001    // Copyright 2006, 2008 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.tapestry5.ioc.services;
016    
017    import org.apache.tapestry5.ioc.annotations.UsesMappedConfiguration;
018    
019    /**
020     * A provider of values for symbols, used by the {@link org.apache.tapestry5.ioc.services.SymbolSource} service.
021     * <p/>
022     * This is the service interface for the FactoryDefaults and ApplicationDefaults services; each of these takes a
023     * configuration mapping symbols to their values.
024     */
025    @UsesMappedConfiguration(String.class)
026    public interface SymbolProvider
027    {
028        /**
029         * Returns the value for the symbol, or null if this provider can not provide a value. The value itself may contain
030         * symbols that will be recursively expanded.
031         *
032         * @param symbolName
033         * @return the value or null
034         */
035        String valueForSymbol(String symbolName);
036    }