    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}