PropertyResolver.java

package org.codehaus.mojo.properties;

/*
 * 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.
 */

import java.util.*;

class PropertyResolver {

    /**
     * Retrieves a property value, replacing values like ${token}
     * using the Properties to look them up.
     * Shamelessly adapted from:
     * http://maven.apache.org/plugins/maven-war-plugin/xref/org/apache/maven/plugin/war/PropertyUtils.html
     *
     * It will leave unresolved properties alone, trying for System
     * properties, and environment variables and implements reparsing
     * (in the case that the value of a property contains a key), and will
     * not loop endlessly on a pair like test = ${test}
     *
     * @param key           property key
     * @param properties           project properties
     * @param environment environment variables
     * @return resolved property value
     * @throws IllegalArgumentException when properties are circularly defined
     */
    public String getPropertyValue( String key, Properties properties, Properties environment )
    {
        String value = properties.getProperty(key);

        ExpansionBuffer buffer = new ExpansionBuffer(value);

        CircularDefinitionPreventer circularDefinitionPreventer =
                new CircularDefinitionPreventer().visited( key, value);

        while ( buffer.hasMoreLegalPlaceholders() )
        {
            String newKey = buffer.extractPropertyKey();
            String newValue = fromPropertiesThenSystemThenEnvironment( newKey, properties, environment );

            circularDefinitionPreventer.visited(newKey, newValue);

            buffer.add( newKey, newValue );
        }

        return buffer.toString();
    }

    private String fromPropertiesThenSystemThenEnvironment(String key, Properties properties, Properties environment)
    {
        String value = properties.getProperty( key );

        // try global environment
        if ( value == null )
        {
            value = System.getProperty( key );
        }

        // try environment variable
        if ( value == null && key.startsWith( "env." ) && environment != null )
        {
            value = environment.getProperty( key.substring( 4 ) );
        }

        return value;
    }
}