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 }