Util.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 org.liveSense.server.i18n.loader;

import java.util.Dictionary;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

public class Util
{
    private static final String DELIM_START = "${";
    private static final String DELIM_STOP = "}";

    private static final String CHECKSUM_SUFFIX = ".checksum";

    /**
     * Perform substitution on a property set
     *
     * @param properties the property set to perform substitution on
     */
    public static void performSubstitution(Dictionary properties)
    {
        for (Enumeration e = properties.keys(); e.hasMoreElements(); )
        {
            String name = (String) e.nextElement();
            Object value = properties.get(name);
            properties.put(name,
                value instanceof String
                    ? Util.substVars((String) value, name, null, properties)
                    : value);
        }
    }

    /**
     * <p>
     * This method performs property variable substitution on the
     * specified value. If the specified value contains the syntax
     * <tt>${<prop-name>}</tt>, where <tt><prop-name></tt>
     * refers to either a configuration property or a system property,
     * then the corresponding property value is substituted for the variable
     * placeholder. Multiple variable placeholders may exist in the
     * specified value as well as nested variable placeholders, which
     * are substituted from inner most to outer most. Configuration
     * properties override system properties.
     * </p>
     * @param val The string on which to perform property substitution.
     * @param currentKey The key of the property being evaluated used to
     *        detect cycles.
     * @param cycleMap Map of variable references used to detect nested cycles.
     * @param configProps Set of configuration properties.
     * @return The value of the specified string after system property substitution.
     * @throws IllegalArgumentException If there was a syntax error in the
     *         property placeholder syntax or a recursive variable reference.
     **/
    public static String substVars(String val, String currentKey, Map cycleMap, Dictionary configProps)
        throws IllegalArgumentException
    {
        if (cycleMap == null)
        {
            cycleMap = new HashMap();
        }

        // Put the current key in the cycle map.
        cycleMap.put(currentKey, currentKey);

        // Assume we have a value that is something like:
        // "leading ${foo.${bar}} middle ${baz} trailing"

        // Find the first ending '}' variable delimiter, which
        // will correspond to the first deepest nested variable
        // placeholder.
        int stopDelim = val.indexOf(DELIM_STOP);

        // Find the matching starting "${" variable delimiter
        // by looping until we find a start delimiter that is
        // greater than the stop delimiter we have found.
        int startDelim = val.indexOf(DELIM_START);
        while (stopDelim >= 0)
        {
            int idx = val.indexOf(DELIM_START, startDelim + DELIM_START.length());
            if ((idx < 0) || (idx > stopDelim))
            {
                break;
            }
            else if (idx < stopDelim)
            {
                startDelim = idx;
            }
        }

        // If we do not have a start or stop delimiter, then just
        // return the existing value.
        if ((startDelim < 0) || (stopDelim < 0))
        {
            return val;
        }

        // At this point, we have found a variable placeholder so
        // we must perform a variable substitution on it.
        // Using the start and stop delimiter indices, extract
        // the first, deepest nested variable placeholder.
        String variable = val.substring(startDelim + DELIM_START.length(), stopDelim);

        // Verify that this is not a recursive variable reference.
        if (cycleMap.get(variable) != null)
        {
            throw new IllegalArgumentException("recursive variable reference: " + variable);
        }

        // Get the value of the deepest nested variable placeholder.
        // Try to configuration properties first.
        String substValue = (String) ((configProps != null) ? configProps.get(variable) : null);
        if (substValue == null)
        {
            // Ignore unknown property values.
            substValue = System.getProperty(variable, "");
        }

        // Remove the found variable from the cycle map, since
        // it may appear more than once in the value and we don't
        // want such situations to appear as a recursive reference.
        cycleMap.remove(variable);

        // Append the leading characters, the substituted value of
        // the variable, and the trailing characters to get the new
        // value.
        val = val.substring(0, startDelim) + substValue + val.substring(stopDelim + DELIM_STOP.length(), val.length());

        // Now perform substitution again, since there could still
        // be substitutions to make.
        val = substVars(val, currentKey, cycleMap, configProps);

        // Return the value.
        return val;
    }


}