| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more contributor license |
| * agreements. See the NOTICE file distributed with this work for additional information regarding |
| * copyright ownership. The ASF licenses this file to You 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.apache.geode.cache; |
| |
| /** |
| * Allows data from outside of the VM to be placed into a region. When |
| * {@link org.apache.geode.cache.Region#get(Object)} is called for a region entry that has a |
| * <code>null</code> value, the {@link CacheLoader#load load} method of the region's cache loader is |
| * invoked. The <code>load</code> method creates the value for the desired key by performing an |
| * operation such as a database query. The <code>load</code> may also perform a |
| * {@linkplain LoaderHelper#netSearch net search} that will look for the value in a cache instance |
| * hosted by another member of the distributed system. |
| * <p> |
| * WARNING: To avoid risk of deadlock, do not invoke CacheFactory.getAnyInstance() from within any |
| * callback methods. Instead use LoaderHelper.getRegion().getCache(). |
| * <p> |
| * |
| * @see AttributesFactory#setCacheLoader |
| * @see RegionAttributes#getCacheLoader |
| * @see AttributesMutator#setCacheLoader |
| * @since GemFire 2.0 |
| */ |
| public interface CacheLoader<K, V> extends CacheCallback { |
| /** |
| * Loads a value. Application writers should implement this method to customize the loading of a |
| * value. This method is called by the caching service when the requested value is not in the |
| * cache. Any exception (including an unchecked exception) thrown by this method is propagated |
| * back to and thrown by the invocation of {@link Region#get(Object, Object)} that triggered this |
| * load. |
| * <p> |
| * |
| * @param helper a LoaderHelper object that is passed in from cache service and provides access to |
| * the key, region, argument, and <code>netSearch</code>. |
| * @return the value supplied for this key, or null if no value can be supplied. A local loader |
| * will always be invoked if one exists. Otherwise one remote loader is invoked. Returning |
| * <code>null</code> causes {@link Region#get(Object, Object)} to return |
| * <code>null</code>. |
| * @throws CacheLoaderException if an error occurs. This exception or any other exception thrown |
| * by this method will be propagated back to the application from the get method. |
| * |
| * @see Region#get(Object, Object) Region.get |
| */ |
| V load(LoaderHelper<K, V> helper) throws CacheLoaderException; |
| } |