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    }