001    // Copyright 2004, 2005 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry.engine;
016    
017    /**
018     * A source for configuration properties.
019     * 
020     * @author Howard Lewis Ship
021     * @since 2.3
022     */
023    
024    public interface IPropertySource
025    {
026    
027        /**
028         * Returns the value for a given property, or null if the source does not
029         * provide a value for the named property. Implementations of
030         * IPropertySource may use delegation to resolve the value (that is, if one
031         * property source returns null, it may forward the request to another
032         * source).
033         *
034         * @param propertyName
035         *          Name of the property to get.
036         * 
037         * @return Value of property or null if none found.
038         */
039    
040        String getPropertyValue(String propertyName);
041    }