PropertyUtils.java

/*
 *  This file is part of the Heritrix web crawler (crawler.archive.org).
 *
 *  Licensed to the Internet Archive (IA) by one or more individual 
 *  contributors. 
 *
 *  The IA 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 org.archive.util;

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

import org.apache.commons.lang.StringUtils;

/**
 * Utilities for dealing with Java Properties (incl. System Properties)
 * 
 * @contributor stack
 * @contributor gojomo
 * @version $Date$ $Revision$
 */
public class PropertyUtils {
    /***
     * @param key Property key.
     * @return Named property or null if the property is null or empty.
     */
    public static String getPropertyOrNull(final String key) {
        String value = System.getProperty(key);
        return (value == null || value.length() <= 0)? null: value;
    }

    /***
     * @param key Property key.
     * @return Boolean value or false if null or unreadable.
     */
    public static boolean getBooleanProperty(final String key) {
        return (getPropertyOrNull(key) == null)?
                false: Boolean.valueOf(getPropertyOrNull(key)).booleanValue();
    }   
    
    /**
     * @param key Key to use looking up system property.
     * @param fallback If no value found for passed <code>key</code>, return
     * <code>fallback</code>.
     * @return Value of property or <code>fallback</code>.
     */
    public static int getIntProperty(final String key, final int fallback) {
        return getPropertyOrNull(key) == null?
                fallback: Integer.parseInt(getPropertyOrNull(key));
    }
    
    /**
     * Given a string which may contain expressions of the form 
     * ${key}, replace each expression with the value corresponding to the
     * given key in System Properties. If no value is present, 
     * the expression is replaced with the empty-string. 
     * 
     * @param original String
     * @param properties Properties to try in order; first value found (if any) is used
     * @return modified String
     */
    public static String interpolateWithProperties(String original) {
        return interpolateWithProperties(original,System.getProperties());
    }

    protected static String propRefPattern = "\\$\\{([^{}]+)\\}";
    
    /**
     * Given a string which may contain expressions of the form 
     * ${key}, replace each expression with the value corresponding to the
     * given key in the supplied Properties instance. If no value is present, 
     * the expression is replaced with the empty-string. 
     * 
     * @param original String
     * @param props Properties to try in order; first value found (if any) is used
     * @return modified String
     */
    public static String interpolateWithProperties(String original,
            Properties... props) {
        String result = original;
        // cap number of interpolations as guard against unending loop
        inter: for(int i =0; i < original.length()*2; i++) {
            Matcher m = TextUtils.getMatcher(propRefPattern, result);
            while(m.find()) {
                String key = m.group(1); 
                String value = "";
                for(Properties properties : props) {
                    value = properties.getProperty(key, "");
                    if(StringUtils.isNotEmpty(value)) {
                        break;
                    }
                }
                result = result.substring(0,m.start()) 
                            + value
                            + result.substring(m.end());
                continue inter;
            }
            // we only hit here if there were no interpolations last while loop
            break;
        }
        return result; 
    }
}