K
- the base key type for all caches created by this builder
V
- the base value type for all caches created by this builder
@GwtCompatible(emulated=true) public final class CacheBuilder<K,V> extends Object
A builder of LoadingCache
and Cache
instances having any combination of the following features:
These features are all optional; caches can be created using all or none of them. By default cache instances created by CacheBuilder
will not perform any type of eviction.
Usage example:
LoadingCache<Key, Graph> graphs = CacheBuilder.newBuilder() .maximumSize(10000) .expireAfterWrite(10, TimeUnit.MINUTES) .removalListener(MY_LISTENER) .build( new CacheLoader<Key, Graph>() { public Graph load(Key key) throws AnyException { return createExpensiveGraph(key); } });
Or equivalently,
// In real life this would come from a command-line flag or config file String spec = "maximumSize=10000,expireAfterWrite=10m"; LoadingCache<Key, Graph> graphs = CacheBuilder.from(spec) .removalListener(MY_LISTENER) .build( new CacheLoader<Key, Graph>() { public Graph load(Key key) throws AnyException { return createExpensiveGraph(key); } });
The returned cache is implemented as a hash table with similar performance characteristics to ConcurrentHashMap
. It implements all optional operations of the LoadingCache
and Cache
interfaces. The asMap
view (and its collection views) have weakly consistent iterators. This means that they are safe for concurrent use, but if other threads modify the cache after the iterator is created, it is undefined which of these changes, if any, are reflected in that iterator. These iterators never throw ConcurrentModificationException
.
Note: by default, the returned cache uses equality comparisons (the equals
method) to determine equality for keys or values. However, if weakKeys()
was specified, the cache uses identity (==
) comparisons instead for keys. Likewise, if weakValues()
or softValues()
was specified, the cache uses identity comparisons for values.
Entries are automatically evicted from the cache when any of maximumSize, maximumWeight, expireAfterWrite, expireAfterAccess, weakKeys, weakValues, or softValues are requested.
If maximumSize or maximumWeight is requested entries may be evicted on each cache modification.
If expireAfterWrite or expireAfterAccess is requested entries may be evicted on each cache modification, on occasional cache accesses, or on calls to Cache
. Expired entries may be counted by Cache
, but will never be visible to read or write operations.
If weakKeys, weakValues, or softValues are requested, it is possible for a key or value present in the cache to be reclaimed by the garbage collector. Entries with reclaimed keys or values may be removed from the cache on each cache modification, on occasional cache accesses, or on calls to Cache
; such entries may be counted in Cache
, but will never be visible to read or write operations.
Certain cache configurations will result in the accrual of periodic maintenance tasks which will be performed during write operations, or during occasional read operations in the absence of writes. The Cache
method of the returned cache will also perform maintenance, but calling it should not be necessary with a high throughput cache. Only caches built with removalListener, expireAfterWrite, expireAfterAccess, weakKeys, weakValues, or softValues perform periodic maintenance.
The caches produced by CacheBuilder
are serializable, and the deserialized caches retain all the configuration properties of the original cache. Note that the serialized form does not include cache contents, but only configuration.
See the Guava User Guide article on caching for a higher-level explanation.
Modifier and Type | Method and Description |
---|---|
<K1 extends K |
build()
Builds a cache which does not automatically load values when keys are requested.
|
<K1 extends K |
build(CacheLoader
Builds a cache, which either returns an already-loaded value for a given key or atomically computes or retrieves it using the supplied
CacheLoader .
|
CacheBuilder |
concurrencyLevel(int concurrencyLevel)
Guides the allowed concurrency among update operations.
|
CacheBuilder |
expireAfterAccess(long duration, TimeUnit
Specifies that each entry should be automatically removed from the cache once a fixed duration has elapsed after the entry's creation, the most recent replacement of its value, or its last access.
|
CacheBuilder |
expireAfterWrite(long duration, TimeUnit
Specifies that each entry should be automatically removed from the cache once a fixed duration has elapsed after the entry's creation, or the most recent replacement of its value.
|
static CacheBuilder |
from(CacheBuilderSpec
Constructs a new
CacheBuilder instance with the settings specified in
spec .
|
static CacheBuilder |
from(String
Constructs a new
CacheBuilder instance with the settings specified in
spec .
|
CacheBuilder |
initialCapacity(int initialCapacity)
Sets the minimum total size for the internal hash tables.
|
CacheBuilder |
maximumSize(long size)
Specifies the maximum number of entries the cache may contain.
|
CacheBuilder |
maximumWeight(long weight)
Specifies the maximum weight of entries the cache may contain.
|
static CacheBuilder |
newBuilder()
Constructs a new
CacheBuilder instance with default settings, including strong keys, strong values, and no automatic eviction of any kind.
|
CacheBuilder |
recordStats()
Enable the accumulation of
CacheStats during the operation of the cache.
|
CacheBuilder |
refreshAfterWrite(long duration, TimeUnit
Specifies that active entries are eligible for automatic refresh once a fixed duration has elapsed after the entry's creation, or the most recent replacement of its value.
|
<K1 extends K |
removalListener(RemovalListener
Specifies a listener instance that caches should notify each time an entry is removed for any
reason.
|
CacheBuilder |
softValues()
Specifies that each value (not key) stored in the cache should be wrapped in a
SoftReference (by default, strong references are used).
|
CacheBuilder |
ticker(Ticker
Specifies a nanosecond-precision time source for this cache.
|
String |
toString()
Returns a string representation for this CacheBuilder instance.
|
CacheBuilder |
weakKeys()
Specifies that each key (not value) stored in the cache should be wrapped in a
WeakReference (by default, strong references are used).
|
CacheBuilder |
weakValues()
Specifies that each value (not key) stored in the cache should be wrapped in a
WeakReference (by default, strong references are used).
|
<K1 extends K |
weigher(Weigher
Specifies the weigher to use in determining the weight of entries.
|
public static CacheBuilder<Object ,Object > newBuilder()
CacheBuilder
instance with default settings, including strong keys, strong values, and no automatic eviction of any kind.
@GwtIncompatible(value="To be supported") public static CacheBuilder<Object ,Object > from(CacheBuilderSpec spec)
CacheBuilder
instance with the settings specified in
spec
.
@GwtIncompatible(value="To be supported") public static CacheBuilder<Object ,Object > from(String spec)
CacheBuilder
instance with the settings specified in
spec
. This is especially useful for command-line configuration of a
CacheBuilder
.
spec
- a String in the format specified by
CacheBuilderSpec
public CacheBuilder<K ,V> initialCapacity(int initialCapacity)
60
, and the concurrency level is
8
, then eight segments are created, each having a hash table of size eight. Providing a large enough estimate at construction time avoids the need for expensive resizing operations later, but setting this value unnecessarily high wastes memory.
IllegalArgumentException
- if
initialCapacity
is negative
IllegalStateException
- if an initial capacity was already set
public CacheBuilder<K ,V> concurrencyLevel(int concurrencyLevel)
Defaults to 4. Note:The default may change in the future. If you care about this value, you should always choose it explicitly.
The current implementation uses the concurrency level to create a fixed number of hashtable segments, each governed by its own write lock. The segment lock is taken once for each explicit write, and twice for each cache loading computation (once prior to loading the new value, and once after loading completes). Much internal cache management is performed at the segment granularity. For example, access queues and write queues are kept per segment when they are required by the selected eviction algorithm. As such, when writing unit tests it is not uncommon to specify concurrencyLevel(1)
in order to achieve more deterministic eviction behavior.
Note that future implementations may abandon segment locking in favor of more advanced concurrency controls.
IllegalArgumentException
- if
concurrencyLevel
is nonpositive
IllegalStateException
- if a concurrency level was already set
public CacheBuilder<K ,V> maximumSize(long size)
When size
is zero, elements will be evicted immediately after being loaded into the cache. This can be useful in testing, or to disable caching temporarily without a code change.
This feature cannot be used in conjunction with maximumWeight
.
size
- the maximum size of the cache
IllegalArgumentException
- if
size
is negative
IllegalStateException
- if a maximum size or weight was already set
@GwtIncompatible(value="To be supported") public CacheBuilder<K ,V> maximumWeight(long weight)
Weigher
specified with
weigher
, and use of this method requires a corresponding call to
weigher
prior to calling
build(com.google.common.cache.CacheLoader<? super K1, V1>)
.
Note that the cache may evict an entry before this limit is exceeded. As the cache size grows close to the maximum, the cache evicts entries that are less likely to be used again. For example, the cache may evict an entry because it hasn't been used recently or very often.
When weight
is zero, elements will be evicted immediately after being loaded into cache. This can be useful in testing, or to disable caching temporarily without a code change.
Note that weight is only used to determine whether the cache is over capacity; it has no effect on selecting which entry should be evicted next.
This feature cannot be used in conjunction with maximumSize
.
weight
- the maximum total weight of entries the cache may contain
IllegalArgumentException
- if
weight
is negative
IllegalStateException
- if a maximum weight or size was already set
@GwtIncompatible(value="To be supported") public <K1 extends K,V1 extends V> CacheBuilder <K1 ,V1> weigher(Weigher <? super K1 ,? super V1> weigher)
maximumWeight(long)
when determining which entries to evict, and use of this method requires a corresponding call to
maximumWeight(long)
prior to calling
build(com.google.common.cache.CacheLoader<? super K1, V1>)
. Weights are measured and recorded when entries are inserted into the cache, and are thus effectively static during the lifetime of a cache entry.
When the weight of an entry is zero it will not be considered for size-based eviction (though it still may be evicted by other means).
Important note: Instead of returning this as a CacheBuilder
instance, this method returns CacheBuilder<K1, V1>
. From this point on, either the original reference or the returned reference may be used to complete configuration and build the cache, but only the "generic" one is type-safe. That is, it will properly prevent you from building caches whose key or value types are incompatible with the types accepted by the weigher already provided; the CacheBuilder
type cannot do this. For best results, simply use the standard method-chaining idiom, as illustrated in the documentation at top, configuring a CacheBuilder
and building your Cache
all in a single statement.
Warning: if you ignore the above advice, and use this CacheBuilder
to build a cache whose key or value type is incompatible with the weigher, you will likely experience a ClassCastException
at some undefined point in the future.
weigher
- the weigher to use in calculating the weight of cache entries
IllegalArgumentException
- if
size
is negative
IllegalStateException
- if a maximum size was already set
@GwtIncompatible(value="java.lang.ref.WeakReference") public CacheBuilder<K ,V> weakKeys()
WeakReference
(by default, strong references are used).
Warning: when this method is used, the resulting cache will use identity (==
) comparison to determine equality of keys.
Entries with keys that have been garbage collected may be counted in Cache
, but will never be visible to read or write operations; such entries are cleaned up as part of the routine maintenance described in the class javadoc.
IllegalStateException
- if the key strength was already set
@GwtIncompatible(value="java.lang.ref.WeakReference") public CacheBuilder<K ,V> weakValues()
WeakReference
(by default, strong references are used).
Weak values will be garbage collected once they are weakly reachable. This makes them a poor candidate for caching; consider softValues()
instead.
Note: when this method is used, the resulting cache will use identity (==
) comparison to determine equality of values.
Entries with values that have been garbage collected may be counted in Cache
, but will never be visible to read or write operations; such entries are cleaned up as part of the routine maintenance described in the class javadoc.
IllegalStateException
- if the value strength was already set
@GwtIncompatible(value="java.lang.ref.SoftReference") public CacheBuilder<K ,V> softValues()
SoftReference
(by default, strong references are used). Softly-referenced objects will be garbage-collected in a
globally least-recently-used manner, in response to memory demand.
Warning: in most circumstances it is better to set a per-cache maximum size instead of using soft references. You should only use this method if you are well familiar with the practical consequences of soft references.
Note: when this method is used, the resulting cache will use identity (==
) comparison to determine equality of values.
Entries with values that have been garbage collected may be counted in Cache
, but will never be visible to read or write operations; such entries are cleaned up as part of the routine maintenance described in the class javadoc.
IllegalStateException
- if the value strength was already set
public CacheBuilder<K ,V> expireAfterWrite(long duration, TimeUnit unit)
When duration
is zero, this method hands off to maximumSize
(0)
, ignoring any otherwise-specificed maximum size or weight. This can be useful in testing, or to disable caching temporarily without a code change.
Expired entries may be counted in Cache
, but will never be visible to read or write operations. Expired entries are cleaned up as part of the routine maintenance described in the class javadoc.
duration
- the length of time after an entry is created that it should be automatically removed
unit
- the unit that
duration
is expressed in
IllegalArgumentException
- if
duration
is negative
IllegalStateException
- if the time to live or time to idle was already set
public CacheBuilder<K ,V> expireAfterAccess(long duration, TimeUnit unit)
Cache.asMap().get(Object)
and
Cache.asMap().put(K, V)
), but not by operations on the collection-views of
Cache.asMap()
.
When duration
is zero, this method hands off to maximumSize
(0)
, ignoring any otherwise-specificed maximum size or weight. This can be useful in testing, or to disable caching temporarily without a code change.
Expired entries may be counted in Cache
, but will never be visible to read or write operations. Expired entries are cleaned up as part of the routine maintenance described in the class javadoc.
duration
- the length of time after an entry is last accessed that it should be automatically removed
unit
- the unit that
duration
is expressed in
IllegalArgumentException
- if
duration
is negative
IllegalStateException
- if the time to idle or time to live was already set
@GwtIncompatible(value="To be supported (synchronously).") public CacheBuilder<K ,V> refreshAfterWrite(long duration, TimeUnit unit)
LoadingCache.refresh(K)
, and are performed by calling
CacheLoader.reload(K, V)
.
As the default implementation of CacheLoader
is synchronous, it is recommended that users of this method override CacheLoader
with an asynchronous implementation; otherwise refreshes will be performed during unrelated cache read and write operations.
Currently automatic refreshes are performed when the first stale request for an entry occurs. The request triggering refresh will make a blocking call to CacheLoader
and immediately return the new value if the returned future is complete, and the old value otherwise.
Note: all exceptions thrown during refresh will be logged and then swallowed.
duration
- the length of time after an entry is created that it should be considered stale, and thus eligible for refresh
unit
- the unit that
duration
is expressed in
IllegalArgumentException
- if
duration
is negative
IllegalStateException
- if the refresh interval was already set
public CacheBuilder<K ,V> ticker(Ticker ticker)
System.nanoTime()
is used.
The primary intent of this method is to facilitate testing of caches with a fake or mock time source.
IllegalStateException
- if a ticker was already set
public <K1 extends K,V1 extends V> CacheBuilder <K1 ,V1> removalListener(RemovalListener <? super K1 ,? super V1> listener)
Warning: after invoking this method, do not continue to use this cache builder reference; instead use the reference this method returns. At runtime, these point to the same instance, but only the returned reference has the correct generic type information so as to ensure type safety. For best results, use the standard method-chaining idiom illustrated in the class documentation above, configuring a builder and building your cache in a single statement. Failure to heed this advice can result in a ClassCastException
being thrown by a cache operation at some undefined point in the future.
Warning: any exception thrown by listener
will not be propagated to the Cache
user, only logged via a Logger
.
this
for any remaining configuration and cache building
IllegalStateException
- if a removal listener was already set
public CacheBuilder<K ,V> recordStats()
CacheStats
during the operation of the cache. Without this
Cache.stats()
will return zero for all statistics. Note that recording stats requires bookkeeping to be performed with each operation, and thus imposes a performance penalty on cache operation.
public <K1 extends K,V1 extends V> LoadingCache <K1 ,V1> build(CacheLoader <? super K1 ,V1> loader)
CacheLoader
. If another thread is currently loading the value for this key, simply waits for that thread to finish and returns its loaded value. Note that multiple threads can concurrently load values for distinct keys.
This method does not alter the state of this CacheBuilder
instance, so it can be invoked again to create multiple independent caches.
loader
- the cache loader used to obtain new values
public <K1 extends K,V1 extends V> Cache <K1 ,V1> build()
Consider build(CacheLoader)
instead, if it is feasible to implement a CacheLoader
.
This method does not alter the state of this CacheBuilder
instance, so it can be invoked again to create multiple independent caches.
public StringtoString()