001    // Copyright 2004, 2005 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.tapestry.engine;
016    
017    import org.apache.hivemind.ClassResolver;
018    import org.apache.tapestry.IPage;
019    import org.apache.tapestry.IRequestCycle;
020    
021    /**
022     * Abstracts the process of loading pages from thier specifications as well as pooling of pages once
023     * loaded.
024     * <p>
025     * If the required page is not available, a page source may use an instance of {@link IPageLoader}
026     * to actually load the page (and all of its nested components).
027     * 
028     * @author Howard Lewis Ship
029     */
030    
031    public interface IPageSource
032    {
033        /**
034         * Gets a given page for the engine. This may involve using a previously loaded page from a pool
035         * of available pages, or the page may be loaded as needed.
036         * 
037         * @param cycle
038         *            the current request cycle
039         * @param pageName
040         *            the name of the page. May be qualified with a library id prefix, which may even be
041         *            nested. Unqualified names are searched for extensively in the application
042         *            namespace, and then in the framework namespace.
043         * @return The loaded page.
044         * 
045         * @throws org.apache.tapestry.PageNotFoundException
046         *             if pageName can't be resolved to a page specification (from which a page instance
047         *             can be generated).
048         * @see org.apache.tapestry.resolver.PageSpecificationResolver#resolve(IRequestCycle, String)
049         */
050    
051        IPage getPage(IRequestCycle cycle, String pageName);
052    
053        /**
054         * Invoked after the engine is done with the page (typically, after the response to the client
055         * has been sent). The page is returned to the pool for later reuse.
056         *
057         * @param page The page to release.
058         */
059        void releasePage(IPage page);
060    
061        /**
062         * Gets the class resolver used to load all pages / page components.
063         *
064         * @return {@link ClassResolver} instance used to load classes. 
065         */
066    
067        ClassResolver getClassResolver();
068    }