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annotate src/org/eclipse/jetty/continuation/Continuation.java @ 934:fe461f7cfc8e
simplify AsyncContinuation
author | Franklin Schmidt <fschmidt@gmail.com> |
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date | Sun, 09 Oct 2016 21:03:00 -0600 |
parents | cd080b7bcf49 |
children | aa7dc1802d29 |
rev | line source |
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1 // |
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2 // ======================================================================== |
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3 // Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd. |
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4 // ------------------------------------------------------------------------ |
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5 // All rights reserved. This program and the accompanying materials |
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6 // are made available under the terms of the Eclipse Public License v1.0 |
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7 // and Apache License v2.0 which accompanies this distribution. |
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8 // |
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9 // The Eclipse Public License is available at |
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10 // http://www.eclipse.org/legal/epl-v10.html |
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11 // |
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12 // The Apache License v2.0 is available at |
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13 // http://www.opensource.org/licenses/apache2.0.php |
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14 // |
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15 // You may elect to redistribute this code under either of these licenses. |
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16 // ======================================================================== |
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17 // |
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18 |
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19 package org.eclipse.jetty.continuation; |
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20 |
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21 import javax.servlet.Filter; |
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22 import javax.servlet.FilterChain; |
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23 import javax.servlet.Servlet; |
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24 import javax.servlet.ServletRequest; |
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25 import javax.servlet.ServletResponse; |
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26 import javax.servlet.ServletResponseWrapper; |
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27 |
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28 /* ------------------------------------------------------------ */ |
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29 /** |
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30 * Continuation. |
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31 * |
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32 * A continuation is a mechanism by which a HTTP Request can be suspended and |
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33 * restarted after a timeout or an asynchronous event has occurred. |
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34 * <p> |
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35 * The continuation mechanism is a portable mechanism that will work |
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36 * asynchronously without additional configuration of all jetty-7, |
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37 * jetty-8 and Servlet 3.0 containers. With the addition of |
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38 * the {@link ContinuationFilter}, the mechanism will also work |
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39 * asynchronously on jetty-6 and non-asynchronously on any |
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40 * servlet 2.5 container. |
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41 * <p> |
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42 * The Continuation API is a simplification of the richer async API |
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43 * provided by the servlet-3.0 and an enhancement of the continuation |
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44 * API that was introduced with jetty-6. |
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45 * </p> |
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46 * <h1>Continuation Usage</h1> |
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47 * <p> |
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48 * A continuation object is obtained for a request by calling the |
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49 * factory method {@link ContinuationSupport#getContinuation(ServletRequest)}. |
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50 * The continuation type returned will depend on the servlet container |
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51 * being used. |
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52 * </p> |
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53 * <p> |
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54 * There are two distinct style of operation of the continuation API. |
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55 * </p> |
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56 * <h3>Suspend/Resume Usage</h3> |
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57 * <p>The suspend/resume style is used when a servlet and/or |
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58 * filter is used to generate the response after a asynchronous wait that is |
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59 * terminated by an asynchronous handler. |
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60 * </p> |
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61 * <pre> |
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62 * <b>Filter/Servlet:</b> |
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63 * // if we need to get asynchronous results |
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64 * Object results = request.getAttribute("results); |
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65 * if (results==null) |
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66 * { |
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67 * Continuation continuation = ContinuationSupport.getContinuation(request); |
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68 * continuation.suspend(); |
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69 * myAsyncHandler.register(continuation); |
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70 * return; // or continuation.undispatch(); |
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71 * } |
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72 * |
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73 * async wait ... |
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74 * |
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75 * <b>Async Handler:</b> |
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76 * // when the waited for event happens |
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77 * continuation.setAttribute("results",event); |
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78 * continuation.resume(); |
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79 * |
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80 * <b>Filter/Servlet:</b> |
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81 * // when the request is redispatched |
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82 * if (results==null) |
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83 * { |
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84 * ... // see above |
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85 * } |
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86 * else |
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87 * { |
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88 * response.getOutputStream().write(process(results)); |
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89 * } |
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90 * </pre> |
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91 * <h3>Suspend/Complete Usage</h3> |
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92 * <p> |
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93 * The suspend/complete style is used when an asynchronous handler is used to |
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94 * generate the response: |
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95 * </p> |
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96 * <pre> |
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97 * <b>Filter/Servlet:</b> |
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98 * // when we want to enter asynchronous mode |
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99 * Continuation continuation = ContinuationSupport.getContinuation(request); |
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100 * continuation.suspend(response); // response may be wrapped |
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101 * myAsyncHandler.register(continuation); |
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102 * return; // or continuation.undispatch(); |
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103 * |
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104 * <b>Wrapping Filter:</b> |
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105 * // any filter that had wrapped the response should be implemented like: |
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106 * try |
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107 * { |
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108 * chain.doFilter(request,wrappedResponse); |
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109 * } |
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110 * finally |
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111 * { |
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112 * if (!continuation.isResponseWrapped()) |
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113 * wrappedResponse.finish() |
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114 * else |
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115 * continuation.addContinuationListener(myCompleteListener) |
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116 * } |
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117 * |
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118 * async wait ... |
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119 * |
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120 * <b>Async Handler:</b> |
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121 * // when the async event happens |
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122 * continuation.getServletResponse().getOutputStream().write(process(event)); |
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123 * continuation.complete() |
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124 * </pre> |
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125 * |
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126 * <h1>Continuation Timeout</h1> |
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127 * <p> |
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128 * If a continuation is suspended, but neither {@link #complete()} or {@link #resume()} is |
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129 * called during the period set by {@link #setTimeout(long)}, then the continuation will |
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130 * expire and {@link #isExpired()} will return true. |
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131 * </p> |
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132 * <p> |
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133 * When a continuation expires, the {@link ContinuationListener#onTimeout(Continuation)} |
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134 * method is called on any {@link ContinuationListener} that has been registered via the |
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135 * {@link #addContinuationListener(ContinuationListener)} method. The onTimeout handlers |
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136 * may write a response and call {@link #complete()}. If {@link #complete()} is not called, |
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137 * then the container will redispatch the request as if {@link #resume()} had been called, |
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138 * except that {@link #isExpired()} will be true and {@link #isResumed()} will be false. |
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139 * </p> |
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140 * |
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141 * @see ContinuationSupport |
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142 * @see ContinuationListener |
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143 * |
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144 */ |
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145 public interface Continuation |
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146 { |
917 | 147 public final static String ATTRIBUTE = "org.eclipse.jetty.continuation"; |
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148 |
917 | 149 /* ------------------------------------------------------------ */ |
150 /** | |
151 * Set the continuation timeout. | |
152 * | |
153 * @param timeoutMs | |
154 * The time in milliseconds to wait before expiring this | |
155 * continuation after a call to {@link #suspend()} or {@link #suspend(ServletResponse)}. | |
156 * A timeout of <=0 means the continuation will never expire. | |
157 */ | |
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158 // void setTimeout(long timeoutMs); |
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159 |
917 | 160 /* ------------------------------------------------------------ */ |
161 /** | |
162 * Suspend the processing of the request and associated | |
163 * {@link ServletResponse}. | |
164 * | |
165 * <p> | |
166 * After this method has been called, the lifecycle of the request will be | |
167 * extended beyond the return to the container from the | |
168 * {@link Servlet#service(ServletRequest, ServletResponse)} method and | |
169 * {@link Filter#doFilter(ServletRequest, ServletResponse, FilterChain)} | |
170 * calls. When a suspended request is returned to the container after | |
171 * a dispatch, then the container will not commit the associated response | |
172 * (unless an exception other than {@link ContinuationThrowable} is thrown). | |
173 * </p> | |
174 * | |
175 * <p> | |
176 * When the thread calling the filter chain and/or servlet has returned to | |
177 * the container with a suspended request, the thread is freed for other | |
178 * tasks and the request is held until either: | |
179 * <ul> | |
180 * <li>a call to {@link #resume()}.</li> | |
181 * <li>a call to {@link #complete()}.</li> | |
182 * <li>the timeout expires.</li> | |
183 * </ul> | |
184 * <p> | |
185 * Typically suspend with no arguments is uses when a call to {@link #resume()} | |
186 * is expected. If a call to {@link #complete()} is expected, then the | |
187 * {@link #suspend(ServletResponse)} method should be used instead of this method. | |
188 * </p> | |
189 * | |
190 * @exception IllegalStateException | |
191 * If the request cannot be suspended | |
192 */ | |
193 // void suspend(); | |
194 | |
195 | |
196 /* ------------------------------------------------------------ */ | |
197 /** | |
198 * Suspend the processing of the request and associated | |
199 * {@link ServletResponse}. | |
200 * | |
201 * <p> | |
202 * After this method has been called, the lifecycle of the request will be | |
203 * extended beyond the return to the container from the | |
204 * {@link Servlet#service(ServletRequest, ServletResponse)} method and | |
205 * {@link Filter#doFilter(ServletRequest, ServletResponse, FilterChain)} | |
206 * calls. When a suspended request is returned to the container after | |
207 * a dispatch, then the container will not commit the associated response | |
208 * (unless an exception other than {@link ContinuationThrowable} is thrown). | |
209 * </p> | |
210 * <p> | |
211 * When the thread calling the filter chain and/or servlet has returned to | |
212 * the container with a suspended request, the thread is freed for other | |
213 * tasks and the request is held until either: | |
214 * <ul> | |
215 * <li>a call to {@link #resume()}.</li> | |
216 * <li>a call to {@link #complete()}.</li> | |
217 * <li>the timeout expires.</li> | |
218 * </ul> | |
219 * <p> | |
220 * Typically suspend with a response argument is uses when a call to {@link #complete()} | |
221 * is expected. If a call to {@link #resume()} is expected, then the | |
222 * {@link #suspend()} method should be used instead of this method. | |
223 * </p> | |
224 * <p> | |
225 * Filters that may wrap the response object should check {@link #isResponseWrapped()} | |
226 * to decide if they should destroy/finish the wrapper. If {@link #isResponseWrapped()} | |
227 * returns true, then the wrapped request has been passed to the asynchronous | |
228 * handler and the wrapper should not be destroyed/finished until after a call to | |
229 * {@link #complete()} (potentially using a {@link ContinuationListener#onComplete(Continuation)} | |
230 * listener). | |
231 * | |
232 * @param response The response to return via a call to {@link #getServletResponse()} | |
233 * @exception IllegalStateException | |
234 * If the request cannot be suspended | |
235 */ | |
236 // void suspend(ServletResponse response); | |
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237 |
917 | 238 /* ------------------------------------------------------------ */ |
239 /** | |
240 * Resume a suspended request. | |
241 * | |
242 * <p> | |
243 * This method can be called by any thread that has been passed a reference | |
244 * to a continuation. When called the request is redispatched to the | |
245 * normal filter chain and servlet processing with {@link #isInitial()} false. | |
246 * </p> | |
247 * <p> | |
248 * If resume is called before a suspended request is returned to the | |
249 * container (ie the thread that called {@link #suspend()} is still | |
250 * within the filter chain and/or servlet service method), then the resume | |
251 * does not take effect until the call to the filter chain and/or servlet | |
252 * returns to the container. In this case both {@link #isSuspended()} and | |
253 * {@link #isResumed()} return true. Multiple calls to resume are ignored. | |
254 * </p> | |
255 * <p> | |
256 * Typically resume() is used after a call to {@link #suspend()} with | |
257 * no arguments. The dispatch after a resume call will use the original | |
258 * request and response objects, even if {@link #suspend(ServletResponse)} | |
259 * had been passed a wrapped response. | |
260 * </p> | |
261 * | |
262 * @see #suspend() | |
263 * @exception IllegalStateException if the request is not suspended. | |
264 * | |
265 */ | |
923 | 266 // void resume(); |
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267 |
917 | 268 /* ------------------------------------------------------------ */ |
269 /** | |
270 * Complete a suspended request. | |
271 * | |
272 * <p> | |
273 * This method can be called by any thread that has been passed a reference | |
274 * to a suspended request. When a request is completed, the associated | |
275 * response object committed and flushed. The request is not redispatched. | |
276 * </p> | |
277 * | |
278 * <p> | |
279 * If complete is called before a suspended request is returned to the | |
280 * container (ie the thread that called {@link #suspend()} is still | |
281 * within the filter chain and/or servlet service method), then the complete | |
282 * does not take effect until the call to the filter chain and/or servlet | |
283 * returns to the container. In this case both {@link #isSuspended()} and | |
284 * {@link #isResumed()} return true. | |
285 * </p> | |
286 * | |
287 * <p> | |
288 * Typically resume() is used after a call to {@link #suspend(ServletResponse)} with | |
289 * a possibly wrapped response. The async handler should use the response | |
290 * provided by {@link #getServletResponse()} to write the response before | |
291 * calling {@link #complete()}. If the request was suspended with a | |
292 * call to {@link #suspend()} then no response object will be available via | |
293 * {@link #getServletResponse()}. | |
294 * </p> | |
295 * | |
296 * <p> | |
297 * Once complete has been called and any thread calling the filter chain | |
298 * and/or servlet chain has returned to the container, the request lifecycle | |
299 * is complete. The container is able to recycle request objects, so it is | |
300 * not valid hold a request or continuation reference after the end of the | |
301 * life cycle. | |
302 * | |
303 * @see #suspend() | |
304 * @exception IllegalStateException | |
305 * if the request is not suspended. | |
306 * | |
307 */ | |
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308 // void complete(); |
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309 |
917 | 310 /* ------------------------------------------------------------ */ |
311 /** | |
312 * @return true after {@link #suspend()} has been called and before the | |
313 * request has been redispatched due to being resumed, completed or | |
314 * timed out. | |
315 */ | |
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316 // boolean isSuspended(); |
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317 |
917 | 318 /* ------------------------------------------------------------ */ |
319 /** | |
320 * @return true if the request has been redispatched by a call to | |
321 * {@link #resume()}. Returns false after any subsequent call to | |
322 * suspend | |
323 */ | |
922 | 324 // boolean isResumed(); |
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325 |
917 | 326 /* ------------------------------------------------------------ */ |
327 /** | |
328 * @return true after a request has been redispatched as the result of a | |
329 * timeout. Returns false after any subsequent call to suspend. | |
330 */ | |
921 | 331 // boolean isExpired(); |
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332 |
917 | 333 /* ------------------------------------------------------------ */ |
334 /** | |
335 * @return true while the request is within the initial dispatch to the | |
336 * filter chain and/or servlet. Will return false once the calling | |
337 * thread has returned to the container after suspend has been | |
338 * called and during any subsequent redispatch. | |
339 */ | |
929 | 340 // boolean isInitial(); |
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341 |
917 | 342 /* ------------------------------------------------------------ */ |
343 /** | |
344 * Is the suspended response wrapped. | |
345 * <p> | |
346 * Filters that wrap the response object should check this method to | |
347 * determine if they should destroy/finish the wrapped response. If | |
348 * the request was suspended with a call to {@link #suspend(ServletResponse)} | |
349 * that passed the wrapped response, then the filter should register | |
350 * a {@link ContinuationListener} to destroy/finish the wrapped response | |
351 * during a call to {@link ContinuationListener#onComplete(Continuation)}. | |
352 * @return True if {@link #suspend(ServletResponse)} has been passed a | |
353 * {@link ServletResponseWrapper} instance. | |
354 */ | |
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355 // boolean isResponseWrapped(); |
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356 |
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357 |
917 | 358 /* ------------------------------------------------------------ */ |
359 /** | |
360 * Get the suspended response. | |
361 * @return the {@link ServletResponse} passed to {@link #suspend(ServletResponse)}. | |
362 */ | |
363 ServletResponse getServletResponse(); | |
364 | |
365 /* ------------------------------------------------------------ */ | |
366 /** | |
367 * Add a ContinuationListener. | |
368 * | |
369 * @param listener | |
370 */ | |
371 void addContinuationListener(ContinuationListener listener); | |
372 | |
373 /* ------------------------------------------------------------ */ | |
374 /** Set a request attribute. | |
375 * This method is a convenience method to call the {@link ServletRequest#setAttribute(String, Object)} | |
376 * method on the associated request object. | |
377 * This is a thread safe call and may be called by any thread. | |
378 * @param name the attribute name | |
379 * @param attribute the attribute value | |
380 */ | |
381 public void setAttribute(String name, Object attribute); | |
382 | |
383 /* ------------------------------------------------------------ */ | |
384 /** Get a request attribute. | |
385 * This method is a convenience method to call the {@link ServletRequest#getAttribute(String)} | |
386 * method on the associated request object. | |
387 * This is a thread safe call and may be called by any thread. | |
388 * @param name the attribute name | |
389 * @return the attribute value | |
390 */ | |
391 public Object getAttribute(String name); | |
392 | |
393 /* ------------------------------------------------------------ */ | |
394 /** Remove a request attribute. | |
395 * This method is a convenience method to call the {@link ServletRequest#removeAttribute(String)} | |
396 * method on the associated request object. | |
397 * This is a thread safe call and may be called by any thread. | |
398 * @param name the attribute name | |
399 */ | |
400 public void removeAttribute(String name); | |
401 | |
402 /* ------------------------------------------------------------ */ | |
403 /** | |
404 * Undispatch the request. | |
405 * <p> | |
406 * This method can be called on a suspended continuation in order | |
407 * to exit the dispatch to the filter/servlet by throwing a {@link ContinuationThrowable} | |
408 * which is caught either by the container or the {@link ContinuationFilter}. | |
409 * This is an alternative to simply returning from the dispatch in the case | |
410 * where filters in the filter chain may not be prepared to handle a suspended | |
411 * request. | |
412 * </p> | |
413 * This method should only be used as a last resort and a normal return is a prefereable | |
414 * solution if filters can be updated to handle that case. | |
415 * | |
416 * @throws ContinuationThrowable thrown if the request is suspended. The instance of the | |
417 * exception may be reused on subsequent calls, so the stack frame may not be accurate. | |
418 */ | |
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419 // public void undispatch() throws ContinuationThrowable; |
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420 } |