001package org.apache.turbine.pipeline;
002
003
004/*
005 * Licensed to the Apache Software Foundation (ASF) under one
006 * or more contributor license agreements.  See the NOTICE file
007 * distributed with this work for additional information
008 * regarding copyright ownership.  The ASF licenses this file
009 * to you under the Apache License, Version 2.0 (the
010 * "License"); you may not use this file except in compliance
011 * with the License.  You may obtain a copy of the License at
012 *
013 *   http://www.apache.org/licenses/LICENSE-2.0
014 *
015 * Unless required by applicable law or agreed to in writing,
016 * software distributed under the License is distributed on an
017 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
018 * KIND, either express or implied.  See the License for the
019 * specific language governing permissions and limitations
020 * under the License.
021 */
022
023
024import java.io.IOException;
025
026import org.apache.turbine.util.TurbineException;
027
028/**
029 * The idea of a pipeline is being taken from Catalina
030 * in its entirety :-)
031 *
032 * I would like to take the idea further and implement
033 * Valves instead of hardcoding particular methods
034 * in a pipeline.
035 *
036 * It would be more flexible to specify Valves for
037 * a pipeline in an XML file (we can also rip off the
038 * digester rules from T4) and have invoke() as part
039 * of the interface.
040 *
041 * So a set of Valves would be added to the pipeline
042 * and the pipeline would 'invoke' each valve. In the
043 * case Turbine each Valve would produce some output
044 * to be sent out the pipe. I think with another days
045 * work this can be fully working. The first pipeline
046 * to be fully implemented will the ClassicPipeline
047 * will emulate the Turbine 2.1 way of doing things.
048 *
049 * @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a>
050 * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
051 * @author <a href="mailto:peter@courcoux.biz">Peter Courcoux</a>
052 */
053public interface Pipeline
054{
055    /**
056     * Initializes this instance.  Called once by the Turbine servlet.
057     * @throws Exception if the initialization fails
058     */
059    void initialize()
060        throws Exception;
061
062    /**
063     * <p>Add a new Valve to the end of the pipeline.</p>
064     *
065     * @param valve Valve to be added.
066     *
067     * @throws IllegalStateException If the pipeline has not been
068     * initialized.
069     */
070    void addValve(Valve valve);
071
072    /**
073     * Return the set of all Valves in the pipeline.  If there are no
074     * such Valves, a zero-length array is returned.
075     *
076     * @return An array of valves.
077     */
078    Valve[] getValves();
079
080    /**
081     * <p>Cause the specified request and response to be processed by
082     * the sequence of Valves associated with this pipeline, until one
083     * of these Valves decides to end the processing.</p>
084     *
085     * <p>The implementation must ensure that multiple simultaneous
086     * requests (on different threads) can be processed through the
087     * same Pipeline without interfering with each other's control
088     * flow.</p>
089     *
090     * @param pipelineData The run-time information, including the servlet
091     * request and response we are processing.
092     * @throws TurbineException if the invocation fails
093     * @throws IOException an input/output error occurred.
094     */
095    void invoke(PipelineData pipelineData)
096        throws TurbineException, IOException;
097
098    /**
099     * Remove the specified Valve from the pipeline, if it is found;
100     * otherwise, do nothing.
101     *
102     * @param valve Valve to be removed.
103     */
104    void removeValve(Valve valve);
105}