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 @FunctionalInterface
46 public interface Valve
47 {
48 /**
49 * <p>Perform request processing as required by this Valve.</p>
50 *
51 * <p>An individual Valve <b>MAY</b> perform the following actions, in
52 * the specified order:</p>
53 * <ul>
54 * <li>Examine and/or modify the properties of the specified Request and
55 * Response.
56 * <li>Examine the properties of the specified Request, completely generate
57 * the corresponding Response, and return control to the caller.
58 * <li>Examine the properties of the specified Request and Response, wrap
59 * either or both of these objects to supplement their functionality,
60 * and pass them on.
61 * <li>If the corresponding Response was not generated (and control was not
62 * returned, call the next Valve in the pipeline (if there is one) by
63 * executing <code>context.invokeNext()</code>.
64 * <li>Examine, but not modify, the properties of the resulting Response
65 * (which was created by a subsequently invoked Valve via a
66 * call to <code>context.invokeNext()</code>).
67 * </ul>
68 *
69 * <p>A Valve <b>MUST NOT</b> do any of the following things:</p>
70 * <ul>
71 * <li>Change request properties that have already been used to direct
72 * the flow of processing control for this request.
73 * <li>Create a completed Response <strong>AND</strong> pass this
74 * Request and Response on to the next Valve in the pipeline.
75 * <li>Consume bytes from the input stream associated with the Request,
76 * unless it is completely generating the response, or wrapping the
77 * request before passing it on.
78 * <li>Modify the HTTP headers included with the Response after the
79 * <code>invokeNext()</code> method has returned.
80 * <li>Perform any actions on the output stream associated with the
81 * specified Response after the <code>invokeNext()</code> method has
82 * returned.
83 * </ul>
84 *
85 * @param pipelineData The run-time information, including the servlet
86 * request and response we are processing.
87 * @param context The valve context used to invoke the next valve
88 * in the current processing pipeline
89 *
90 * @throws IOException Thrown by a subsequent Valve.
91 * @throws TurbineException Thrown by a subsequent Valve.
92 */
93 void invoke(PipelineData pipelineData, ValveContext context)
94 throws IOException, TurbineException;
95
96 /**
97 * Initialize the valve before using in a pipeline.
98 * @throws Exception if initialization fails
99 */
100 default void initialize() throws Exception
101 {
102 // empty
103 }
104 }