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 }