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/*
* Copyright 2006-2007 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.batch.retry.support;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.batch.repeat.RepeatException;
import org.springframework.batch.retry.ExhaustedRetryException;
import org.springframework.batch.retry.RecoveryCallback;
import org.springframework.batch.retry.RetryCallback;
import org.springframework.batch.retry.RetryContext;
import org.springframework.batch.retry.RetryException;
import org.springframework.batch.retry.RetryListener;
import org.springframework.batch.retry.RetryOperations;
import org.springframework.batch.retry.RetryPolicy;
import org.springframework.batch.retry.RetryState;
import org.springframework.batch.retry.TerminatedRetryException;
import org.springframework.batch.retry.backoff.BackOffContext;
import org.springframework.batch.retry.backoff.BackOffInterruptedException;
import org.springframework.batch.retry.backoff.BackOffPolicy;
import org.springframework.batch.retry.backoff.NoBackOffPolicy;
import org.springframework.batch.retry.policy.MapRetryContextCache;
import org.springframework.batch.retry.policy.RetryContextCache;
import org.springframework.batch.retry.policy.SimpleRetryPolicy;
/**
* Template class that simplifies the execution of operations with retry
* semantics.
* Retryable operations are encapsulated in implementations of the
* {@link RetryCallback} interface and are executed using one of the supplied
* execute methods.
*
* By default, an operation is retried if is throws any {@link Exception} or
* subclass of {@link Exception}. This behaviour can be changed by using the
* {@link #setRetryPolicy(RetryPolicy)} method.
*
* Also by default, each operation is retried for a maximum of three attempts
* with no back off in between. This behaviour can be configured using the
* {@link #setRetryPolicy(RetryPolicy)} and
* {@link #setBackOffPolicy(BackOffPolicy)} properties. The
* {@link org.springframework.batch.retry.backoff.BackOffPolicy} controls how
* long the pause is between each individual retry attempt.
*
* This class is thread-safe and suitable for concurrent access when executing
* operations and when performing configuration changes. As such, it is possible
* to change the number of retries on the fly, as well as the
* {@link BackOffPolicy} used and no in progress retryable operations will be
* affected.
*
* @author Rob Harrop
* @author Dave Syer
*/
public class RetryTemplate implements RetryOperations {
protected final Log logger = LogFactory.getLog(getClass());
private volatile BackOffPolicy backOffPolicy = new NoBackOffPolicy();
private volatile RetryPolicy retryPolicy = new SimpleRetryPolicy(3, Collections
., Boolean> singletonMap(Exception.class, true));
private volatile RetryListener[] listeners = new RetryListener[0];
private RetryContextCache retryContextCache = new MapRetryContextCache();
/**
* Public setter for the {@link RetryContextCache}.
*
* @param retryContextCache the {@link RetryContextCache} to set.
*/
public void setRetryContextCache(RetryContextCache retryContextCache) {
this.retryContextCache = retryContextCache;
}
/**
* Setter for listeners. The listeners are executed before and after a retry
* block (i.e. before and after all the attempts), and on an error (every
* attempt).
*
* @param listeners
* @see RetryListener
*/
public void setListeners(RetryListener[] listeners) {
this.listeners = Arrays.asList(listeners).toArray(new RetryListener[listeners.length]);
}
/**
* Register an additional listener.
*
* @param listener
* @see #setListeners(RetryListener[])
*/
public void registerListener(RetryListener listener) {
List list = new ArrayList(Arrays.asList(listeners));
list.add(listener);
listeners = list.toArray(new RetryListener[list.size()]);
}
/**
* Setter for {@link BackOffPolicy}.
*
* @param backOffPolicy
*/
public void setBackOffPolicy(BackOffPolicy backOffPolicy) {
this.backOffPolicy = backOffPolicy;
}
/**
* Setter for {@link RetryPolicy}.
*
* @param retryPolicy
*/
public void setRetryPolicy(RetryPolicy retryPolicy) {
this.retryPolicy = retryPolicy;
}
/**
* Keep executing the callback until it either succeeds or the policy
* dictates that we stop, in which case the most recent exception thrown by
* the callback will be rethrown.
*
* @see RetryOperations#execute(RetryCallback)
*
* @throws TerminatedRetryException if the retry has been manually
* terminated by a listener.
*/
public final T execute(RetryCallback retryCallback) throws Exception {
return doExecute(retryCallback, null, null);
}
/**
* Keep executing the callback until it either succeeds or the policy
* dictates that we stop, in which case the recovery callback will be
* executed.
*
* @see RetryOperations#execute(RetryCallback, RecoveryCallback)
*
* @throws TerminatedRetryException if the retry has been manually
* terminated by a listener.
*/
public final T execute(RetryCallback retryCallback, RecoveryCallback recoveryCallback) throws Exception {
return doExecute(retryCallback, recoveryCallback, null);
}
/**
* Execute the callback once if the policy dictates that we can, re-throwing
* any exception encountered so that clients can re-present the same task
* later.
*
* @see RetryOperations#execute(RetryCallback, RetryState)
*
* @throws ExhaustedRetryException if the retry has been exhausted.
*/
public final T execute(RetryCallback retryCallback, RetryState retryState) throws Exception,
ExhaustedRetryException {
return doExecute(retryCallback, null, retryState);
}
/**
* Execute the callback once if the policy dictates that we can, re-throwing
* any exception encountered so that clients can re-present the same task
* later.
*
* @see RetryOperations#execute(RetryCallback, RetryState)
*/
public final T execute(RetryCallback retryCallback, RecoveryCallback recoveryCallback,
RetryState retryState) throws Exception, ExhaustedRetryException {
return doExecute(retryCallback, recoveryCallback, retryState);
}
/**
* Execute the callback once if the policy dictates that we can, otherwise
* execute the recovery callback.
*
* @see RetryOperations#execute(RetryCallback, RecoveryCallback, RetryState)
* @throws ExhaustedRetryException if the retry has been exhausted.
*/
protected T doExecute(RetryCallback retryCallback, RecoveryCallback recoveryCallback, RetryState state)
throws Exception, ExhaustedRetryException {
RetryPolicy retryPolicy = this.retryPolicy;
BackOffPolicy backOffPolicy = this.backOffPolicy;
// Allow the retry policy to initialise itself...
RetryContext context = open(retryPolicy, state);
logger.debug("RetryContext retrieved: " + context);
// Make sure the context is available globally for clients who need
// it...
RetrySynchronizationManager.register(context);
Throwable lastException = null;
try {
// Give clients a chance to enhance the context...
boolean running = doOpenInterceptors(retryCallback, context);
if (!running) {
throw new TerminatedRetryException("Retry terminated abnormally by interceptor before first attempt");
}
// Start the backoff context...
BackOffContext backOffContext = backOffPolicy.start(context);
/*
* We allow the whole loop to be skipped if the policy or context
* already forbid the first try. This is used in the case of
* external retry to allow a recovery in handleRetryExhausted
* without the callback processing (which would throw an exception).
*/
while (canRetry(retryPolicy, context) && !context.isExhaustedOnly()) {
try {
logger.debug("Retry: count=" + context.getRetryCount());
// Reset the last exception, so if we are successful
// the close interceptors will not think we failed...
lastException = null;
return retryCallback.doWithRetry(context);
}
catch (Throwable e) {
lastException = e;
doOnErrorInterceptors(retryCallback, context, e);
registerThrowable(retryPolicy, state, context, e);
if (canRetry(retryPolicy, context) && !context.isExhaustedOnly()) {
try {
backOffPolicy.backOff(backOffContext);
}
catch (BackOffInterruptedException ex) {
lastException = e;
// back off was prevented by another thread - fail
// the retry
logger.debug("Abort retry because interrupted: count=" + context.getRetryCount());
throw ex;
}
}
logger.debug("Checking for rethrow: count=" + context.getRetryCount());
if (shouldRethrow(retryPolicy, context, state)) {
logger.debug("Rethrow in retry for policy: count=" + context.getRetryCount());
throw wrapIfNecessary(e);
}
}
/*
* A stateful attempt that can retry should have rethrown the
* exception by now - i.e. we shouldn't get this far for a
* stateful attempt if it can retry.
*/
}
logger.debug("Retry failed last attempt: count=" + context.getRetryCount());
if (context.isExhaustedOnly()) {
throw new ExhaustedRetryException("Retry exhausted after last attempt with no recovery path.", context
.getLastThrowable());
}
return handleRetryExhausted(recoveryCallback, context, state);
}
finally {
close(retryPolicy, context, state, lastException == null);
doCloseInterceptors(retryCallback, context, lastException);
RetrySynchronizationManager.clear();
}
}
/**
* Decide whether to proceed with the ongoing retry attempt. This method is
* called before the {@link RetryCallback} is executed, but after the
* backoff and open interceptors.
*
* @param retryPolicy the policy to apply
* @param context the current retry context
* @return true if we can continue with the attempt
*/
protected boolean canRetry(RetryPolicy retryPolicy, RetryContext context) {
return retryPolicy.canRetry(context);
}
/**
* Clean up the cache if necessary and close the context provided (if the
* flag indicates that processing was successful).
*
* @param context
* @param state
* @param succeeded
*/
protected void close(RetryPolicy retryPolicy, RetryContext context, RetryState state, boolean succeeded) {
if (state != null) {
if (succeeded) {
retryContextCache.remove(state.getKey());
retryPolicy.close(context);
}
}
else {
retryPolicy.close(context);
}
}
/**
* @param retryPolicy
* @param state
* @param context
* @param e
*/
protected void registerThrowable(RetryPolicy retryPolicy, RetryState state, RetryContext context, Throwable e) {
if (state != null) {
Object key = state.getKey();
if (context.getRetryCount() > 0 && !retryContextCache.containsKey(key)) {
throw new RetryException("Inconsistent state for failed item key: cache key has changed. "
+ "Consider whether equals() or hashCode() for the key might be inconsistent, "
+ "or if you need to supply a better key");
}
retryContextCache.put(key, context);
}
retryPolicy.registerThrowable(context, e);
}
/**
* Delegate to the {@link RetryPolicy} having checked in the cache for an
* existing value if the state is not null.
*
* @param retryPolicy a {@link RetryPolicy} to delegate the context creation
* @return a retry context, either a new one or the one used last time the
* same state was encountered
*/
protected RetryContext open(RetryPolicy retryPolicy, RetryState state) {
if (state == null) {
return doOpenInternal(retryPolicy);
}
Object key = state.getKey();
if (state.isForceRefresh()) {
return doOpenInternal(retryPolicy);
}
// If there is no cache hit we can avoid the possible expense of the
// cache re-hydration.
if (!retryContextCache.containsKey(key)) {
// The cache is only used if there is a failure.
return doOpenInternal(retryPolicy);
}
RetryContext context = retryContextCache.get(key);
if (context == null) {
if (retryContextCache.containsKey(key)) {
throw new RetryException("Inconsistent state for failed item: no history found. "
+ "Consider whether equals() or hashCode() for the item might be inconsistent, "
+ "or if you need to supply a better ItemKeyGenerator");
}
// The cache could have been expired in between calls to
// containsKey(), so we have to live with this:
return doOpenInternal(retryPolicy);
}
return context;
}
/**
* @param retryPolicy
* @return
*/
private RetryContext doOpenInternal(RetryPolicy retryPolicy) {
return retryPolicy.open(RetrySynchronizationManager.getContext());
}
/**
* Actions to take after final attempt has failed. If there is state clean
* up the cache. If there is a recovery callback, execute that and return
* its result. Otherwise throw an exception.
*
* @param recoveryCallback the callback for recovery (might be null)
* @param context the current retry context
* @throws Exception if the callback does, and if there is no callback and
* the state is null then the last exception from the context
* @throws ExhaustedRetryException if the state is not null and there is no
* recovery callback
*/
protected T handleRetryExhausted(RecoveryCallback recoveryCallback, RetryContext context, RetryState state)
throws Exception {
if (state != null) {
retryContextCache.remove(state.getKey());
}
if (recoveryCallback != null) {
return recoveryCallback.recover(context);
}
if (state != null) {
logger.debug("Retry exhausted after last attempt with no recovery path.");
throw new ExhaustedRetryException("Retry exhausted after last attempt with no recovery path", context
.getLastThrowable());
}
throw wrapIfNecessary(context.getLastThrowable());
}
/**
* Extension point for subclasses to decide on behaviour after catching an
* exception in a {@link RetryCallback}. Normal stateless behaviour is not
* to rethrow, and if there is state we rethrow.
*
* @param retryPolicy
* @param context the current context
*
* @return true if the state is not null but subclasses might choose
* otherwise
*/
protected boolean shouldRethrow(RetryPolicy retryPolicy, RetryContext context, RetryState state) {
if (state == null) {
return false;
}
else {
return state.rollbackFor(context.getLastThrowable());
}
}
private boolean doOpenInterceptors(RetryCallback callback, RetryContext context) {
boolean result = true;
for (int i = 0; i < listeners.length; i++) {
result = result && listeners[i].open(context, callback);
}
return result;
}
private void doCloseInterceptors(RetryCallback callback, RetryContext context, Throwable lastException) {
for (int i = listeners.length; i-- > 0;) {
listeners[i].close(context, callback, lastException);
}
}
private void doOnErrorInterceptors(RetryCallback callback, RetryContext context, Throwable throwable) {
for (int i = listeners.length; i-- > 0;) {
listeners[i].onError(context, callback, throwable);
}
}
/**
* Re-throws the original throwable if it is unchecked, wraps checked
* exceptions into {@link RepeatException}.
*/
private static Exception wrapIfNecessary(Throwable throwable) {
if (throwable instanceof Error) {
throw (Error) throwable;
}
else if (throwable instanceof Exception) {
return (Exception) throwable;
}
else {
return new RetryException("Exception in batch process", throwable);
}
}
}
