    001    package 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
    024    import java.io.IOException;
    025
    026    import org.apache.turbine.util.TurbineException;
    027
    028    /**
    029     * <p>A <b>Valve</b> is a request processing component.  A series of
    030     * Valves are generally associated with each other into a Pipeline.
    031     * The detailed contract for a Valve is included in the description of
    032     * the <code>invoke()</code> method below.</p>
    033     *
    034     * <b>HISTORICAL NOTE</b>:  The "Valve" name was assigned to this concept
    035     * because a valve is what you use in a real world pipeline to control and/or
    036     * modify flows through it.
    037     *
    038     * @author Craig R. McClanahan
    039     * @author Gunnar Rjnning
    040     * @author Peter Donald
    041     * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
    042     *
    043     * @see #invoke(RunData, ValveContext)
    044     */
    045    public interface Valve
    046    {
    047        /**
    048         * <p>Perform request processing as required by this Valve.</p>
    049         *
    050         * <p>An individual Valve <b>MAY</b> perform the following actions, in
    051         * the specified order:</p>
    052         * <ul>
    053         * <li>Examine and/or modify the properties of the specified Request and
    054         *     Response.
    055         * <li>Examine the properties of the specified Request, completely generate
    056         *     the corresponding Response, and return control to the caller.
    057         * <li>Examine the properties of the specified Request and Response, wrap
    058         *     either or both of these objects to supplement their functionality,
    059         *     and pass them on.
    060         * <li>If the corresponding Response was not generated (and control was not
    061         *     returned, call the next Valve in the pipeline (if there is one) by
    062         *     executing <code>context.invokeNext()</code>.
    063         * <li>Examine, but not modify, the properties of the resulting Response
    064         *     (which was created by a subsequently invoked Valve via a
    065         *     call to <code>context.invokeNext()</code>).
    066         * </ul>
    067         *
    068         * <p>A Valve <b>MUST NOT</b> do any of the following things:</p>
    069         * <ul>
    070         * <li>Change request properties that have already been used to direct
    071         *     the flow of processing control for this request.
    072         * <li>Create a completed Response <strong>AND</strong> pass this
    073         *     Request and Response on to the next Valve in the pipeline.
    074         * <li>Consume bytes from the input stream associated with the Request,
    075         *     unless it is completely generating the response, or wrapping the
    076         *     request before passing it on.
    077         * <li>Modify the HTTP headers included with the Response after the
    078         *     <code>invokeNext()</code> method has returned.
    079         * <li>Perform any actions on the output stream associated with the
    080         *     specified Response after the <code>invokeNext()</code> method has
    081         *     returned.
    082         * </ul>
    083         *
    084         * @param data The run-time information, including the servlet
    085         * request and response we are processing.
    086         * @param context The valve context used to invoke the next valve
    087         *  in the current processing pipeline
    088         *
    089         * @exception IOException Thrown by a subsequent Valve.
    090         * @exception TurbineException Thrown by a subsequent Valve.
    091         */
    092        public void invoke(PipelineData data, ValveContext context)
    093            throws IOException, TurbineException;
    094
    095        /**
    096         * Initialize the valve before using in a pipeline.
    097         */
    098        public void initialize()
    099            throws Exception;
    100    }