com.amazonaws.services.dynamodbv2.datamodeling.internal

Class TTLCache<T>

java.lang.Object

com.amazonaws.services.dynamodbv2.datamodeling.internal.TTLCache<T>

Type Parameters:

T - value type

@ThreadSafe
public final class TTLCache<T>
extends java.lang.Object

A cache, backed by an LRUCache, that uses a loader to calculate values on cache miss or expired TTL.

Note that this cache does not proactively evict expired entries, however will immediately evict entries discovered to be expired on load.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	TTLCache.EntryLoader<T>

Constructor Summary

Constructors

Constructor and Description
TTLCache(int maxSize, long ttlInMillis, TTLCache.EntryLoader<T> loader)

Method Summary

Modifier and Type	Method and Description
void	clear() Clears all entries from the cache.
long	getLastUpdated(java.lang.String key) Get when the entry at this key was last updated.
int	getMaxSize() Returns the maximum size of the cache.
T	load(java.lang.String key) Uses the default loader to calculate the value at key and insert it into the cache, if it doesn't already exist or is expired according to the TTL.
T	load(java.lang.String key, java.util.function.Function<java.lang.String,T> f) Uses the inputted function to calculate the value at key and insert it into the cache, if it doesn't already exist or is expired according to the TTL.
T	put(java.lang.String key, T value) Put a new entry in the cache.
int	size() Returns the current size of the cache.
java.lang.String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

TTLCache

public TTLCache(int maxSize,
                long ttlInMillis,
                TTLCache.EntryLoader<T> loader)

Parameters:

maxSize - the maximum number of entries of the cache

ttlInMillis - the time to live value for entries of the cache, in milliseconds

Method Detail

load

public T load(java.lang.String key)

Uses the default loader to calculate the value at key and insert it into the cache, if it doesn't already exist or is expired according to the TTL.

This immediately evicts entries past the TTL such that a load failure results in the removal of the entry.

Entries that are not expired according to the TTL are returned without recalculating the value.

Within a grace period past the TTL, the cache may either return the cached value without recalculating or use the loader to recalculate the value. This is implemented such that, in a multi-threaded environment, only one thread per cache key uses the loader to recalculate the value at one time.

Parameters:

key - The cache key to load the value at

Returns:

The value of the given value (already existing or re-calculated).

load

public T load(java.lang.String key,
              java.util.function.Function<java.lang.String,T> f)

Uses the inputted function to calculate the value at key and insert it into the cache, if it doesn't already exist or is expired according to the TTL.

This immediately evicts entries past the TTL such that a load failure results in the removal of the entry.

Entries that are not expired according to the TTL are returned without recalculating the value.

Within a grace period past the TTL, the cache may either return the cached value without recalculating or use the loader to recalculate the value. This is implemented such that, in a multi-threaded environment, only one thread per cache key uses the loader to recalculate the value at one time.

Returns the value of the given key (already existing or re-calculated).

Parameters:

key - The cache key to load the value at

f - The function to use to load the value, given key as input

Returns:

The value of the given value (already existing or re-calculated).

put

public T put(java.lang.String key,
             T value)

Put a new entry in the cache. Returns the value previously at that key in the cache, or null if the entry previously didn't exist or is expired.

getLastUpdated

public long getLastUpdated(java.lang.String key)

Get when the entry at this key was last updated. Returns 0 if the entry doesn't exist at key.

size

public int size()

Returns the current size of the cache.

getMaxSize

public int getMaxSize()

Returns the maximum size of the cache.

clear

public void clear()

Clears all entries from the cache.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object