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 {@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
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.
* 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
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 {@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:
* 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 {@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 {@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 {@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.
* @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.
*/
@FunctionalInterface
interface ValueWrapper {
/**
* Return the actual value in the cache.
*/
@Nullable
Object get();
}
/**
* 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;
}
}
}
* 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.
*
* ValueWrapper existingValue = cache.get(key);
* if (existingValue == null) {
* cache.put(key, value);
* }
* return existingValue;
*