| /* |
| * Copyright (C) 2011 The Guava 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 com.google.common.cache; |
| |
| import static com.google.common.base.Preconditions.checkNotNull; |
| |
| import com.google.common.annotations.Beta; |
| import com.google.common.annotations.GwtCompatible; |
| import com.google.common.base.Function; |
| import com.google.common.base.Supplier; |
| |
| import java.io.Serializable; |
| import java.util.Map; |
| |
| /** |
| * Computes or retrieves values, based on a key, for use in populating a {@link LoadingCache}. |
| * |
| * <p>Most implementations will only need to implement {@link #load}. Other methods may be |
| * overridden as desired. |
| * |
| * <p>Usage example: <pre> {@code |
| * |
| * CacheLoader<Key, Graph> loader = new CacheLoader<Key, Graph>() { |
| * public Graph load(Key key) throws AnyException { |
| * return createExpensiveGraph(key); |
| * } |
| * }; |
| * LoadingCache<Key, Graph> cache = CacheBuilder.newBuilder().build(loader);}</pre> |
| * |
| * @author Charles Fry |
| * @since 10.0 |
| */ |
| @GwtCompatible(emulated = true) |
| public abstract class CacheLoader<K, V> { |
| /** |
| * Constructor for use by subclasses. |
| */ |
| protected CacheLoader() {} |
| |
| /** |
| * Computes or retrieves the value corresponding to {@code key}. |
| * |
| * @param key the non-null key whose value should be loaded |
| * @return the value associated with {@code key}; <b>must not be null</b> |
| * @throws Exception if unable to load the result |
| * @throws InterruptedException if this method is interrupted. {@code InterruptedException} is |
| * treated like any other {@code Exception} in all respects except that, when it is caught, |
| * the thread's interrupt status is set |
| */ |
| public abstract V load(K key) throws Exception; |
| |
| /** |
| * Computes or retrieves the values corresponding to {@code keys}. This method is called by |
| * {@link LoadingCache#getAll}. |
| * |
| * <p>If the returned map doesn't contain all requested {@code keys} then the entries it does |
| * contain will be cached, but {@code getAll} will throw an exception. If the returned map |
| * contains extra keys not present in {@code keys} then all returned entries will be cached, |
| * but only the entries for {@code keys} will be returned from {@code getAll}. |
| * |
| * <p>This method should be overriden when bulk retrieval is significantly more efficient than |
| * many individual lookups. Note that {@link LoadingCache#getAll} will defer to individual calls |
| * to {@link LoadingCache#get} if this method is not overriden. |
| * |
| * @param keys the unique, non-null keys whose values should be loaded |
| * @return a map from each key in {@code keys} to the value associated with that key; |
| * <b>may not contain null values</b> |
| * @throws Exception if unable to load the result |
| * @throws InterruptedException if this method is interrupted. {@code InterruptedException} is |
| * treated like any other {@code Exception} in all respects except that, when it is caught, |
| * the thread's interrupt status is set |
| * @since 11.0 |
| */ |
| public Map<K, V> loadAll(Iterable<? extends K> keys) throws Exception { |
| // This will be caught by getAll(), causing it to fall back to multiple calls to |
| // LoadingCache.get |
| throw new UnsupportedLoadingOperationException(); |
| } |
| |
| /** |
| * Returns a cache loader based on an <i>existing</i> function instance. Note that there's no need |
| * to create a <i>new</i> function just to pass it in here; just subclass {@code CacheLoader} and |
| * implement {@link #load load} instead. |
| * |
| * @param function the function to be used for loading values; must never return {@code null} |
| * @return a cache loader that loads values by passing each key to {@code function} |
| */ |
| @Beta |
| public static <K, V> CacheLoader<K, V> from(Function<K, V> function) { |
| return new FunctionToCacheLoader<K, V>(function); |
| } |
| |
| private static final class FunctionToCacheLoader<K, V> |
| extends CacheLoader<K, V> implements Serializable { |
| private final Function<K, V> computingFunction; |
| |
| public FunctionToCacheLoader(Function<K, V> computingFunction) { |
| this.computingFunction = checkNotNull(computingFunction); |
| } |
| |
| @Override |
| public V load(K key) { |
| return computingFunction.apply(checkNotNull(key)); |
| } |
| |
| private static final long serialVersionUID = 0; |
| } |
| |
| /** |
| * Returns a cache loader based on an <i>existing</i> supplier instance. Note that there's no need |
| * to create a <i>new</i> supplier just to pass it in here; just subclass {@code CacheLoader} and |
| * implement {@link #load load} instead. |
| * |
| * @param supplier the supplier to be used for loading values; must never return {@code null} |
| * @return a cache loader that loads values by calling {@link Supplier#get}, irrespective of the |
| * key |
| */ |
| @Beta |
| public static <V> CacheLoader<Object, V> from(Supplier<V> supplier) { |
| return new SupplierToCacheLoader<V>(supplier); |
| } |
| |
| private static final class SupplierToCacheLoader<V> |
| extends CacheLoader<Object, V> implements Serializable { |
| private final Supplier<V> computingSupplier; |
| |
| public SupplierToCacheLoader(Supplier<V> computingSupplier) { |
| this.computingSupplier = checkNotNull(computingSupplier); |
| } |
| |
| @Override |
| public V load(Object key) { |
| checkNotNull(key); |
| return computingSupplier.get(); |
| } |
| |
| private static final long serialVersionUID = 0; |
| } |
| |
| static final class UnsupportedLoadingOperationException extends UnsupportedOperationException {} |
| |
| /** |
| * Thrown to indicate that an invalid response was returned from a call to {@link CacheLoader}. |
| * |
| * @since 11.0 |
| */ |
| public static final class InvalidCacheLoadException extends RuntimeException { |
| public InvalidCacheLoadException(String message) { |
| super(message); |
| } |
| } |
| } |
| |