001// Copyright 2006, 2008, 2013 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
015package org.apache.tapestry5.ioc.services;
016
017import 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 * @see FactoryDefaults
026 * @see ApplicationDefaults
027 */
028@UsesMappedConfiguration(String.class)
029public interface SymbolProvider
030{
031    /**
032     * Returns the value for the symbol, or null if this provider can not provide a value. The value itself may contain
033     * symbols that will be recursively expanded.
034     *
035     * @param symbolName
036     * @return the value or null
037     */
038    String valueForSymbol(String symbolName);
039}