https://github.com/spring-projects/spring-framework: Spring Context (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2019 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;

import java.util.concurrent.Callable;

import org.springframework.lang.Nullable;


Interface that defines common cache operations.
Note: Due to the generic use of caching, it is recommended that
implementations allow storage of null values (for example to cache methods that return null). 
Author:Costin Leau, Juergen Hoeller, Stephane Nicoll
Since:3.1
/**
 * Interface that defines common cache operations.
 *
 * <b>Note:</b> Due to the generic use of caching, it is recommended that
 * implementations allow storage of <tt>null</tt> values (for example to
 * cache methods that return {@code null}).
 *
 * @author Costin Leau
 * @author Juergen Hoeller
 * @author Stephane Nicoll
 * @since 3.1
 */
public interface Cache {

	
Return the cache name.

/**
	 * Return the cache name.
	 */
	String getName();

	
Return the underlying native cache provider.

/**
	 * Return the underlying native cache provider.
	 */
	Object getNativeCache();

	
Return the value to which this cache maps the specified key.

Returns null if the cache contains no mapping for this key; otherwise, the cached value (which may be null itself) will be returned in a ValueWrapper. 
Params:
  • key – the key whose associated value is to be returned
See Also:
Returns:the value to which this cache maps the specified key, contained within a ValueWrapper which may also hold a cached null value. A straight null being returned means that the cache contains no mapping for this key.
/**
	 * Return the value to which this cache maps the specified key.
	 * <p>Returns {@code null} if the cache contains no mapping for this key;
	 * otherwise, the cached value (which may be {@code null} itself) will
	 * be returned in a {@link ValueWrapper}.
	 * @param key the key whose associated value is to be returned
	 * @return the value to which this cache maps the specified key,
	 * contained within a {@link ValueWrapper} which may also hold
	 * a cached {@code null} value. A straight {@code null} being
	 * returned means that the cache contains no mapping for this key.
	 * @see #get(Object, Class)
	 * @see #get(Object, Callable)
	 */
	@Nullable
	ValueWrapper get(Object key);

	
Return the value to which this cache maps the specified key,
generically specifying a type that return value will be cast to.

Note: This variant of get does not allow for differentiating between a cached null value and no cache entry found at all. Use the standard get(Object) variant for that purpose instead. 
Params:
  • key – the key whose associated value is to be returned
  • type – the required type of the returned value (may be null to bypass a type check; in case of a null value found in the cache, the specified type is irrelevant)
Throws:
See Also:
Returns:the value to which this cache maps the specified key (which may be null itself), or also null if the cache contains no mapping for this key
Since:4.0
/**
	 * Return the value to which this cache maps the specified key,
	 * generically specifying a type that return value will be cast to.
	 * <p>Note: This variant of {@code get} does not allow for differentiating
	 * between a cached {@code null} value and no cache entry found at all.
	 * Use the standard {@link #get(Object)} variant for that purpose instead.
	 * @param key the key whose associated value is to be returned
	 * @param type the required type of the returned value (may be
	 * {@code null} to bypass a type check; in case of a {@code null}
	 * value found in the cache, the specified type is irrelevant)
	 * @return the value to which this cache maps the specified key
	 * (which may be {@code null} itself), or also {@code null} if
	 * the cache contains no mapping for this key
	 * @throws IllegalStateException if a cache entry has been found
	 * but failed to match the specified type
	 * @since 4.0
	 * @see #get(Object)
	 */
	@Nullable
	<T> T get(Object key, @Nullable Class<T> type);

	
Return the value to which this cache maps the specified key, obtaining that value from valueLoader if necessary. This method provides a simple substitute for the conventional "if cached, return; otherwise create, cache and return" pattern. 
If possible, implementations should ensure that the loading operation is synchronized so that the specified valueLoader is only called once in case of concurrent access on the same key. 
If the valueLoader throws an exception, it is wrapped in a ValueRetrievalException 
Params:
  • key – the key whose associated value is to be returned
Throws:
See Also:
Returns:the value to which this cache maps the specified key
Since:4.3
/**
	 * Return the value to which this cache maps the specified key, obtaining
	 * that value from {@code valueLoader} if necessary. This method provides
	 * a simple substitute for the conventional "if cached, return; otherwise
	 * create, cache and return" pattern.
	 * <p>If possible, implementations should ensure that the loading operation
	 * is synchronized so that the specified {@code valueLoader} is only called
	 * once in case of concurrent access on the same key.
	 * <p>If the {@code valueLoader} throws an exception, it is wrapped in
	 * a {@link ValueRetrievalException}
	 * @param key the key whose associated value is to be returned
	 * @return the value to which this cache maps the specified key
	 * @throws ValueRetrievalException if the {@code valueLoader} throws an exception
	 * @since 4.3
	 * @see #get(Object)
	 */
	@Nullable
	<T> T get(Object key, Callable<T> valueLoader);

	
Associate the specified value with the specified key in this cache.

If the cache previously contained a mapping for this key, the old
value is replaced by the specified value.

Actual registration may be performed in an asynchronous or deferred fashion, with subsequent lookups possibly not seeing the entry yet. This may for example be the case with transactional cache decorators. Use putIfAbsent for guaranteed immediate registration. 
Params:
  • key – the key with which the specified value is to be associated
  • value – the value to be associated with the specified key
See Also:
/**
	 * Associate the specified value with the specified key in this cache.
	 * <p>If the cache previously contained a mapping for this key, the old
	 * value is replaced by the specified value.
	 * <p>Actual registration may be performed in an asynchronous or deferred
	 * fashion, with subsequent lookups possibly not seeing the entry yet.
	 * This may for example be the case with transactional cache decorators.
	 * Use {@link #putIfAbsent} for guaranteed immediate registration.
	 * @param key the key with which the specified value is to be associated
	 * @param value the value to be associated with the specified key
	 * @see #putIfAbsent(Object, Object)
	 */
	void put(Object key, @Nullable Object value);

	
Atomically associate the specified value with the specified key in this cache
if it is not set already.

This is equivalent to:


ValueWrapper existingValue = cache.get(key);
if (existingValue == null) {
    cache.put(key, value);
}
return existingValue;

 except that the action is performed atomically. While all out-of-the-box CacheManager implementations are able to perform the put atomically, the operation may also be implemented in two steps, e.g. with a check for presence and a subsequent put, in a non-atomic way. Check the documentation of the native cache implementation that you are using for more details. 
The default implementation delegates to get(Object) and put(Object, Object) along the lines of the code snippet above. 
Params:
  • key – the key with which the specified value is to be associated
  • value – the value to be associated with the specified key
See Also:
Returns:the value to which this cache maps the specified key (which may be null itself), or also null if the cache did not contain any mapping for that key prior to this call. Returning null is therefore an indicator that the given value has been associated with the key.
Since:4.1
/**
	 * Atomically associate the specified value with the specified key in this cache
	 * if it is not set already.
	 * <p>This is equivalent to:
	 * <pre><code>
	 * ValueWrapper existingValue = cache.get(key);
	 * if (existingValue == null) {
	 *     cache.put(key, value);
	 * }
	 * return existingValue;
	 * </code></pre>
	 * except that the action is performed atomically. While all out-of-the-box
	 * {@link CacheManager} implementations are able to perform the put atomically,
	 * the operation may also be implemented in two steps, e.g. with a check for
	 * presence and a subsequent put, in a non-atomic way. Check the documentation
	 * of the native cache implementation that you are using for more details.
	 * <p>The default implementation delegates to {@link #get(Object)} and
	 * {@link #put(Object, Object)} along the lines of the code snippet above.
	 * @param key the key with which the specified value is to be associated
	 * @param value the value to be associated with the specified key
	 * @return the value to which this cache maps the specified key (which may be
	 * {@code null} itself), or also {@code null} if the cache did not contain any
	 * mapping for that key prior to this call. Returning {@code null} is therefore
	 * an indicator that the given {@code value} has been associated with the key.
	 * @since 4.1
	 * @see #put(Object, Object)
	 */
	@Nullable
	default ValueWrapper putIfAbsent(Object key, @Nullable Object value) {
		ValueWrapper existingValue = get(key);
		if (existingValue == null) {
			put(key, value);
		}
		return existingValue;
	}

	
Evict the mapping for this key from this cache if it is present.

Actual eviction may be performed in an asynchronous or deferred fashion, with subsequent lookups possibly still seeing the entry. This may for example be the case with transactional cache decorators. Use evictIfPresent for guaranteed immediate removal. 
Params:
  • key – the key whose mapping is to be removed from the cache
See Also:
/**
	 * Evict the mapping for this key from this cache if it is present.
	 * <p>Actual eviction may be performed in an asynchronous or deferred
	 * fashion, with subsequent lookups possibly still seeing the entry.
	 * This may for example be the case with transactional cache decorators.
	 * Use {@link #evictIfPresent} for guaranteed immediate removal.
	 * @param key the key whose mapping is to be removed from the cache
	 * @see #evictIfPresent(Object)
	 */
	void evict(Object key);

	
Evict the mapping for this key from this cache if it is present,
expecting the key to be immediately invisible for subsequent lookups.

The default implementation delegates to evict(Object), returning false for not-determined prior presence of the key. Cache providers and in particular cache decorators are encouraged to perform immediate eviction if possible (e.g. in case of generally deferred cache operations within a transaction) and to reliably determine prior presence of the given key. 
Params:
  • key – the key whose mapping is to be removed from the cache
See Also:
Returns:true if the cache was known to have a mapping for this key before, false if it did not (or if prior presence could not be determined)
Since:5.2
/**
	 * Evict the mapping for this key from this cache if it is present,
	 * expecting the key to be immediately invisible for subsequent lookups.
	 * <p>The default implementation delegates to {@link #evict(Object)},
	 * returning {@code false} for not-determined prior presence of the key.
	 * Cache providers and in particular cache decorators are encouraged
	 * to perform immediate eviction if possible (e.g. in case of generally
	 * deferred cache operations within a transaction) and to reliably
	 * determine prior presence of the given key.
	 * @param key the key whose mapping is to be removed from the cache
	 * @return {@code true} if the cache was known to have a mapping for
	 * this key before, {@code false} if it did not (or if prior presence
	 * could not be determined)
	 * @since 5.2
	 * @see #evict(Object)
	 */
	default boolean evictIfPresent(Object key) {
		evict(key);
		return false;
	}

	
Clear the cache through removing all mappings.

Actual clearing may be performed in an asynchronous or deferred fashion, with subsequent lookups possibly still seeing the entries. This may for example be the case with transactional cache decorators. Use invalidate() for guaranteed immediate removal of entries. 
See Also:
/**
	 * Clear the cache through removing all mappings.
	 * <p>Actual clearing may be performed in an asynchronous or deferred
	 * fashion, with subsequent lookups possibly still seeing the entries.
	 * This may for example be the case with transactional cache decorators.
	 * Use {@link #invalidate()} for guaranteed immediate removal of entries.
	 * @see #invalidate()
	 */
	void clear();

	
Invalidate the cache through removing all mappings, expecting all
entries to be immediately invisible for subsequent lookups.

See Also:
Returns:true if the cache was known to have mappings before, false if it did not (or if prior presence of entries could not be determined)
Since:5.2
/**
	 * Invalidate the cache through removing all mappings, expecting all
	 * entries to be immediately invisible for subsequent lookups.
	 * @return {@code true} if the cache was known to have mappings before,
	 * {@code false} if it did not (or if prior presence of entries could
	 * not be determined)
	 * @since 5.2
	 * @see #clear()
	 */
	default boolean invalidate() {
		clear();
		return false;
	}


	
A (wrapper) object representing a cache value.

/**
	 * A (wrapper) object representing a cache value.
	 */
	@FunctionalInterface
	interface ValueWrapper {

		
Return the actual value in the cache.

/**
		 * Return the actual value in the cache.
		 */
		@Nullable
		Object get();
	}


	
Wrapper exception to be thrown from Cache.get(Object, Callable<Object>) in case of the value loader callback failing with an exception. 
Since:4.3
/**
	 * Wrapper exception to be thrown from {@link #get(Object, Callable)}
	 * in case of the value loader callback failing with an exception.
	 * @since 4.3
	 */
	@SuppressWarnings("serial")
	class ValueRetrievalException extends RuntimeException {

		@Nullable
		private final Object key;

		public ValueRetrievalException(@Nullable Object key, Callable<?> loader, Throwable ex) {
			super(String.format("Value for key '%s' could not be loaded using '%s'", key, loader), ex);
			this.key = key;
		}

		@Nullable
		public Object getKey() {
			return this.key;
		}
	}

}