com.google.common.cache
Class CacheLoader<K,V>

java.lang.Object
  extended by com.google.common.cache.CacheLoader<K,V>

@GwtCompatible(emulated=true)
public abstract class CacheLoader<K,V>
extends Object

Computes or retrieves values, based on a key, for use in populating a LoadingCache.

Most implementations will only need to implement load(K). Other methods may be overridden as desired.

Since:
10.0
Author:
Charles Fry

Nested Class Summary
static class CacheLoader.InvalidCacheLoadException
          Thrown to indicate that an invalid response was returned from a call to CacheLoader.
 
Constructor Summary
protected CacheLoader()
          Constructor for use by subclasses.
 
Method Summary
static
<K,V> CacheLoader<K,V>
from(Function<K,V> function)
          Returns a cache loader based on an existing function instance.
static
<V> CacheLoader<Object,V>
from(Supplier<V> supplier)
          Returns a cache loader based on an existing supplier instance.
abstract  V load(K key)
          Computes or retrieves the value corresponding to key.
 Map<K,V> loadAll(Iterable<? extends K> keys)
          Computes or retrieves the values corresponding to keys.
 ListenableFuture<V> reload(K key, V oldValue)
          Computes or retrieves a replacement value corresponding to an already-cached key.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

CacheLoader

protected CacheLoader()
Constructor for use by subclasses.

Method Detail

load

public abstract V load(K key)
                throws Exception
Computes or retrieves the value corresponding to key.

Parameters:
key - the non-null key whose value should be loaded
Returns:
the value associated with key; must not be null
Throws:
CacheLoader.InvalidCacheLoadException - if unable to load the result
InterruptedException - if this method is interrupted. InterruptedException is treated like any other Exception in all respects except that, when it is caught, the thread's interrupt status is set
Exception

reload

@GwtIncompatible(value="Futures")
public ListenableFuture<V> reload(K key,
                                                       V oldValue)
                           throws Exception
Computes or retrieves a replacement value corresponding to an already-cached key. This method is called when an existing cache entry is refreshed by CacheBuilder.refreshAfterWrite(long, java.util.concurrent.TimeUnit), or through a call to LoadingCache.refresh(K).

This implementation synchronously delegates to load(K). It is recommended that it be overridden with an asynchronous implementation when using CacheBuilder.refreshAfterWrite(long, java.util.concurrent.TimeUnit).

Note: all exceptions thrown by this method will be logged and then swallowed.

Parameters:
key - the non-null key whose value should be loaded
oldValue - the non-null old value corresponding to key
Returns:
the future new value associated with key; must not be null, must not return null
Throws:
CacheLoader.InvalidCacheLoadException - if unable to reload the result
InterruptedException - if this method is interrupted. InterruptedException is treated like any other Exception in all respects except that, when it is caught, the thread's interrupt status is set
Exception
Since:
11.0

loadAll

public Map<K,V> loadAll(Iterable<? extends K> keys)
                 throws Exception
Computes or retrieves the values corresponding to keys. This method is called by LoadingCache.getAll(java.lang.Iterable).

If the returned map doesn't contain all requested keys then the entries it does contain will be cached, but getAll will throw an exception. If the returned map contains extra keys not present in keys then all returned entries will be cached, but only the entries for keys will be returned from getAll.

This method should be overriden when bulk retrieval is significantly more efficient than many individual lookups. Note that LoadingCache.getAll(java.lang.Iterable) will defer to individual calls to LoadingCache.get(K) if this method is not overriden.

Parameters:
keys - the unique, non-null keys whose values should be loaded
Returns:
a map from each key in keys to the value associated with that key; may not contain null values
Throws:
CacheLoader.InvalidCacheLoadException - if unable to load the result
InterruptedException - if this method is interrupted. InterruptedException is treated like any other Exception in all respects except that, when it is caught, the thread's interrupt status is set
Exception
Since:
11.0

from

@Beta
public static <K,V> CacheLoader<K,V> from(Function<K,V> function)
Returns a cache loader based on an existing function instance. Note that there's no need to create a new function just to pass it in here; just subclass CacheLoader and implement load instead.

Parameters:
function - the function to be used for loading values; must never return null
Returns:
a cache loader that loads values by passing each key to function

from

@Beta
public static <V> CacheLoader<Object,V> from(Supplier<V> supplier)
Returns a cache loader based on an existing supplier instance. Note that there's no need to create a new supplier just to pass it in here; just subclass CacheLoader and implement load instead.

Parameters:
supplier - the supplier to be used for loading values; must never return null
Returns:
a cache loader that loads values by calling Supplier.get(), irrespective of the key


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