    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.services;
    014
    015import org.apache.tapestry5.ComponentResources;
    016import org.apache.tapestry5.ioc.annotations.UsesMappedConfiguration;
    017
    018/**
    019 * Used to lookup meta data concerning a particular component. The primary source of meta data is the meta data defined
    020 * for the component, accessed via {@link org.apache.tapestry5.model.ComponentModel#getMeta(String)}. This includes meta
    021 * data defined by base classes. When meta-data for a particular component can not be found, a search works up the
    022 * containment hierarchy (to the component's container, and the container's container, and so on). If <em>that</em>
    023 * proves unfruitful, a system of defaults is provided by configuration and matched against the containing page's
    024 * logical name.
    025 *
    026 * Finally, if no metadata is available, then {@link org.apache.tapestry5.ioc.services.SymbolSource#valueForSymbol(String)}
    027 * is used to obtain a value. Generally speaking, if you are going to use this service to look up meta data, your should
    028 * also make a contribution to the FactoryDefaults service; otherwise, you risk a runtime exception if a meta-data key
    029 * can not be resolved.
    030 */
    031@UsesMappedConfiguration(String.class)
    032public interface MetaDataLocator
    033{
    034    /**
    035     * Searches for the value for the corresponding key.  The value, if located, will have symbols expanded, and will be
    036     * type coerced to the desired type.
    037     *
    038     * @param key       the key used to locate the meta data (case insensitive)
    039     * @param resources the resources of the initial component used in the search
    040     * @return the value if found (in the component, the component's container, etc. or via a folder default)
    041     * @throws RuntimeException if the value for the key is not present as meta data of the component, as an override,
    042     *                          or as a symbol
    043     */
    044    <T> T findMeta(String key, ComponentResources resources, Class<T> expectedType);
    045
    046    /**
    047     * Searches for the value for the corresponding key for a particular page name (the page will <em>not</em> be
    048     * loaded).  The value, if located, will have symbols expanded, and will be type coerced to the desired type.
    049     *
    050     * @param key      the key used to locate the meta data (case insensitive)
    051     * @param pageName the name of the page to search
    052     * @return the value if found
    053     * @throws RuntimeException if the value for the key is not present as meta data of the page, as an override, or as
    054     *                          a symbol
    055     */
    056    <T> T findMeta(String key, String pageName, Class<T> expectedType);
    057}