001// Licensed under the Apache License, Version 2.0 (the "License");
002// you may not use this file except in compliance with the License.
003// You may obtain a copy of the License at
004//
005//     http://www.apache.org/licenses/LICENSE-2.0
006//
007// Unless required by applicable law or agreed to in writing, software
008// distributed under the License is distributed on an "AS IS" BASIS,
009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
010// See the License for the specific language governing permissions and
011// limitations under the License.
012
013package org.apache.tapestry5.ioc.services;
014
015import org.apache.tapestry5.ioc.annotations.UsesMappedConfiguration;
016
017/**
018 * A provider of values for symbols, used by the {@link org.apache.tapestry5.ioc.services.SymbolSource} service.
019 *
020 * This is the service interface for the FactoryDefaults and ApplicationDefaults services; each of these takes a
021 * configuration mapping symbols to their values.
022 *
023 * @see FactoryDefaults
024 * @see ApplicationDefaults
025 */
026@UsesMappedConfiguration(String.class)
027public interface SymbolProvider
028{
029    /**
030     * Returns the value for the symbol, or null if this provider can not provide a value. The value itself may contain
031     * symbols that will be recursively expanded.
032     *
033     * @param symbolName
034     * @return the value or null
035     */
036    String valueForSymbol(String symbolName);
037}