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    
025    public interface IPropertySource
026    {
027        /**
028         *  Returns the value for a given property, or null if the
029         *  source does not provide a value for the named property.
030         *  Implementations of IPropertySource may use delegation
031         *  to resolve the value (that is, if one property source returns null,
032         *  it may forward the request to another source).
033         * 
034         **/
035        
036        public String getPropertyValue(String propertyName);
037    }