1 | /* |
2 | * Copyright 2006-2007 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.batch.retry.support; |
18 | |
19 | import java.util.ArrayList; |
20 | import java.util.Arrays; |
21 | import java.util.List; |
22 | |
23 | import org.apache.commons.logging.Log; |
24 | import org.apache.commons.logging.LogFactory; |
25 | import org.springframework.batch.retry.RetryCallback; |
26 | import org.springframework.batch.retry.RetryContext; |
27 | import org.springframework.batch.retry.RetryException; |
28 | import org.springframework.batch.retry.RetryListener; |
29 | import org.springframework.batch.retry.RetryOperations; |
30 | import org.springframework.batch.retry.RetryPolicy; |
31 | import org.springframework.batch.retry.TerminatedRetryException; |
32 | import org.springframework.batch.retry.backoff.BackOffContext; |
33 | import org.springframework.batch.retry.backoff.BackOffInterruptedException; |
34 | import org.springframework.batch.retry.backoff.BackOffPolicy; |
35 | import org.springframework.batch.retry.backoff.NoBackOffPolicy; |
36 | import org.springframework.batch.retry.policy.SimpleRetryPolicy; |
37 | |
38 | /** |
39 | * Template class that simplifies the execution of operations with retry |
40 | * semantics. <br/> Retryable operations are encapsulated in implementations of |
41 | * the {@link RetryCallback} interface and are executed using one of the |
42 | * supplied {@link #execute} methods. <br/> |
43 | * |
44 | * By default, an operation is retried if is throws any {@link Exception} or |
45 | * subclass of {@link Exception}. This behaviour can be changed by using the |
46 | * {@link #setRetryPolicy(RetryPolicy)} method. <br/> |
47 | * |
48 | * Also by default, each operation is retried for a maximum of three attempts |
49 | * with no back off in between. This behaviour can be configured using the |
50 | * {@link #setRetryPolicy(RetryPolicy)} and |
51 | * {@link #setBackOffPolicy(BackOffPolicy)} properties. The |
52 | * {@link org.springframework.batch.retry.backoff.BackOffPolicy} controls how |
53 | * long the pause is between each individual retry attempt. <br/> |
54 | * |
55 | * This class is thread-safe and suitable for concurrent access when executing |
56 | * operations and when performing configuration changes. As such, it is possible |
57 | * to change the number of retries on the fly, as well as the |
58 | * {@link BackOffPolicy} used and no in progress retryable operations will be |
59 | * affected. |
60 | * |
61 | * @author Rob Harrop |
62 | * @author Dave Syer |
63 | */ |
64 | public class RetryTemplate implements RetryOperations { |
65 | |
66 | protected final Log logger = LogFactory.getLog(getClass()); |
67 | |
68 | private volatile BackOffPolicy backOffPolicy = new NoBackOffPolicy(); |
69 | |
70 | private volatile RetryPolicy retryPolicy = new SimpleRetryPolicy(); |
71 | |
72 | private volatile RetryListener[] listeners = new RetryListener[0]; |
73 | |
74 | /** |
75 | * Setter for listeners. The listeners are executed before and after a retry |
76 | * block (i.e. before and after all the attempts), and on an error (every |
77 | * attempt). |
78 | * @param listeners |
79 | * @see RetryListener |
80 | */ |
81 | public void setListeners(RetryListener[] listeners) { |
82 | this.listeners = listeners; |
83 | } |
84 | |
85 | /** |
86 | * Register an additional listener. |
87 | * @param listener |
88 | * @see #setListeners(RetryListener[]) |
89 | */ |
90 | public void registerListener(RetryListener listener) { |
91 | List list = new ArrayList(Arrays.asList(listeners)); |
92 | list.add(listener); |
93 | listeners = (RetryListener[]) list.toArray(new RetryListener[list.size()]); |
94 | } |
95 | |
96 | /** |
97 | * Setter for {@link BackOffPolicy}. |
98 | * @param backOffPolicy |
99 | */ |
100 | public void setBackOffPolicy(BackOffPolicy backOffPolicy) { |
101 | this.backOffPolicy = backOffPolicy; |
102 | } |
103 | |
104 | /** |
105 | * Setter for {@link RetryPolicy}. |
106 | * |
107 | * @param retryPolicy |
108 | */ |
109 | public void setRetryPolicy(RetryPolicy retryPolicy) { |
110 | this.retryPolicy = retryPolicy; |
111 | } |
112 | |
113 | /** |
114 | * Keep executing the callback until it either succeeds or the policy |
115 | * dictates that we stop, in which case the most recent exception thrown by |
116 | * the callback will be rethrown. |
117 | * |
118 | * @see org.springframework.batch.retry.RetryOperations#execute(org.springframework.batch.retry.RetryCallback) |
119 | * |
120 | * @throws TerminatedRetryException if the retry has been manually |
121 | * terminated through the {@link RetryContext}. |
122 | */ |
123 | public final Object execute(RetryCallback callback) throws Exception { |
124 | |
125 | /* |
126 | * Read all needed data into local variables to prevent any |
127 | * reference/primitive changes on other threads affecting this retry |
128 | * attempt. |
129 | */ |
130 | BackOffPolicy backOffPolicy = this.backOffPolicy; |
131 | RetryPolicy retryPolicy = this.retryPolicy; |
132 | |
133 | // Allow the retry policy to initialise itself... |
134 | // TODO: catch and rethrow abnormal retry exception? |
135 | RetryContext context = retryPolicy.open(callback, RetrySynchronizationManager.getContext()); |
136 | |
137 | // Make sure the context is available globally for clients who need |
138 | // it... |
139 | RetrySynchronizationManager.register(context); |
140 | |
141 | Throwable lastException = null; |
142 | |
143 | try { |
144 | |
145 | // Give clients a chance to enhance the context... |
146 | boolean running = doOpenInterceptors(callback, context); |
147 | |
148 | if (!running) { |
149 | throw new TerminatedRetryException("Retry terminated abnormally by interceptor before first attempt"); |
150 | } |
151 | |
152 | // Start the backoff context... |
153 | BackOffContext backOffContext = backOffPolicy.start(context); |
154 | |
155 | /* |
156 | * We allow the whole loop to be skipped if the policy or context |
157 | * already forbid the first try. This is used in the case of |
158 | * external retry to allow a recovery in handleRetryExhausted |
159 | * without the callback processing (which would throw an exception). |
160 | */ |
161 | while (retryPolicy.canRetry(context) && !context.isExhaustedOnly()) { |
162 | |
163 | try { |
164 | logger.debug("Retry: count=" + context.getRetryCount()); |
165 | // Reset the last exception, so if we are successful |
166 | // the close interceptors will not think we failed... |
167 | lastException = null; |
168 | return callback.doWithRetry(context); |
169 | } |
170 | catch (Throwable ex) { |
171 | Throwable throwable = unwrapIfRethrown(ex); |
172 | lastException = throwable; |
173 | |
174 | doOnErrorInterceptors(callback, context, throwable); |
175 | |
176 | retryPolicy.registerThrowable(context, throwable); |
177 | |
178 | if (retryPolicy.shouldRethrow(context)) { |
179 | logger.debug("Rethrow in retry for policy: count=" + context.getRetryCount()); |
180 | rethrow(throwable); |
181 | } |
182 | |
183 | } |
184 | |
185 | try { |
186 | backOffPolicy.backOff(backOffContext); |
187 | } |
188 | catch (BackOffInterruptedException e) { |
189 | lastException = e; |
190 | // back off was prevented by another thread - fail the |
191 | // retry |
192 | logger.debug("Abort retry because interrupted: count=" + context.getRetryCount()); |
193 | rethrow(e); |
194 | } |
195 | |
196 | /* |
197 | * A stateful policy that can retry should have rethrown the |
198 | * exception by now - i.e. we shouldn't get this far for a |
199 | * stateful policy if it can retry. |
200 | */ |
201 | } |
202 | |
203 | logger.debug("Retry failed last attempt: count=" + context.getRetryCount()); |
204 | return retryPolicy.handleRetryExhausted(context); |
205 | |
206 | } |
207 | finally { |
208 | retryPolicy.close(context); |
209 | doCloseInterceptors(callback, context, lastException); |
210 | RetrySynchronizationManager.clear(); |
211 | } |
212 | } |
213 | |
214 | private boolean doOpenInterceptors(RetryCallback callback, RetryContext context) { |
215 | |
216 | boolean result = true; |
217 | |
218 | for (int i = 0; i < listeners.length; i++) { |
219 | result = result && listeners[i].open(context, callback); |
220 | } |
221 | |
222 | return result; |
223 | |
224 | } |
225 | |
226 | private void doCloseInterceptors(RetryCallback callback, RetryContext context, Throwable lastException) { |
227 | for (int i = listeners.length; i-- > 0;) { |
228 | listeners[i].close(context, callback, lastException); |
229 | } |
230 | } |
231 | |
232 | private void doOnErrorInterceptors(RetryCallback callback, RetryContext context, Throwable throwable) { |
233 | for (int i = listeners.length; i-- > 0;) { |
234 | listeners[i].onError(context, callback, throwable); |
235 | } |
236 | } |
237 | |
238 | /** |
239 | * Re-throw the exception directly if possible, wrap custom Throwables into |
240 | * {@link UnclassifiedRetryException}. |
241 | */ |
242 | private static void rethrow(Throwable throwable) throws Exception { |
243 | if (throwable instanceof Exception) { |
244 | throw (Exception) throwable; |
245 | } |
246 | else if (throwable instanceof Error) { |
247 | throw (Error) throwable; |
248 | } |
249 | else { |
250 | throw new UnclassifiedRetryException("Unclassified Throwable encountered", throwable); |
251 | } |
252 | } |
253 | |
254 | /** |
255 | * Undo the wrapping done in {@link #rethrow(Throwable)} |
256 | */ |
257 | private static Throwable unwrapIfRethrown(Throwable throwable) { |
258 | if (throwable instanceof UnclassifiedRetryException) { |
259 | return throwable.getCause(); |
260 | } |
261 | else { |
262 | return throwable; |
263 | } |
264 | } |
265 | |
266 | /** |
267 | * Runtime exception wrapper for Throwables that are neither Exception nor |
268 | * Error. |
269 | */ |
270 | private static class UnclassifiedRetryException extends RetryException { |
271 | |
272 | public UnclassifiedRetryException(String msg, Throwable cause) { |
273 | super(msg, cause); |
274 | } |
275 | |
276 | } |
277 | |
278 | } |