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Merge a XML file with a Velocity template
There is a newer version: 1.8.8
/******************************************************
 * Merge XML with a Velocity template
 * 
 *
 * Copyright (C) 2012 by Peter Hedenskog (http://peterhedenskog.com)
 *
 ******************************************************
 *
 * Licensed 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 com.soulgalore.velocity;

import java.io.File;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;
import java.util.Set;

import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.app.VelocityEngine;
import org.jdom2.Document;
import org.jdom2.JDOMException;
import org.jdom2.input.SAXBuilder;
import org.jdom2.input.sax.XMLReaderSAX2Factory;


/**
 * Merge a XML file with a Velocity template. 
 *  java -jar xml-velocity-1.0-full.jar test.xml test.vm test.properties newfile.xml
 * 	
 * 
 * 
 * The parameters:
 * 

 * the xml file
 * the Velocity template file
 * the properties file, key/vale will be added to the Velocity context, used
 * when merged
 * the output file name, if excluded the merge will be printed to system.out
 * 
 * 
 * 
 * 
 * The document is added to the context with {@link #CONTEXT_DOCUMENT} as key.
 * 
 *  You can also add objects to the velocity context by configuration, in the properties file, add:
 * 
velocity.context.object.1=CLASSNAME:KEYNAME 
 * And make sure the class exists in the classpath and have a constructor without arguments. See this example:
 *  * velocity.context.object.1=org.apache.velocity.tools.generic.MathTool:math
 * velocity.context.object.2=org.apache.velocity.tools.generic.EscapeTool:esc
 * velocity.context.object.3=org.apache.commons.math3.stat.descriptive.DescriptiveStatistics:stats
 * velocity.context.object.4=com.soulgalore.velocity.HostTool:host
 * 
 * 
 * 
 */
public class MergeXMLWithVelocity {

	/**
	 * The name of the xml document, added to the context.
	 */
	public static final String CONTEXT_DOCUMENT = "document";

	public static final String CONTEXT_PROPERTY_OBJECT = "velocity.context.object";

	private final VelocityContext context = new VelocityContext();

	private final VelocityEngine ve;

	MergeXMLWithVelocity(Properties properties) {

		ve = new VelocityEngine(properties);
		ve.init();

		Map keyAndClasses = getClasses(properties);
		for (Entry value : keyAndClasses.entrySet()) {
			try {
				Class clazz = Class.forName(value.getValue());
				context.put(value.getKey(), clazz.newInstance());
			} catch (Exception e) {
				System.err.println("Couldn't instantiate class:"
						+ value.getValue() + " with key:" + value.getKey()
						+ " and put it in Velocity context:" + e.toString());
			}

		}

		final Enumeration e = properties.propertyNames();

		while (e.hasMoreElements()) {
			final String key = (String) e.nextElement();
			context.put(key, properties.getProperty(key));
		}
	}

	/**
	 * Merge a xml file with Velocity template. The third parameter is the
	 * properties file, where the key/value is added to the velocity context.
	 * The fourth parameter is the output file. If not included, the result is
	 * printed to system.out.
	 * 
	 * @param args
	 *            are file.xml template.vm properties.prop [output.file]
	 * @throws JDOMException
	 *             if the xml file couldn't be parsed
	 * @throws IOException
	 *             couldn't find one of the files
	 */
	public static void main(String[] args) throws JDOMException, IOException {

		if (args.length < 3) {
			System.out
					.println("Missing input files. XMLToVelocity file.xml template.vm prop.properties [output.file]");
			return;
		}

		final Properties properties = new Properties();
		final File prop = new File(args[2]);

		if (prop.exists())
			properties.load(new FileReader(prop));
		else
			throw new IOException("Couldn't find the property file:"
					+ prop.getAbsolutePath());

		final MergeXMLWithVelocity xtv = new MergeXMLWithVelocity(properties);
		xtv.create(args);
	}

	void create(String[] args) throws JDOMException, IOException {

		final String result = merge(args[0], args[1]);
		if (args.length < 4)
			System.out.println(result);
		else {
			final PrintWriter out = new PrintWriter(new FileOutputStream(
					args[3]));
			out.write(result);
			out.close();
		}

	}

	String merge(String xml, String template) throws JDOMException, IOException {

		final File xmlFile = new File(xml);
		final SAXBuilder b = new SAXBuilder(new XMLReaderSAX2Factory(false));
		final Document doc = b.build(xmlFile);

		context.put(CONTEXT_DOCUMENT, doc);

		final StringWriter writer = new StringWriter();
		final Template fromTemplate = ve.getTemplate(template);
		fromTemplate.merge(context, writer);
		return writer.toString();

	}

	private Map getClasses(Properties properties) {

		Map keyAndClass = new HashMap();
		Set keys = properties.stringPropertyNames();
		for (String key : keys) {
			if (key.startsWith(CONTEXT_PROPERTY_OBJECT)) {
				String value = properties.getProperty(key);
				String className = value.substring(0, value.indexOf(":"));
				String contextKey = value.substring(value.indexOf(":") + 1,
						value.length());
				keyAndClass.put(contextKey, className);
			}
		}
		return keyAndClass;
	}
}