    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
    015    package org.apache.tapestry5.services;
    016
    017    import org.apache.tapestry5.ComponentResources;
    018    import 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)
    034    public 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    }