    001// Copyright 2007, 2008, 2009, 2010 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.services;
    016
    017import org.apache.tapestry5.ComponentResources;
    018import org.apache.tapestry5.ioc.annotations.UsesMappedConfiguration;
    019
    020/**
    021 * Used to lookup meta data concerning a particular component. The primary source of meta data is the meta data defined
    022 * for the component, accessed via {@link org.apache.tapestry5.model.ComponentModel#getMeta(String)}. This includes meta
    023 * data defined by base classes. When meta-data for a particular component can not be found, a search works up the
    024 * containment hierarchy (to the component's container, and the container's container, and so on). If <em>that</em>
    025 * proves unfruitful, a system of defaults is provided by configuration and matched against the containing page's
    026 * logical name.
    027 * <p/>
    028 * Finally, if no metadata is available, then {@link org.apache.tapestry5.ioc.services.SymbolSource#valueForSymbol(String)}
    029 * is used to obtain a value. Generally speaking, if you are going to use this service to look up meta data, your should
    030 * also make a contribution to the FactoryDefaults service; otherwise, you risk a runtime exception if a meta-data key
    031 * can not be resolved.
    032 */
    033@UsesMappedConfiguration(String.class)
    034public interface MetaDataLocator
    035{
    036    /**
    037     * Searches for the value for the corresponding key.  The value, if located, will have symbols expanded, and will be
    038     * type coerced to the desired type.
    039     *
    040     * @param key       the key used to locate the meta data (case insensitive)
    041     * @param resources the resources of the initial component used in the search
    042     * @return the value if found (in the component, the component's container, etc. or via a folder default)
    043     * @throws RuntimeException if the value for the key is not present as meta data of the component, as an override,
    044     *                          or as a symbol
    045     */
    046    <T> T findMeta(String key, ComponentResources resources, Class<T> expectedType);
    047
    048    /**
    049     * Searches for the value for the corresponding key for a particular page name (the page will <em>not</em> be
    050     * loaded).  The value, if located, will have symbols expanded, and will be type coerced to the desired type.
    051     *
    052     * @param key      the key used to locate the meta data (case insensitive)
    053     * @param pageName the name of the page to search
    054     * @return the value if found
    055     * @throws RuntimeException if the value for the key is not present as meta data of the page, as an override, or as
    056     *                          a symbol
    057     */
    058    <T> T findMeta(String key, String pageName, Class<T> expectedType);
    059}