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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.ext.jsp;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.jsp.JspFactory;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.el.ELException;
import javax.servlet.jsp.el.ExpressionEvaluator;
import javax.servlet.jsp.el.VariableResolver;

import freemarker.log.Logger;
import freemarker.template.TemplateModelException;

/**
 * Don't use this class; it's only public to work around Google App Engine Java
 * compliance issues. FreeMarker developers only: treat this class as package-visible.
 * 
 * Implementation of PageContext that contains JSP 2.0 specific methods.
 */
public class _FreeMarkerPageContext2 extends FreeMarkerPageContext {
    private static final Logger LOG = Logger.getLogger("freemarker.jsp");

    static {
        if (JspFactory.getDefaultFactory() == null) {
            JspFactory.setDefaultFactory(new FreeMarkerJspFactory2());
        }
        LOG.debug("Using JspFactory implementation class " + 
                JspFactory.getDefaultFactory().getClass().getName());
    }

    public _FreeMarkerPageContext2() throws TemplateModelException {
        super();
    }

    /**
     * Attempts to locate and manufacture an expression evaulator instance. For this
     * to work you must have the Apache Commons-EL package in the classpath. If
     * Commons-EL is not available, this method will throw an UnsupportedOperationException. 
     */
    @Override
    public ExpressionEvaluator getExpressionEvaluator() {
        try {
            Class type = Thread.currentThread().getContextClassLoader().loadClass
                    ("org.apache.commons.el.ExpressionEvaluatorImpl");
            return (ExpressionEvaluator) type.newInstance();
        } catch (Exception e) {
            throw new UnsupportedOperationException("In order for the getExpressionEvaluator() " +
                "method to work, you must have downloaded the apache commons-el jar and " +
                "made it available in the classpath.");
        }
    }

    /**
     * Returns a variable resolver that will resolve variables by searching through
     * the page scope, request scope, session scope and application scope for an
     * attribute with a matching name.
     */
    @Override
    public VariableResolver getVariableResolver() {
        final PageContext ctx = this;

        return new VariableResolver() {
            @Override
            public Object resolveVariable(String name) throws ELException {
                return ctx.findAttribute(name);
            }
        };
    }

    /**
     * Includes the specified path. The flush argument is ignored!
     */
    @Override
    public void include(String path, boolean flush) throws IOException, ServletException {
        super.include(path);
    }
}