platform/sensinact-utils/src/main/java/org/eclipse/sensinact/gateway/util/PropertyUtils.java

/*
 * Copyright (c) 2017 CEA.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    CEA - initial API and implementation
 */
package org.eclipse.sensinact.gateway.util;

import org.osgi.framework.BundleContext;

import java.util.Properties;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 *
 */
public class PropertyUtils {
    private static final Pattern PATTERN = Pattern.compile("\\$\\(([^\\)\\(\\$]+)\\)");

    /**
     * Search and return the value of the property
     * which key is passed as parameter ; The search order
     * is :
     * - the {@link Properties} passed as parameter first
     * - then the {@link BundleContext};
     * - and finally in the system
     *
     * @param context    the {@link BundleContext}
     * @param properties the {@link Properties}
     * @param key        the searched property's key
     * @return the searched property's value
     */
    public static Object getProperty(BundleContext context, Properties properties, String key) {
        if (key == null) {
            return null;
        }
        String builtKey = key;
        while (true) {
            Matcher matcher = PATTERN.matcher(builtKey);
            if (!matcher.find()) {
                break;
            }
            int start = matcher.start();
            int end = matcher.end();

            StringBuilder builder = new StringBuilder();
            if (start > 0) {
                builder.append(key.substring(0, start));
            }
            Object property = getProperty(context, properties, matcher.group(1));
            if (property == null) {
                return null;
            }
            builder.append(property);
            if (end < builtKey.length()) {
                builder.append(builtKey.substring(end, builtKey.length()));
            }
            builtKey = builder.toString();
        }
        Object value = null;

        if ((value = (properties == null ? null : properties.get(builtKey))) == null && (value = context.getProperty(builtKey)) == null) {
            value = System.getProperty(builtKey);
        }
        return value;
    }
}