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 freemarker.ext.beans;

import java.util.Enumeration;
import java.util.NoSuchElementException;

import freemarker.template.TemplateCollectionModel;
import freemarker.template.TemplateModel;
import freemarker.template.TemplateModelException;
import freemarker.template.TemplateModelIterator;

/**
 * A class that adds {@link TemplateModelIterator} functionality to the
 * {@link Enumeration} interface implementers. 
 * 
 Using the model as a collection model is NOT thread-safe, as 
 * enumerations are inherently not thread-safe.
 * Further, you can iterate over it only once. Attempts to call the
 * {@link #iterator()} method after it was already driven to the end once will 
 * throw an exception.
 */

public class EnumerationModel
extends
    BeanModel
implements
    TemplateModelIterator,
    TemplateCollectionModel
{
    private boolean accessed = false;
    
    /**
     * Creates a new model that wraps the specified enumeration object.
     * @param enumeration the enumeration 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 EnumerationModel(Enumeration enumeration, BeansWrapper wrapper)
    {
        super(enumeration, wrapper);
    }

    /**
     * This allows the enumeration to be used in a <#list> block.
     * @return "this"
     */
    public TemplateModelIterator iterator() throws TemplateModelException
    {
        synchronized(this) {
            if(accessed) {
                throw new TemplateModelException(
                    "This collection is stateful and can not be iterated over the" +
                    " second time.");
            }
            accessed = true;
        }
        return this;
    }
    
    /**
     * Calls underlying {@link Enumeration#nextElement()}.
     */
    public boolean hasNext() {
        return ((Enumeration)object).hasMoreElements();
    }


    /**
     * Calls underlying {@link Enumeration#nextElement()} and wraps the result.
     */
    public TemplateModel next()
    throws
        TemplateModelException
    {
        try {
            return wrap(((Enumeration)object).nextElement());
        }
        catch(NoSuchElementException e) {
            throw new TemplateModelException(
                "No more elements in the enumeration.");
        }
    }

    /**
     * Returns {@link Enumeration#hasMoreElements()}. Therefore, an
     * enumeration that has no more element evaluates to false, and an 
     * enumeration that has further elements evaluates to true.
     */
    public boolean getAsBoolean() {
        return hasNext();
    }
}