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 * <p>A <b>Valve</b> is a request processing component. A series of 30 * Valves are generally associated with each other into a Pipeline. 31 * The detailed contract for a Valve is included in the description of 32 * the <code>invoke()</code> method below.</p> 33 * 34 * <b>HISTORICAL NOTE</b>: The "Valve" name was assigned to this concept 35 * because a valve is what you use in a real world pipeline to control and/or 36 * modify flows through it. 37 * 38 * @author Craig R. McClanahan 39 * @author Gunnar Rjnning 40 * @author Peter Donald 41 * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a> 42 * 43 * @see #invoke(PipelineData, ValveContext) 44 */ 45 public interface Valve 46 { 47 /** 48 * <p>Perform request processing as required by this Valve.</p> 49 * 50 * <p>An individual Valve <b>MAY</b> perform the following actions, in 51 * the specified order:</p> 52 * <ul> 53 * <li>Examine and/or modify the properties of the specified Request and 54 * Response. 55 * <li>Examine the properties of the specified Request, completely generate 56 * the corresponding Response, and return control to the caller. 57 * <li>Examine the properties of the specified Request and Response, wrap 58 * either or both of these objects to supplement their functionality, 59 * and pass them on. 60 * <li>If the corresponding Response was not generated (and control was not 61 * returned, call the next Valve in the pipeline (if there is one) by 62 * executing <code>context.invokeNext()</code>. 63 * <li>Examine, but not modify, the properties of the resulting Response 64 * (which was created by a subsequently invoked Valve via a 65 * call to <code>context.invokeNext()</code>). 66 * </ul> 67 * 68 * <p>A Valve <b>MUST NOT</b> do any of the following things:</p> 69 * <ul> 70 * <li>Change request properties that have already been used to direct 71 * the flow of processing control for this request. 72 * <li>Create a completed Response <strong>AND</strong> pass this 73 * Request and Response on to the next Valve in the pipeline. 74 * <li>Consume bytes from the input stream associated with the Request, 75 * unless it is completely generating the response, or wrapping the 76 * request before passing it on. 77 * <li>Modify the HTTP headers included with the Response after the 78 * <code>invokeNext()</code> method has returned. 79 * <li>Perform any actions on the output stream associated with the 80 * specified Response after the <code>invokeNext()</code> method has 81 * returned. 82 * </ul> 83 * 84 * @param pipelineData The run-time information, including the servlet 85 * request and response we are processing. 86 * @param context The valve context used to invoke the next valve 87 * in the current processing pipeline 88 * 89 * @exception IOException Thrown by a subsequent Valve. 90 * @exception TurbineException Thrown by a subsequent Valve. 91 */ 92 public void invoke(PipelineData pipelineData, ValveContext context) 93 throws IOException, TurbineException; 94 95 /** 96 * Initialize the valve before using in a pipeline. 97 * @throws Exception if initialization fails 98 */ 99 public void initialize() 100 throws Exception; 101 }