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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.template.utility;

import java.util.List;

import freemarker.ext.beans.BeansWrapper;
import freemarker.template.TemplateMethodModelEx;
import freemarker.template.TemplateModelException;

/**
 * An object that you can make available in a template
 * to instantiate arbitrary beans-wrapped objects in a template.
 * Beware of this class's security implications. It allows
 * the instantiation of arbitrary objects and invoking 
 * methods on them. Usage is something like:
 * 

 * 
myDataModel.put("objectConstructor", new ObjectConstructor());
 * 

 * 
And then from your FTL code:
 * 

 * 
<#assign aList = objectConstructor("java.util.ArrayList", 100)>
 */
public class ObjectConstructor implements TemplateMethodModelEx {
    @Override
    public Object exec(List args) throws TemplateModelException {
        if (args.isEmpty()) {
            throw new TemplateModelException("This method must have at least one argument, the name of the class to instantiate.");
        }
        String classname = args.get(0).toString();
        Class cl = null;
        try {
            cl = ClassUtil.forName(classname);
        } catch (Exception e) {
            throw new TemplateModelException(e.getMessage());
        }
        BeansWrapper bw = BeansWrapper.getDefaultInstance();
        Object obj = bw.newInstance(cl, args.subList(1, args.size()));
        return bw.wrap(obj);
    }
}