services/billing-aws/src/main/java/com/epam/dlab/configuration/FreeMarkerConfig.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 com.epam.dlab.configuration;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import com.google.common.base.Throwables;

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;

/** Provides Apache FreeMarker the template engine for the billing configuration.
 */
public class FreeMarkerConfig {
	
	/** Create and return the input stream for the configuration file.
	 * @param filename the name of configuration file.
	 * @throws IOException
	 */
	public InputStream getInputStream(final String filename) throws IOException {
		try {
			Configuration conf = new Configuration(Configuration.VERSION_2_3_22);
			Template template = new Template("billing-config", new FileReader(new File(filename)), conf);
			Map<String, Object> dataModel = getDataModel();
			
			ByteArrayOutputStream streamBuffer = new ByteArrayOutputStream();
			template.process(dataModel, new OutputStreamWriter(streamBuffer, StandardCharsets.UTF_8));
			byte[] buffer = streamBuffer.toByteArray();
			
			return new ByteArrayInputStream(buffer);
		} catch (TemplateException e) {
			throw Throwables.propagate(e);
		}
	}

	/** Create and return JVM and OS properties.
	 */
	private Map<String, Object> getDataModel() {
		Map<String, Object> dataModel = new HashMap<>();
		
		Iterator<Object> sysProps = System.getProperties().keySet().iterator();
		while (sysProps.hasNext()) {
			String key = (String) sysProps.next();
			dataModel.put(key, System.getProperties().getProperty(key));
		}
		dataModel.putAll(System.getenv());

		dataModel.put("env", System.getenv());
		dataModel.put("sys", System.getProperties());

		return dataModel;
	}
}