src/main/java/freemarker/ext/beans/EnumerationModel.java

/*
 * Copyright (c) 2003 The Visigoth Software Society. All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
 *        Visigoth Software Society (http://www.visigoths.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
 *
 * 4. Neither the name "FreeMarker", "Visigoth", nor any of the names of the 
 *    project contributors may be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact visigoths@visigoths.org.
 *
 * 5. Products derived from this software may not be called "FreeMarker" or "Visigoth"
 *    nor may "FreeMarker" or "Visigoth" appear in their names
 *    without prior written permission of the Visigoth Software Society.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE VISIGOTH SOFTWARE SOCIETY OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Visigoth Software Society. For more
 * information on the Visigoth Software Society, please see
 * http://www.visigoths.org/
 */

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;

/**
 * <p>A class that adds {@link TemplateModelIterator} functionality to the
 * {@link Enumeration} interface implementers. 
 * </p> <p>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.</p>
 * @author Attila Szegedi
 */

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 <tt>&lt;foreach></tt> 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();
    }
}