src/main/java/freemarker/template/AdapterTemplateModel.java

/*
 * 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.template;

/**
 * A {@link TemplateModel} that can be unwrapped and then it considers a provided desired (hint) class. This is
 * useful when multiple languages has to communicate with each other through FreeMarker. For example, if we have a
 * model that wraps a Jython object, then we have to unwrap that differently when we pass it to plain Java method and
 * when we pass it to a Jython method.
 * 
 * <p>This is rarely implemented by applications. It is typically implemented by the model classes belonging to
 * {@link ObjectWrapper}-s.
 */
public interface AdapterTemplateModel extends TemplateModel {
    /**
     * Retrieves the underlying object, or some other object semantically 
     * equivalent to its value narrowed by the class hint.   
     * @param hint the desired class of the returned value. An implementation 
     * should make reasonable effort to retrieve an object of the requested 
     * class, but if that is impossible, it must at least return the underlying 
     * object as-is. As a minimal requirement, an implementation must always 
     * return the exact underlying object when 
     * <tt>hint.isInstance(underlyingObject)</tt> holds. When called 
     * with <tt>java.lang.Object.class</tt>, it should return a generic Java 
     * object (i.e. if the model is wrapping a scripting language object that is
     * further wrapping a Java object, the deepest underlying Java object should
     * be returned). 
     * @return the underlying object, or its value accommodated for the hint
     * class.
     */
    public Object getAdaptedObject(Class hint);
}