    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}