Package org.apache.geode.cache

Interface CacheWriter<K,V>

All Superinterfaces:
CacheCallback, Declarable
All Known Implementing Classes:
CacheWriterAdapter
public interface CacheWriter<K,V> extends CacheCallback
A user-defined object defined in the 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.

WARNING: To avoid risk of deadlock, do not invoke CacheFactory.getAnyInstance() from within any callback methods. Instead use EntryEvent.getRegion().getCache() or RegionEvent.getRegion().getCache().

Since:
GemFire 3.0
See Also:

  • Method Details

    • beforeUpdate

      void beforeUpdate(EntryEvent<K,V> event) throws CacheWriterException
      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.
      Parameters:
      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 Also:

    • beforeCreate

      void beforeCreate(EntryEvent<K,V> 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 Operation's 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.
      Parameters:
      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 Also:

    • beforeDestroy

      void beforeDestroy(EntryEvent<K,V> 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 Region.localDestroy(Object).
      Parameters:
      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 Also:

    • beforeRegionDestroy

      void beforeRegionDestroy(RegionEvent<K,V> 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 Region.close(), Cache.close(boolean), or Region.localDestroyRegion(). However, the Region.close() method is invoked regardless of whether a region is destroyed locally. A non-local region destroy results in an invocation of this method is followed by an invocation of Region.close().

      WARNING: This method should not destroy or create any regions itself or a deadlock will occur.

      Parameters:
      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 Also:

    • beforeRegionClear

      void beforeRegionClear(RegionEvent<K,V> 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

      Parameters:
      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 Also: