spring中的组合模式

org.springframework.cache.support.CompositeCacheManager

/*
 * Copyright 2002-2016 the original author or 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
 *
 *      https://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.springframework.cache.support;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.cache.Cache;
import org.springframework.cache.CacheManager;
import org.springframework.lang.Nullable;

/**
 * Composite {@link CacheManager} implementation that iterates over
 * a given collection of delegate {@link CacheManager} instances.
 *
 * <p>Allows {@link NoOpCacheManager} to be automatically added to the end of
 * the list for handling cache declarations without a backing store. Otherwise,
 * any custom {@link CacheManager} may play that role of the last delegate as
 * well, lazily creating cache regions for any requested name.
 *
 * <p>Note: Regular CacheManagers that this composite manager delegates to need
 * to return {@code null} from {@link #getCache(String)} if they are unaware of
 * the specified cache name, allowing for iteration to the next delegate in line.
 * However, most {@link CacheManager} implementations fall back to lazy creation
 * of named caches once requested; check out the specific configuration details
 * for a 'static' mode with fixed cache names, if available.
 *
 * @author Costin Leau
 * @author Juergen Hoeller
 * @since 3.1
 * @see #setFallbackToNoOpCache
 * @see org.springframework.cache.concurrent.ConcurrentMapCacheManager#setCacheNames
 */
public class CompositeCacheManager implements CacheManager, InitializingBean {

	private final List<CacheManager> cacheManagers = new ArrayList<>();

	private boolean fallbackToNoOpCache = false;

	/**
	 * Construct an empty CompositeCacheManager, with delegate CacheManagers to
	 * be added via the {@link #setCacheManagers "cacheManagers"} property.
	 */
	public CompositeCacheManager() {
	}

	/**
	 * Construct a CompositeCacheManager from the given delegate CacheManagers.
	 * @param cacheManagers the CacheManagers to delegate to
	 */
	public CompositeCacheManager(CacheManager... cacheManagers) {
		setCacheManagers(Arrays.asList(cacheManagers));
	}

	/**
	 * Specify the CacheManagers to delegate to.
	 */
	public void setCacheManagers(Collection<CacheManager> cacheManagers) {
		this.cacheManagers.addAll(cacheManagers);
	}

	/**
	 * Indicate whether a {@link NoOpCacheManager} should be added at the end of the delegate list.
	 * In this case, any {@code getCache} requests not handled by the configured CacheManagers will
	 * be automatically handled by the {@link NoOpCacheManager} (and hence never return {@code null}).
	 */
	public void setFallbackToNoOpCache(boolean fallbackToNoOpCache) {
		this.fallbackToNoOpCache = fallbackToNoOpCache;
	}

	@Override
	public void afterPropertiesSet() {
		if (this.fallbackToNoOpCache) {
			this.cacheManagers.add(new NoOpCacheManager());
		}
	}

	@Override
	@Nullable
	public Cache getCache(String name) {
		for (CacheManager cacheManager : this.cacheManagers) {
			Cache cache = cacheManager.getCache(name);
			if (cache != null) {
				return cache;
			}
		}
		return null;
	}

	@Override
	public Collection<String> getCacheNames() {
		Set<String> names = new LinkedHashSet<>();
		for (CacheManager manager : this.cacheManagers) {
			names.addAll(manager.getCacheNames());
		}
		return Collections.unmodifiableSet(names);
	}

}