PropertyUtils.java

/**
 * Copyright 2011 the original author or authors.
 *
 * 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 org.bricket.web.util;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.Map.Entry;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import brix.exception.BrixException;

public final class PropertyUtils {
    private static final Logger LOG = LoggerFactory.getLogger(PropertyUtils.class);

    private PropertyUtils() {
        super();
    }

    /**
     * Loads properties from a classpath resource
     * 
     * @param resource
     * @param throwExceptionIfNotFound
     * @return loaded properties
     */
    public static Properties loadFromClassPath(String resource, boolean throwExceptionIfNotFound) {
        URL url = PropertyUtils.class.getClassLoader().getResource(resource);

        if (url == null) {
            if (throwExceptionIfNotFound) {
                throw new IllegalStateException("Could not find classpath properties resource: " + resource);
            } else {
                return new Properties();
            }
        }

        InputStream is = null;

        try {
            is = url.openStream();
            Properties props = new Properties();
            props.load(url.openStream());
            return props;
        } catch (IOException e) {
            throw new BrixException("Could not read properties at classpath resource: " + resource, e);
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    LOG.error("error closing property input stream.", e);
                }
            }
        }
    }

    /**
     * Merge mode
     * 
     * @author igor.vaynberg
     * 
     */
    public static enum MergeMode {
        OVERRIDE_ONLY, MERGE
    }

    /**
     * Merges multiple {@link Properties} instances into one
     * 
     * @param mode
     *            merge mode
     * @param sources
     *            properties to merge
     * @return new instance of {@link Properties} containing merged values
     */
    public static Properties merge(MergeMode mode, Properties... sources) {
        Properties props = new Properties();

        for (int i = 0; i < sources.length; i++) {
            final Properties source = sources[i];
            for (Entry<Object, Object> prop : source.entrySet()) {
                final boolean exists = props.containsKey(prop.getKey());
                boolean set = false;
                switch (mode) {
                case MERGE:
                    set = true;
                    break;
                case OVERRIDE_ONLY:
                    set = exists;
                    break;
                default:
                    set = false;
                    break;
                }
                if (set || i == 0) {
                    props.put(prop.getKey(), prop.getValue());
                }
            }
        }
        return props;
    }
}