src/main/java/freemarker/template/ObjectWrapper.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
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 * 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.template;

import java.util.List;
import java.util.Map;
import java.util.ResourceBundle;

import freemarker.ext.beans.BeansWrapper;
import freemarker.ext.util.WrapperTemplateModel;

/**
 * Maps Java objects to the type-system of FreeMarker Template Language (see the {@link TemplateModel}
 * interfaces). Thus this is what decides what parts of the Java objects will be accessible in the templates and how.
 * 
 * <p>For example, with a {@link BeansWrapper} both the items of {@link Map} and the JavaBean properties (the getters)
 * of an object are accessible in template uniformly with the {@code myObject.foo} syntax, where "foo" is the map key or
 * the property name. This is because both kind of object is wrapped by {@link BeansWrapper} into a
 * {@link TemplateHashModel} implementation that will call {@link Map#get(Object)} or the getter method, transparently
 * to the template language.
 * 
 * @see Configuration#setObjectWrapper(ObjectWrapper)
 */
public interface ObjectWrapper {
    
    /**
     * An {@link ObjectWrapper} that exposes the object methods and JavaBeans properties as hash elements, and has
     * custom handling for Java {@link Map}-s, {@link ResourceBundle}-s, etc. It doesn't treat
     * {@link org.w3c.dom.Node}-s and Jython objects specially, however.
     */
    ObjectWrapper BEANS_WRAPPER = BeansWrapper.getDefaultInstance();

    /**
     * The default object wrapper implementation, focusing on backward compatibility and out-of-the box extra features.
     * Extends {@link BeansWrapper} with the special handling of {@link org.w3c.dom.Node}-s (for XML processing) and
     * Jython objects. However, for backward compatibility, it also somewhat downgrades {@link BeansWrapper} by using   
     * {@link SimpleHash} for {@link Map}-s, {@link SimpleSequence} for {@link List}-s and collections/arrays.
     * Furthermore it uses {@link SimpleScalar}, {@link SimpleNumber} to wrap {@link String}-s and {@link Number}-s,
     * although this is not considered to be harmful.    
     */
    ObjectWrapper DEFAULT_WRAPPER = DefaultObjectWrapper.instance;

    /**
     * Object wrapper that uses {@code SimpleXXX} wrappers only.
     * It behaves like the {@link #DEFAULT_WRAPPER}, but for objects
     * that it does not know how to wrap as a {@code SimpleXXX} it 
     * throws an exception. It makes no use of reflection-based 
     * exposure of anything, which may makes it a good candidate for security-restricted applications. 
     */
    ObjectWrapper SIMPLE_WRAPPER = SimpleObjectWrapper.instance;
    
    /**
     * Makes a {@link TemplateModel} out of a non-{@link TemplateModel} object, usually by "wrapping" it into a
     * {@link TemplateModel} implementation that delegates to the original object.
     * 
     * @param obj The object to wrap into a {@link TemplateModel}. If the it already implements {@link TemplateModel},
     *      it should just return the object as is.
     * 
     * @return a {@link TemplateModel} wrapper of the object passed in. To support un-wrapping, you may consider the
     *     return value to implement {@link WrapperTemplateModel} and {@link AdapterTemplateModel}.
     */
    TemplateModel wrap(Object obj) throws TemplateModelException;
    
}