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/*
 * Copyright (c) 2010-2015 Pivotal Software, Inc. All rights reserved.
 *
 * 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. See accompanying
 * LICENSE file.
 */

package com.gemstone.gemfire.cache;

/** A user-defined object defined in the {@link RegionAttributes} that is
 * called synchronously before a region or entry in the cache is
 * modified. The typical use for a CacheWriter is to update a database.
 * Application writers should implement these methods to execute
 * application-specific behavior before the cache is modified.
 *
 * 

Before the region is updated via a put, create, or destroy operation, * GemFire will call a CacheWriter that is installed anywhere in any * participating cache for that region, preferring a local CacheWriter * if there is one. Usually there will be only one CacheWriter in * the distributed system. If there are multiple CacheWriters * available in the distributed system, the GemFire * implementation always prefers one that is stored locally, or else picks one * arbitrarily; in any case only one CacheWriter will be invoked. * *

The CacheWriter is capable of aborting the update to the cache by throwing * a CacheWriterException. This exception or any runtime exception * thrown by the CacheWriter will abort the operation and the * exception will be propagated to the initiator of the operation, regardless * of whether the initiator is in the same VM as the CacheWriter. * * @author Eric Zoerner * * @see AttributesFactory#setCacheWriter * @see RegionAttributes#getCacheWriter * @see AttributesMutator#setCacheWriter * @since 3.0 */ public interface CacheWriter extends CacheCallback { /** * Called before an entry is updated. The entry update is initiated by a put * or a get that causes the loader to update an existing entry. * The entry previously existed in the cache where the operation was * initiated, although the old value may have been null. The entry being * updated may or may not exist in the local cache where the CacheWriter is * installed. * * @param event an EntryEvent that provides information about the operation in progress * @throws CacheWriterException if thrown will abort the operation in progress, * and the exception will be propagated back to caller that initiated * the operation * @see Region#put(Object, Object) * @see Region#get(Object) */ public void beforeUpdate(EntryEvent event) throws CacheWriterException; /** Called before an entry is created. Entry creation is initiated by a * create, a put, or a get. * The CacheWriter can determine whether this value comes from a * get or not by evaluating the {@link CacheEvent#getOperation() Operation}'s {@link Operation#isLoad()} method. * The entry being created may already exist in the local cache where this CacheWriter * is installed, but it does not yet exist in the cache where the operation was initiated. * @param event an EntryEvent that provides information about the operation in progress * @throws CacheWriterException if thrown will abort the operation in progress, * and the exception will be propagated back to caller that initiated * the operation * @see Region#create(Object, Object) * @see Region#put(Object, Object) * @see Region#get(Object) */ public void beforeCreate(EntryEvent event) throws CacheWriterException; /** * Called before an entry is destroyed. The entry being destroyed may or may * not exist in the local cache where the CacheWriter is installed. This method * is not called as a result of expiration or * {@link Region#localDestroy(Object)}. * * @param event an EntryEvent that provides information about the operation in progress * @throws CacheWriterException if thrown will abort the operation in progress, * and the exception will be propagated back to caller that initiated * the operation * * @see Region#destroy(Object) */ public void beforeDestroy(EntryEvent event) throws CacheWriterException; /** * Called before a region is destroyed. The CacheWriter * will not additionally be called for each entry that is destroyed * in the region as a result of a region destroy. If the region's * subregions have CacheWriters installed, then they * will be called for the cascading subregion destroys. * This method is not called as a result of * expiration or {@link Region#localDestroyRegion()}. However, the * {@link Region#close} method is invoked regardless of whether a * region is destroyed locally. A non-local region destroy results * in an invocation of {@link #beforeRegionDestroy} followed by an * invocation of {@link Region#close}. *

* WARNING: This method should not destroy or create any regions itself or a * deadlock will occur. * * @param event * a RegionEvent that provides information about the operation * * @throws CacheWriterException * if thrown, will abort the operation in progress, and the * exception will be propagated back to the caller that * initiated the operation * * @see Region#destroyRegion() */ public void beforeRegionDestroy(RegionEvent event) throws CacheWriterException; /** * Called before a region is cleared. The CacheWriter * will not additionally be called for each entry that is cleared * in the region as a result of a region clear. * *

* WARNING: This method should not clear/destroy any regions * * * @param event * a RegionEvent that provides information about the operation * * @throws CacheWriterException * if thrown, will abort the operation in progress, and the * exception will be propagated back to the caller that * initiated the operation * * @see Region#clear */ public void beforeRegionClear(RegionEvent event) throws CacheWriterException; }





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