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.services;
016    
017    import org.apache.tapestry.IEngine;
018    
019    /**
020     * Service responsible for obtaining instances of
021     * {@link org.apache.tapestry.IEngine} to service the current request. An engine
022     * service may be retrieved from a pool, or extracted from the HttpSession.
023     * After the request is processed, the engine is re-stored into the HttpSession
024     * (if stateful) or back into the pool (if not stateful).
025     * 
026     * @author Howard Lewis Ship
027     * @since 4.0
028     */
029    public interface EngineManager
030    {
031    
032        /**
033         * Locates or creates an engine instance for the current request.
034         */
035        IEngine getEngineInstance();
036    
037        /**
038         * Store the engine back at the end of the current request.
039         */
040    
041        void storeEngineInstance(IEngine engine);
042    }