| // Copyright (C) 2009 The Android Open Source Project |
| // |
| // 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 com.google.gerrit.server.cache; |
| |
| /** |
| * Creates a cache entry on demand when its not found. |
| * |
| * @param <K> type of the cache's key. |
| * @param <V> type of the cache's value element. |
| */ |
| public abstract class EntryCreator<K, V> { |
| /** |
| * Invoked on a cache miss, to compute the cache entry. |
| * |
| * @param key entry whose content needs to be obtained. |
| * @return new cache content. The caller will automatically put this object |
| * into the cache. |
| * @throws Exception the cache content cannot be computed. No entry will be |
| * stored in the cache, and {@link #missing(Object)} will be invoked |
| * instead. Future requests for the same key will retry this method. |
| */ |
| public abstract V createEntry(K key) throws Exception; |
| |
| /** Invoked when {@link #createEntry(Object)} fails, by default return null. */ |
| public V missing(K key) { |
| return null; |
| } |
| } |