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    1   package org.apache.turbine.pipeline;
    2
    3
    4   /*
    5    * Licensed to the Apache Software Foundation (ASF) under one
    6    * or more contributor license agreements.  See the NOTICE file
    7    * distributed with this work for additional information
    8    * regarding copyright ownership.  The ASF licenses this file
    9    * to you under the Apache License, Version 2.0 (the
    10   * "License"); you may not use this file except in compliance
    11   * with the License.  You may obtain a copy of the License at
    12   *
    13   *   http://www.apache.org/licenses/LICENSE-2.0
    14   *
    15   * Unless required by applicable law or agreed to in writing,
    16   * software distributed under the License is distributed on an
    17   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    18   * KIND, either express or implied.  See the License for the
    19   * specific language governing permissions and limitations
    20   * under the License.
    21   */
    22
    23
    24  import java.io.IOException;
    25
    26  import org.apache.turbine.util.TurbineException;
    27
    28  /**
    29   * The idea of a pipeline is being taken from Catalina
    30   * in its entirety :-)
    31   *
    32   * I would like to take the idea further and implement
    33   * Valves instead of hardcoding particular methods
    34   * in a pipeline.
    35   *
    36   * It would be more flexible to specify Valves for
    37   * a pipeline in an XML file (we can also rip off the
    38   * digester rules from T4) and have invoke() as part
    39   * of the interface.
    40   *
    41   * So a set of Valves would be added to the pipeline
    42   * and the pipeline would 'invoke' each valve. In the
    43   * case Turbine each Valve would produce some output
    44   * to be sent out the pipe. I think with another days
    45   * work this can be fully working. The first pipeline
    46   * to be fully implemented will the ClassicPipeline
    47   * will emulate the Turbine 2.1 way of doing things.
    48   *
    49   * @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a>
    50   * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
    51   * @author <a href="mailto:peter@courcoux.biz">Peter Courcoux</a>
    52   */
    53  public interface Pipeline
    54  {
    55      /**
    56       * Initializes this instance.  Called once by the Turbine servlet.
    57       */
    58      public void initialize()
    59          throws Exception;
    60
    61      /**
    62       * <p>Add a new Valve to the end of the pipeline.</p>
    63       *
    64       * @param valve Valve to be added.
    65       *
    66       * @exception IllegalStateException If the pipeline has not been
    67       * initialized.
    68       */
    69      public void addValve(Valve valve);
    70
    71      /**
    72       * Return the set of all Valves in the pipeline.  If there are no
    73       * such Valves, a zero-length array is returned.
    74       *
    75       * @return An array of valves.
    76       */
    77      public Valve[] getValves();
    78
    79      /**
    80       * <p>Cause the specified request and response to be processed by
    81       * the sequence of Valves associated with this pipeline, until one
    82       * of these Valves decides to end the processing.</p>
    83       *
    84       * <p>The implementation must ensure that multiple simultaneous
    85       * requests (on different threads) can be processed through the
    86       * same Pipeline without interfering with each other's control
    87       * flow.</p>
    88       *
    89       * @param data The run-time information, including the servlet
    90       * request and response we are processing.
    91       *
    92       * @exception IOException an input/output error occurred.
    93       */
    94      public void invoke(PipelineData data)
    95          throws TurbineException, IOException;
    96
    97      /**
    98       * Remove the specified Valve from the pipeline, if it is found;
    99       * otherwise, do nothing.
    100      *
    101      * @param valve Valve to be removed.
    102      */
    103     public void removeValve(Valve valve);
    104 }