1 /*
2 * Copyright 2002-2007 the original author or authors.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package org.springframework.web.servlet.mvc;
18
19 import javax.servlet.http.HttpServletRequest;
20 import javax.servlet.http.HttpServletResponse;
21 import javax.servlet.http.HttpSession;
22
23 import org.springframework.web.servlet.ModelAndView;
24 import org.springframework.web.servlet.support.WebContentGenerator;
25 import org.springframework.web.util.WebUtils;
26
27 /**
28 * <p>Convenient superclass for controller implementations, using the Template
29 * Method design pattern.</p>
30 *
31 * <p>As stated in the {@link org.springframework.web.servlet.mvc.Controller Controller}
32 * interface, a lot of functionality is already provided by certain abstract
33 * base controllers. The AbstractController is one of the most important
34 * abstract base controller providing basic features such as the generation
35 * of caching headers and the enabling or disabling of
36 * supported methods (GET/POST).</p>
37 *
38 * <p><b><a name="workflow">Workflow
39 * (<a href="Controller.html#workflow">and that defined by interface</a>):</b><br>
40 * <ol>
41 * <li>{@link #handleRequest(HttpServletRequest,HttpServletResponse) handleRequest()}
42 * will be called by the DispatcherServlet</li>
43 * <li>Inspection of supported methods (ServletException if request method
44 * is not support)</li>
45 * <li>If session is required, try to get it (ServletException if not found)</li>
46 * <li>Set caching headers if needed according to cacheSeconds propery</li>
47 * <li>Call abstract method {@link #handleRequestInternal(HttpServletRequest,HttpServletResponse) handleRequestInternal()}
48 * (optionally synchronizing around the call on the HttpSession),
49 * which should be implemented by extending classes to provide actual
50 * functionality to return {@link org.springframework.web.servlet.ModelAndView ModelAndView} objects.</li>
51 * </ol>
52 * </p>
53 *
54 * <p><b><a name="config">Exposed configuration properties</a>
55 * (<a href="Controller.html#config">and those defined by interface</a>):</b><br>
56 * <table border="1">
57 * <tr>
58 * <td><b>name</b></th>
59 * <td><b>default</b></td>
60 * <td><b>description</b></td>
61 * </tr>
62 * <tr>
63 * <td>supportedMethods</td>
64 * <td>GET,POST</td>
65 * <td>comma-separated (CSV) list of methods supported by this controller,
66 * such as GET, POST and PUT</td>
67 * </tr>
68 * <tr>
69 * <td>requireSession</td>
70 * <td>false</td>
71 * <td>whether a session should be required for requests to be able to
72 * be handled by this controller. This ensures that derived controller
73 * can - without fear of null pointers - call request.getSession() to
74 * retrieve a session. If no session can be found while processing
75 * the request, a ServletException will be thrown</td>
76 * </tr>
77 * <tr>
78 * <td>cacheSeconds</td>
79 * <td>-1</td>
80 * <td>indicates the amount of seconds to include in the cache header
81 * for the response following on this request. 0 (zero) will include
82 * headers for no caching at all, -1 (the default) will not generate
83 * <i>any headers</i> and any positive number will generate headers
84 * that state the amount indicated as seconds to cache the content</td>
85 * </tr>
86 * <tr>
87 * <td>synchronizeOnSession</td>
88 * <td>false</td>
89 * <td>whether the call to <code>handleRequestInternal</code> should be
90 * synchronized around the HttpSession, to serialize invocations
91 * from the same client. No effect if there is no HttpSession.
92 * </td>
93 * </tr>
94 * </table>
95 *
96 * @author Rod Johnson
97 * @author Juergen Hoeller
98 * @see WebContentInterceptor
99 */
100 public abstract class AbstractController extends WebContentGenerator implements Controller {
101
102 private boolean synchronizeOnSession = false;
103
104
105 /**
106 * Set if controller execution should be synchronized on the session,
107 * to serialize parallel invocations from the same client.
108 * <p>More specifically, the execution of the <code>handleRequestInternal</code>
109 * method will get synchronized if this flag is "true". The best available
110 * session mutex will be used for the synchronization; ideally, this will
111 * be a mutex exposed by HttpSessionMutexListener.
112 * <p>The session mutex is guaranteed to be the same object during
113 * the entire lifetime of the session, available under the key defined
114 * by the <code>SESSION_MUTEX_ATTRIBUTE</code> constant. It serves as a
115 * safe reference to synchronize on for locking on the current session.
116 * <p>In many cases, the HttpSession reference itself is a safe mutex
117 * as well, since it will always be the same object reference for the
118 * same active logical session. However, this is not guaranteed across
119 * different servlet containers; the only 100% safe way is a session mutex.
120 * @see org.springframework.web.servlet.mvc.AbstractController#handleRequestInternal
121 * @see org.springframework.web.util.HttpSessionMutexListener
122 * @see org.springframework.web.util.WebUtils#getSessionMutex(javax.servlet.http.HttpSession)
123 */
124 public final void setSynchronizeOnSession(boolean synchronizeOnSession) {
125 this.synchronizeOnSession = synchronizeOnSession;
126 }
127
128 /**
129 * Return whether controller execution should be synchronized on the session.
130 */
131 public final boolean isSynchronizeOnSession() {
132 return this.synchronizeOnSession;
133 }
134
135
136 public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
137 throws Exception {
138
139 // Delegate to WebContentGenerator for checking and preparing.
140 checkAndPrepare(request, response, this instanceof LastModified);
141
142 // Execute handleRequestInternal in synchronized block if required.
143 if (this.synchronizeOnSession) {
144 HttpSession session = request.getSession(false);
145 if (session != null) {
146 Object mutex = WebUtils.getSessionMutex(session);
147 synchronized (mutex) {
148 return handleRequestInternal(request, response);
149 }
150 }
151 }
152
153 return handleRequestInternal(request, response);
154 }
155
156 /**
157 * Template method. Subclasses must implement this.
158 * The contract is the same as for <code>handleRequest</code>.
159 * @see #handleRequest
160 */
161 protected abstract ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
162 throws Exception;
163
164 }
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