/* * 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 com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.base.Function; import com.google.common.collect.ImmutableMap; import com.google.common.util.concurrent.ExecutionError; import com.google.common.util.concurrent.UncheckedExecutionException; import java.util.concurrent.ConcurrentMap; import java.util.concurrent.ExecutionException; /** * A semi-persistent mapping from keys to values. Values are automatically loaded by the cache, * and are stored in the cache until either evicted or manually invalidated. * *
Implementations of this interface are expected to be thread-safe, and can be safely accessed * by multiple concurrent threads. * *
When evaluated as a {@link Function}, a cache yields the same result as invoking * {@link #getUnchecked}. * *
Note that while this class is still annotated as {@link Beta}, the API is frozen from a
* consumer's standpoint. In other words existing methods are all considered {@code non-Beta} and
* won't be changed without going through an 18 month deprecation cycle; however new methods may be
* added at any time.
*
* @author Charles Fry
* @since 11.0
*/
@Beta
@GwtCompatible
public interface LoadingCache If another call to {@link #get} or {@link #getUnchecked} is currently loading the value for
* {@code key}, simply waits for that thread to finish and returns its loaded value. Note that
* multiple threads can concurrently load values for distinct keys.
*
* Caches loaded by a {@link CacheLoader} will call {@link CacheLoader#load} to load new values
* into the cache. Newly loaded values are added to the cache using
* {@code Cache.asMap().putIfAbsent} after loading has completed; if another value was associated
* with {@code key} while the new value was loading then a removal notification will be sent for
* the new value.
*
* If the cache loader associated with this cache is known not to throw checked
* exceptions, then prefer {@link #getUnchecked} over this method.
*
* @throws ExecutionException if a checked exception was thrown while loading the value. ({@code
* ExecutionException} is thrown even if
* computation was interrupted by an {@code InterruptedException}.)
* @throws UncheckedExecutionException if an unchecked exception was thrown while loading the
* value
* @throws ExecutionError if an error was thrown while loading the value
*/
V get(K key) throws ExecutionException;
/**
* Returns the value associated with {@code key} in this cache, first loading that value if
* necessary. No observable state associated with this cache is modified until loading
* completes. Unlike {@link #get}, this method does not throw a checked exception, and thus should
* only be used in situations where checked exceptions are not thrown by the cache loader.
*
* If another call to {@link #get} or {@link #getUnchecked} is currently loading the value for
* {@code key}, simply waits for that thread to finish and returns its loaded value. Note that
* multiple threads can concurrently load values for distinct keys.
*
* Caches loaded by a {@link CacheLoader} will call {@link CacheLoader#load} to load new values
* into the cache. Newly loaded values are added to the cache using
* {@code Cache.asMap().putIfAbsent} after loading has completed; if another value was associated
* with {@code key} while the new value was loading then a removal notification will be sent for
* the new value.
*
* Warning: this method silently converts checked exceptions to unchecked exceptions,
* and should not be used with cache loaders which throw checked exceptions. In such cases use
* {@link #get} instead.
*
* @throws UncheckedExecutionException if an exception was thrown while loading the value. (As
* explained in the last paragraph above, this should be an unchecked exception only.)
* @throws ExecutionError if an error was thrown while loading the value
*/
V getUnchecked(K key);
/**
* Returns a map of the values associated with {@code keys}, creating or retrieving those values
* if necessary. The returned map contains entries that were already cached, combined with newly
* loaded entries; it will never contain null keys or values.
*
* Caches loaded by a {@link CacheLoader} will issue a single request to
* {@link CacheLoader#loadAll} for all keys which are not already present in the cache. All
* entries returned by {@link CacheLoader#loadAll} will be stored in the cache, over-writing
* any previously cached values. This method will throw an exception if
* {@link CacheLoader#loadAll} returns {@code null}, returns a map containing null keys or values,
* or fails to return an entry for each requested key.
*
* Note that duplicate elements in {@code keys}, as determined by {@link Object#equals}, will
* be ignored.
*
* @throws ExecutionException if a checked exception was thrown while loading the value. ({@code
* ExecutionException} is thrown even if
* computation was interrupted by an {@code InterruptedException}.)
* @throws UncheckedExecutionException if an unchecked exception was thrown while loading the
* values
* @throws ExecutionError if an error was thrown while loading the values
* @since 11.0
*/
ImmutableMap Caches loaded by a {@link CacheLoader} will call {@link CacheLoader#reload} if the
* cache currently contains a value for {@code key}, and {@link CacheLoader#load} otherwise.
* Loading is asynchronous only if {@link CacheLoader#reload} was overridden with an
* asynchronous implementation.
*
* Returns without doing anything if another thread is currently loading the value for
* {@code key}. If the cache loader associated with this cache performs refresh asynchronously
* then this method may return before refresh completes.
*
* @since 11.0
*/
void refresh(K key);
/**
* {@inheritDoc}
*
* Note that although the view is modifiable, no method on the returned map will ever
* cause entries to be automatically loaded.
*/
@Override
ConcurrentMap