com.hazelcast.com.google.common.cache.CacheLoader Maven / Gradle / Ivy
/*
* 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.hazelcast.com.google.common.cache;
import static com.hazelcast.com.google.common.base.Preconditions.checkNotNull;
import com.hazelcast.com.google.common.annotations.GwtCompatible;
import com.hazelcast.com.google.common.annotations.GwtIncompatible;
import com.hazelcast.com.google.common.base.Function;
import com.hazelcast.com.google.common.base.Supplier;
import com.hazelcast.com.google.common.util.concurrent.Futures;
import com.hazelcast.com.google.common.util.concurrent.ListenableFuture;
import com.hazelcast.com.google.common.util.concurrent.ListenableFutureTask;
import com.hazelcast.com.google.errorprone.annotations.CheckReturnValue;
import java.io.Serializable;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
/**
* Computes or retrieves values, based on a key, for use in populating a {@link LoadingCache}.
*
* Most implementations will only need to implement {@link #load}. Other methods may be
* overridden as desired.
*
*
Usage example:
*
*
{@code
* CacheLoader loader = new CacheLoader() {
* public Graph load(Key key) throws AnyException {
* return createExpensiveGraph(key);
* }
* };
* LoadingCache cache = CacheBuilder.newBuilder().build(loader);
* }
*
* Since this example doesn't support reloading or bulk loading, it can also be specified much
* more simply:
*
*
{@code
* CacheLoader loader = CacheLoader.from(key -> createExpensiveGraph(key));
* }
*
* @author Charles Fry
* @since 10.0
*/
@GwtCompatible(emulated = true)
public abstract class CacheLoader {
/** 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}; must not be null
* @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 a replacement value corresponding to an already-cached {@code key}. This
* method is called when an existing cache entry is refreshed by {@link
* CacheBuilder#refreshAfterWrite}, or through a call to {@link LoadingCache#refresh}.
*
* This implementation synchronously delegates to {@link #load}. It is recommended that it be
* overridden with an asynchronous implementation when using {@link
* CacheBuilder#refreshAfterWrite}.
*
*
Note: all exceptions thrown by this method will be logged and then swallowed.
*
* @param key the non-null key whose value should be loaded
* @param oldValue the non-null old value corresponding to {@code key}
* @return the future new value associated with {@code key}; must not be null, must not return
* null
* @throws Exception if unable to reload 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
*/
@GwtIncompatible // Futures
public ListenableFuture reload(K key, V oldValue) throws Exception {
checkNotNull(key);
checkNotNull(oldValue);
return Futures.immediateFuture(load(key));
}
/**
* Computes or retrieves the values corresponding to {@code keys}. This method is called by {@link
* LoadingCache#getAll}.
*
* 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}.
*
*
This method should be overridden 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 overridden.
*
* @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; may not
* contain null values
* @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 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 that uses {@code function} to load keys, without supporting either
* reloading or bulk loading. This allows creating a cache loader using a lambda expression.
*
* @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}
*/
@CheckReturnValue
public static CacheLoader from(Function function) {
return new FunctionToCacheLoader<>(function);
}
/**
* Returns a cache loader based on an existing supplier instance. Note that there's no need
* to create a new 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
*/
@CheckReturnValue
public static CacheLoader