https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2009 The Guava 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
 *
 * http://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 com.google.common.cache;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Ascii;
import com.google.common.base.Equivalence;
import com.google.common.base.MoreObjects;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.base.Ticker;
import com.google.common.cache.AbstractCache.SimpleStatsCounter;
import com.google.common.cache.AbstractCache.StatsCounter;
import com.google.common.cache.LocalCache.Strength;
import com.google.errorprone.annotations.CheckReturnValue;
import com.google.j2objc.annotations.J2ObjCIncompatible;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.ConcurrentModificationException;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.checkerframework.checker.nullness.qual.MonotonicNonNull;


A builder of LoadingCache and Cache instances having any combination of the following features: 
    
  
  • automatic loading of entries into the cache
  
  • least-recently-used eviction when a maximum size is exceeded
  
  • time-based expiration of entries, measured since last access or last write
  
  • keys automatically wrapped in weak references 
  • values automatically wrapped in weak or soft references 
  • notification of evicted (or otherwise removed) entries
  
  • accumulation of cache access statistics



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(Duration.ofMinutes(10))
    .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.cleanUp. Expired entries may be counted by Cache.size, 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.cleanUp; such entries may be counted in Cache.size, 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.cleanUp 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.

Author:Charles Fry, Kevin Bourrillion
Type parameters:
  • <K> – the most general key type this builder will be able to create caches for. This is normally Object unless it is constrained by using a method like 
    #removalListener
  • <V> – the most general value type this builder will be able to create caches for. This is normally Object unless it is constrained by using a method like 
    #removalListener
Since:10.0
/**
 * A builder of {@link LoadingCache} and {@link Cache} instances having any combination of the
 * following features:
 *
 * <ul>
 *   <li>automatic loading of entries into the cache
 *   <li>least-recently-used eviction when a maximum size is exceeded
 *   <li>time-based expiration of entries, measured since last access or last write
 *   <li>keys automatically wrapped in {@linkplain WeakReference weak} references
 *   <li>values automatically wrapped in {@linkplain WeakReference weak} or {@linkplain
 *       SoftReference soft} references
 *   <li>notification of evicted (or otherwise removed) entries
 *   <li>accumulation of cache access statistics
 * </ul>
 *
 *
 * <p>These features are all optional; caches can be created using all or none of them. By default
 * cache instances created by {@code CacheBuilder} will not perform any type of eviction.
 *
 * <p>Usage example:
 *
 * <pre>{@code
 * LoadingCache<Key, Graph> graphs = CacheBuilder.newBuilder()
 *     .maximumSize(10000)
 *     .expireAfterWrite(Duration.ofMinutes(10))
 *     .removalListener(MY_LISTENER)
 *     .build(
 *         new CacheLoader<Key, Graph>() {
 *           public Graph load(Key key) throws AnyException {
 *             return createExpensiveGraph(key);
 *           }
 *         });
 * }</pre>
 *
 * <p>Or equivalently,
 *
 * <pre>{@code
 * // 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);
 *           }
 *         });
 * }</pre>
 *
 * <p>The returned cache is implemented as a hash table with similar performance characteristics to
 * {@link ConcurrentHashMap}. It implements all optional operations of the {@link LoadingCache} and
 * {@link Cache} interfaces. The {@code asMap} view (and its collection views) have <i>weakly
 * consistent iterators</i>. 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 {@link
 * ConcurrentModificationException}.
 *
 * <p><b>Note:</b> by default, the returned cache uses equality comparisons (the {@link
 * Object#equals equals} method) to determine equality for keys or values. However, if {@link
 * #weakKeys} was specified, the cache uses identity ({@code ==}) comparisons instead for keys.
 * Likewise, if {@link #weakValues} or {@link #softValues} was specified, the cache uses identity
 * comparisons for values.
 *
 * <p>Entries are automatically evicted from the cache when any of {@linkplain #maximumSize(long)
 * maximumSize}, {@linkplain #maximumWeight(long) maximumWeight}, {@linkplain #expireAfterWrite
 * expireAfterWrite}, {@linkplain #expireAfterAccess expireAfterAccess}, {@linkplain #weakKeys
 * weakKeys}, {@linkplain #weakValues weakValues}, or {@linkplain #softValues softValues} are
 * requested.
 *
 * <p>If {@linkplain #maximumSize(long) maximumSize} or {@linkplain #maximumWeight(long)
 * maximumWeight} is requested entries may be evicted on each cache modification.
 *
 * <p>If {@linkplain #expireAfterWrite expireAfterWrite} or {@linkplain #expireAfterAccess
 * expireAfterAccess} is requested entries may be evicted on each cache modification, on occasional
 * cache accesses, or on calls to {@link Cache#cleanUp}. Expired entries may be counted by {@link
 * Cache#size}, but will never be visible to read or write operations.
 *
 * <p>If {@linkplain #weakKeys weakKeys}, {@linkplain #weakValues weakValues}, or {@linkplain
 * #softValues 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 {@link
 * Cache#cleanUp}; such entries may be counted in {@link Cache#size}, but will never be visible to
 * read or write operations.
 *
 * <p>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 {@link Cache#cleanUp} 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
 * {@linkplain #removalListener removalListener}, {@linkplain #expireAfterWrite expireAfterWrite},
 * {@linkplain #expireAfterAccess expireAfterAccess}, {@linkplain #weakKeys weakKeys}, {@linkplain
 * #weakValues weakValues}, or {@linkplain #softValues softValues} perform periodic maintenance.
 *
 * <p>The caches produced by {@code CacheBuilder} are serializable, and the deserialized caches
 * retain all the configuration properties of the original cache. Note that the serialized form does
 * <i>not</i> include cache contents, but only configuration.
 *
 * <p>See the Guava User Guide article on <a
 * href="https://github.com/google/guava/wiki/CachesExplained">caching</a> for a higher-level
 * explanation.
 *
 * @param <K> the most general key type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@code
 *     #removalListener}
 * @param <V> the most general value type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@code
 *     #removalListener}
 * @author Charles Fry
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible(emulated = true)
public final class CacheBuilder<K, V> {
  private static final int DEFAULT_INITIAL_CAPACITY = 16;
  private static final int DEFAULT_CONCURRENCY_LEVEL = 4;
  private static final int DEFAULT_EXPIRATION_NANOS = 0;
  private static final int DEFAULT_REFRESH_NANOS = 0;

  static final Supplier<? extends StatsCounter> NULL_STATS_COUNTER =
      Suppliers.ofInstance(
          new StatsCounter() {
            @Override
            public void recordHits(int count) {}

            @Override
            public void recordMisses(int count) {}

            @Override
            public void recordLoadSuccess(long loadTime) {}

            @Override
            public void recordLoadException(long loadTime) {}

            @Override
            public void recordEviction() {}

            @Override
            public CacheStats snapshot() {
              return EMPTY_STATS;
            }
          });
  static final CacheStats EMPTY_STATS = new CacheStats(0, 0, 0, 0, 0, 0);

  static final Supplier<StatsCounter> CACHE_STATS_COUNTER =
      new Supplier<StatsCounter>() {
        @Override
        public StatsCounter get() {
          return new SimpleStatsCounter();
        }
      };

  enum NullListener implements RemovalListener<Object, Object> {
    INSTANCE;

    @Override
    public void onRemoval(RemovalNotification<Object, Object> notification) {}
  }

  enum OneWeigher implements Weigher<Object, Object> {
    INSTANCE;

    @Override
    public int weigh(Object key, Object value) {
      return 1;
    }
  }

  static final Ticker NULL_TICKER =
      new Ticker() {
        @Override
        public long read() {
          return 0;
        }
      };

  private static final Logger logger = Logger.getLogger(CacheBuilder.class.getName());

  static final int UNSET_INT = -1;

  boolean strictParsing = true;

  int initialCapacity = UNSET_INT;
  int concurrencyLevel = UNSET_INT;
  long maximumSize = UNSET_INT;
  long maximumWeight = UNSET_INT;
  @MonotonicNonNull Weigher<? super K, ? super V> weigher;

  @MonotonicNonNull Strength keyStrength;
  @MonotonicNonNull Strength valueStrength;

  long expireAfterWriteNanos = UNSET_INT;
  long expireAfterAccessNanos = UNSET_INT;
  long refreshNanos = UNSET_INT;

  @MonotonicNonNull Equivalence<Object> keyEquivalence;
  @MonotonicNonNull Equivalence<Object> valueEquivalence;

  @MonotonicNonNull RemovalListener<? super K, ? super V> removalListener;
  @MonotonicNonNull Ticker ticker;

  Supplier<? extends StatsCounter> statsCounterSupplier = NULL_STATS_COUNTER;

  private CacheBuilder() {}

  
Constructs a new CacheBuilder instance with default settings, including strong keys, strong values, and no automatic eviction of any kind. 
Note that while this return type is CacheBuilder<Object, Object>, type parameters on the build methods allow you to create a cache of any key and value type desired. 
/**
   * Constructs a new {@code CacheBuilder} instance with default settings, including strong keys,
   * strong values, and no automatic eviction of any kind.
   *
   * <p>Note that while this return type is {@code CacheBuilder<Object, Object>}, type parameters on
   * the {@link #build} methods allow you to create a cache of any key and value type desired.
   */
  public static CacheBuilder<Object, Object> newBuilder() {
    return new CacheBuilder<>();
  }

  
Constructs a new CacheBuilder instance with the settings specified in spec. 
Since:12.0
/**
   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
   *
   * @since 12.0
   */
  @GwtIncompatible // To be supported
  public static CacheBuilder<Object, Object> from(CacheBuilderSpec spec) {
    return spec.toCacheBuilder().lenientParsing();
  }

  
Constructs a new CacheBuilder instance with the settings specified in spec. This is especially useful for command-line configuration of a CacheBuilder. 
Params:
Since:12.0
/**
   * Constructs a new {@code CacheBuilder} instance with the settings specified in {@code spec}.
   * This is especially useful for command-line configuration of a {@code CacheBuilder}.
   *
   * @param spec a String in the format specified by {@link CacheBuilderSpec}
   * @since 12.0
   */
  @GwtIncompatible // To be supported
  public static CacheBuilder<Object, Object> from(String spec) {
    return from(CacheBuilderSpec.parse(spec));
  }

  
Enables lenient parsing. Useful for tests and spec parsing.

Returns:this CacheBuilder instance (for chaining)
/**
   * Enables lenient parsing. Useful for tests and spec parsing.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   */
  @GwtIncompatible // To be supported
  CacheBuilder<K, V> lenientParsing() {
    strictParsing = false;
    return this;
  }

  
Sets a custom Equivalence strategy for comparing keys. 
By default, the cache uses Equivalence.identity to determine key equality when weakKeys is specified, and Equivalence.equals() otherwise. 
Returns:this CacheBuilder instance (for chaining)
/**
   * Sets a custom {@code Equivalence} strategy for comparing keys.
   *
   * <p>By default, the cache uses {@link Equivalence#identity} to determine key equality when
   * {@link #weakKeys} is specified, and {@link Equivalence#equals()} otherwise.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   */
  @GwtIncompatible // To be supported
  CacheBuilder<K, V> keyEquivalence(Equivalence<Object> equivalence) {
    checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);
    keyEquivalence = checkNotNull(equivalence);
    return this;
  }

  Equivalence<Object> getKeyEquivalence() {
    return MoreObjects.firstNonNull(keyEquivalence, getKeyStrength().defaultEquivalence());
  }

  
Sets a custom Equivalence strategy for comparing values. 
By default, the cache uses Equivalence.identity to determine value equality when weakValues or softValues is specified, and Equivalence.equals() otherwise. 
Returns:this CacheBuilder instance (for chaining)
/**
   * Sets a custom {@code Equivalence} strategy for comparing values.
   *
   * <p>By default, the cache uses {@link Equivalence#identity} to determine value equality when
   * {@link #weakValues} or {@link #softValues} is specified, and {@link Equivalence#equals()}
   * otherwise.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   */
  @GwtIncompatible // To be supported
  CacheBuilder<K, V> valueEquivalence(Equivalence<Object> equivalence) {
    checkState(
        valueEquivalence == null, "value equivalence was already set to %s", valueEquivalence);
    this.valueEquivalence = checkNotNull(equivalence);
    return this;
  }

  Equivalence<Object> getValueEquivalence() {
    return MoreObjects.firstNonNull(valueEquivalence, getValueStrength().defaultEquivalence());
  }

  
Sets the minimum total size for the internal hash tables. For example, if the initial capacity is 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. 
Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * Sets the minimum total size for the internal hash tables. For example, if the initial capacity
   * is {@code 60}, and the concurrency level is {@code 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.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code initialCapacity} is negative
   * @throws IllegalStateException if an initial capacity was already set
   */
  public CacheBuilder<K, V> initialCapacity(int initialCapacity) {
    checkState(
        this.initialCapacity == UNSET_INT,
        "initial capacity was already set to %s",
        this.initialCapacity);
    checkArgument(initialCapacity >= 0);
    this.initialCapacity = initialCapacity;
    return this;
  }

  int getInitialCapacity() {
    return (initialCapacity == UNSET_INT) ? DEFAULT_INITIAL_CAPACITY : initialCapacity;
  }

  
Guides the allowed concurrency among update operations. Used as a hint for internal sizing. The
table is internally partitioned to try to permit the indicated number of concurrent updates
without contention. Because assignment of entries to these partitions is not necessarily
uniform, the actual concurrency observed may vary. Ideally, you should choose a value to
accommodate as many threads as will ever concurrently modify the table. Using a significantly
higher value than you need can waste space and time, and a significantly lower value can lead
to thread contention. But overestimates and underestimates within an order of magnitude do not
usually have much noticeable impact. A value of one permits only one thread to modify the cache
at a time, but since read operations and cache loading computations can proceed concurrently,
this still yields higher concurrency than full synchronization.

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.

Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * Guides the allowed concurrency among update operations. Used as a hint for internal sizing. The
   * table is internally partitioned to try to permit the indicated number of concurrent updates
   * without contention. Because assignment of entries to these partitions is not necessarily
   * uniform, the actual concurrency observed may vary. Ideally, you should choose a value to
   * accommodate as many threads as will ever concurrently modify the table. Using a significantly
   * higher value than you need can waste space and time, and a significantly lower value can lead
   * to thread contention. But overestimates and underestimates within an order of magnitude do not
   * usually have much noticeable impact. A value of one permits only one thread to modify the cache
   * at a time, but since read operations and cache loading computations can proceed concurrently,
   * this still yields higher concurrency than full synchronization.
   *
   * <p>Defaults to 4. <b>Note:</b>The default may change in the future. If you care about this
   * value, you should always choose it explicitly.
   *
   * <p>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 {@code concurrencyLevel(1)} in order to achieve more deterministic eviction
   * behavior.
   *
   * <p>Note that future implementations may abandon segment locking in favor of more advanced
   * concurrency controls.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code concurrencyLevel} is nonpositive
   * @throws IllegalStateException if a concurrency level was already set
   */
  public CacheBuilder<K, V> concurrencyLevel(int concurrencyLevel) {
    checkState(
        this.concurrencyLevel == UNSET_INT,
        "concurrency level was already set to %s",
        this.concurrencyLevel);
    checkArgument(concurrencyLevel > 0);
    this.concurrencyLevel = concurrencyLevel;
    return this;
  }

  int getConcurrencyLevel() {
    return (concurrencyLevel == UNSET_INT) ? DEFAULT_CONCURRENCY_LEVEL : concurrencyLevel;
  }

  
Specifies the maximum number of entries the cache may contain.

Note that the cache may evict an entry before this limit is exceeded. For example, in the current implementation, when concurrencyLevel is greater than 1, each resulting segment inside the cache independently limits its own size to approximately maximumSize / concurrencyLevel. 
When eviction is necessary, 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.

If maximumSize is zero, elements will be evicted immediately after being loaded into cache. This can be useful in testing, or to disable caching temporarily. 
This feature cannot be used in conjunction with CacheBuilder<K,V>.maximumWeight. 
Params:
  • maximumSize – the maximum size of the cache
Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * Specifies the maximum number of entries the cache may contain.
   *
   * <p>Note that the cache <b>may evict an entry before this limit is exceeded</b>. For example, in
   * the current implementation, when {@code concurrencyLevel} is greater than {@code 1}, each
   * resulting segment inside the cache <i>independently</i> limits its own size to approximately
   * {@code maximumSize / concurrencyLevel}.
   *
   * <p>When eviction is necessary, 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.
   *
   * <p>If {@code maximumSize} is zero, elements will be evicted immediately after being loaded into
   * cache. This can be useful in testing, or to disable caching temporarily.
   *
   * <p>This feature cannot be used in conjunction with {@link #maximumWeight}.
   *
   * @param maximumSize the maximum size of the cache
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code maximumSize} is negative
   * @throws IllegalStateException if a maximum size or weight was already set
   */
  public CacheBuilder<K, V> maximumSize(long maximumSize) {
    checkState(
        this.maximumSize == UNSET_INT, "maximum size was already set to %s", this.maximumSize);
    checkState(
        this.maximumWeight == UNSET_INT,
        "maximum weight was already set to %s",
        this.maximumWeight);
    checkState(this.weigher == null, "maximum size can not be combined with weigher");
    checkArgument(maximumSize >= 0, "maximum size must not be negative");
    this.maximumSize = maximumSize;
    return this;
  }

  
Specifies the maximum weight of entries the cache may contain. Weight is determined using the Weigher specified with CacheBuilder<K,V>.weigher, and use of this method requires a corresponding call to CacheBuilder<K,V>.weigher prior to calling build. 
Note that the cache may evict an entry before this limit is exceeded. For example, in the current implementation, when concurrencyLevel is greater than 1, each resulting segment inside the cache independently limits its own weight to approximately maximumWeight / concurrencyLevel. 
When eviction is necessary, 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.

If maximumWeight is zero, elements will be evicted immediately after being loaded into cache. This can be useful in testing, or to disable caching temporarily. 
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 CacheBuilder<K,V>.maximumSize. 
Params:
  • maximumWeight – the maximum total weight of entries the cache may contain
Throws:
Returns:this CacheBuilder instance (for chaining)
Since:11.0
/**
   * Specifies the maximum weight of entries the cache may contain. Weight is determined using the
   * {@link Weigher} specified with {@link #weigher}, and use of this method requires a
   * corresponding call to {@link #weigher} prior to calling {@link #build}.
   *
   * <p>Note that the cache <b>may evict an entry before this limit is exceeded</b>. For example, in
   * the current implementation, when {@code concurrencyLevel} is greater than {@code 1}, each
   * resulting segment inside the cache <i>independently</i> limits its own weight to approximately
   * {@code maximumWeight / concurrencyLevel}.
   *
   * <p>When eviction is necessary, 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.
   *
   * <p>If {@code maximumWeight} is zero, elements will be evicted immediately after being loaded
   * into cache. This can be useful in testing, or to disable caching temporarily.
   *
   * <p>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.
   *
   * <p>This feature cannot be used in conjunction with {@link #maximumSize}.
   *
   * @param maximumWeight the maximum total weight of entries the cache may contain
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code maximumWeight} is negative
   * @throws IllegalStateException if a maximum weight or size was already set
   * @since 11.0
   */
  @GwtIncompatible // To be supported
  public CacheBuilder<K, V> maximumWeight(long maximumWeight) {
    checkState(
        this.maximumWeight == UNSET_INT,
        "maximum weight was already set to %s",
        this.maximumWeight);
    checkState(
        this.maximumSize == UNSET_INT, "maximum size was already set to %s", this.maximumSize);
    this.maximumWeight = maximumWeight;
    checkArgument(maximumWeight >= 0, "maximum weight must not be negative");
    return this;
  }

  
Specifies the weigher to use in determining the weight of entries. Entry weight is taken into consideration by maximumWeight(long) when determining which entries to evict, and use of this method requires a corresponding call to maximumWeight(long) prior to calling build. 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.

Params:
  • weigher – the weigher to use in calculating the weight of cache entries
Throws:
Returns:this CacheBuilder instance (for chaining)
Since:11.0
/**
   * Specifies the weigher to use in determining the weight of entries. Entry weight is taken into
   * consideration by {@link #maximumWeight(long)} when determining which entries to evict, and use
   * of this method requires a corresponding call to {@link #maximumWeight(long)} prior to calling
   * {@link #build}. Weights are measured and recorded when entries are inserted into the cache, and
   * are thus effectively static during the lifetime of a cache entry.
   *
   * <p>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).
   *
   * <p><b>Important note:</b> Instead of returning <em>this</em> as a {@code CacheBuilder}
   * instance, this method returns {@code 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 {@code CacheBuilder} type cannot do this. For best results,
   * simply use the standard method-chaining idiom, as illustrated in the documentation at top,
   * configuring a {@code CacheBuilder} and building your {@link Cache} all in a single statement.
   *
   * <p><b>Warning:</b> if you ignore the above advice, and use this {@code CacheBuilder} to build a
   * cache whose key or value type is incompatible with the weigher, you will likely experience a
   * {@link ClassCastException} at some <i>undefined</i> point in the future.
   *
   * @param weigher the weigher to use in calculating the weight of cache entries
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code size} is negative
   * @throws IllegalStateException if a maximum size was already set
   * @since 11.0
   */
  @GwtIncompatible // To be supported
  public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> weigher(
      Weigher<? super K1, ? super V1> weigher) {
    checkState(this.weigher == null);
    if (strictParsing) {
      checkState(
          this.maximumSize == UNSET_INT,
          "weigher can not be combined with maximum size",
          this.maximumSize);
    }

    // safely limiting the kinds of caches this can produce
    @SuppressWarnings("unchecked")
    CacheBuilder<K1, V1> me = (CacheBuilder<K1, V1>) this;
    me.weigher = checkNotNull(weigher);
    return me;
  }

  long getMaximumWeight() {
    if (expireAfterWriteNanos == 0 || expireAfterAccessNanos == 0) {
      return 0;
    }
    return (weigher == null) ? maximumSize : maximumWeight;
  }

  // Make a safe contravariant cast now so we don't have to do it over and over.
  @SuppressWarnings("unchecked")
  <K1 extends K, V1 extends V> Weigher<K1, V1> getWeigher() {
    return (Weigher<K1, V1>) MoreObjects.firstNonNull(weigher, OneWeigher.INSTANCE);
  }

  
Specifies that each key (not value) stored in the cache should be wrapped in a 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. Its Cache.asMap view will therefore technically violate the Map specification (in the same way that IdentityHashMap does). 
Entries with keys that have been garbage collected may be counted in Cache.size, 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. 
Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * Specifies that each key (not value) stored in the cache should be wrapped in a {@link
   * WeakReference} (by default, strong references are used).
   *
   * <p><b>Warning:</b> when this method is used, the resulting cache will use identity ({@code ==})
   * comparison to determine equality of keys. Its {@link Cache#asMap} view will therefore
   * technically violate the {@link Map} specification (in the same way that {@link IdentityHashMap}
   * does).
   *
   * <p>Entries with keys that have been garbage collected may be counted in {@link Cache#size}, 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.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if the key strength was already set
   */
  @GwtIncompatible // java.lang.ref.WeakReference
  public CacheBuilder<K, V> weakKeys() {
    return setKeyStrength(Strength.WEAK);
  }

  CacheBuilder<K, V> setKeyStrength(Strength strength) {
    checkState(keyStrength == null, "Key strength was already set to %s", keyStrength);
    keyStrength = checkNotNull(strength);
    return this;
  }

  Strength getKeyStrength() {
    return MoreObjects.firstNonNull(keyStrength, Strength.STRONG);
  }

  
Specifies that each value (not key) stored in the cache should be wrapped in a 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.size, 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. 
Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * Specifies that each value (not key) stored in the cache should be wrapped in a {@link
   * WeakReference} (by default, strong references are used).
   *
   * <p>Weak values will be garbage collected once they are weakly reachable. This makes them a poor
   * candidate for caching; consider {@link #softValues} instead.
   *
   * <p><b>Note:</b> when this method is used, the resulting cache will use identity ({@code ==})
   * comparison to determine equality of values.
   *
   * <p>Entries with values that have been garbage collected may be counted in {@link Cache#size},
   * 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.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if the value strength was already set
   */
  @GwtIncompatible // java.lang.ref.WeakReference
  public CacheBuilder<K, V> weakValues() {
    return setValueStrength(Strength.WEAK);
  }

  
Specifies that each value (not key) stored in the cache should be wrapped in a 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.size, 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. 
Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * Specifies that each value (not key) stored in the cache should be wrapped in a {@link
   * SoftReference} (by default, strong references are used). Softly-referenced objects will be
   * garbage-collected in a <i>globally</i> least-recently-used manner, in response to memory
   * demand.
   *
   * <p><b>Warning:</b> in most circumstances it is better to set a per-cache {@linkplain
   * #maximumSize(long) 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.
   *
   * <p><b>Note:</b> when this method is used, the resulting cache will use identity ({@code ==})
   * comparison to determine equality of values.
   *
   * <p>Entries with values that have been garbage collected may be counted in {@link Cache#size},
   * 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.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if the value strength was already set
   */
  @GwtIncompatible // java.lang.ref.SoftReference
  public CacheBuilder<K, V> softValues() {
    return setValueStrength(Strength.SOFT);
  }

  CacheBuilder<K, V> setValueStrength(Strength strength) {
    checkState(valueStrength == null, "Value strength was already set to %s", valueStrength);
    valueStrength = checkNotNull(strength);
    return this;
  }

  Strength getValueStrength() {
    return MoreObjects.firstNonNull(valueStrength, Strength.STRONG);
  }

  
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.

When duration is zero, this method hands off to 
maximumSize(0), ignoring any otherwise-specified 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.size, 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. 
Params:
  • duration – the length of time after an entry is created that it should be automatically
    removed
Throws:
Returns:this CacheBuilder instance (for chaining)
Since:25.0
/**
   * 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.
   *
   * <p>When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * <p>Expired entries may be counted in {@link Cache#size}, 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.
   *
   * @param duration the length of time after an entry is created that it should be automatically
   *     removed
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if the time to live or time to idle was already set
   * @throws ArithmeticException for durations greater than +/- approximately 292 years
   * @since 25.0
   */
  @J2ObjCIncompatible
  @GwtIncompatible // java.time.Duration
  public CacheBuilder<K, V> expireAfterWrite(java.time.Duration duration) {
    return expireAfterWrite(duration.toNanos(), TimeUnit.NANOSECONDS);
  }

  
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.

When duration is zero, this method hands off to 
maximumSize(0), ignoring any otherwise-specified 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.size, 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. 
If you can represent the duration as a Duration (which should be preferred when feasible), use expireAfterWrite(Duration) instead. 
Params:
  • duration – the length of time after an entry is created that it should be automatically
    removed
  • unit – the unit that duration is expressed in
Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * 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.
   *
   * <p>When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * <p>Expired entries may be counted in {@link Cache#size}, 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.
   *
   * <p>If you can represent the duration as a {@link java.time.Duration} (which should be preferred
   * when feasible), use {@link #expireAfterWrite(Duration)} instead.
   *
   * @param duration the length of time after an entry is created that it should be automatically
   *     removed
   * @param unit the unit that {@code duration} is expressed in
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if the time to live or time to idle was already set
   */
  public CacheBuilder<K, V> expireAfterWrite(long duration, TimeUnit unit) {
    checkState(
        expireAfterWriteNanos == UNSET_INT,
        "expireAfterWrite was already set to %s ns",
        expireAfterWriteNanos);
    checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
    this.expireAfterWriteNanos = unit.toNanos(duration);
    return this;
  }

  long getExpireAfterWriteNanos() {
    return (expireAfterWriteNanos == UNSET_INT) ? DEFAULT_EXPIRATION_NANOS : expireAfterWriteNanos;
  }

  
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. Access time is reset by all cache read and write operations (including 
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-specified 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.size, 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. 
Params:
  • duration – the length of time after an entry is last accessed that it should be
    automatically removed
Throws:
Returns:this CacheBuilder instance (for chaining)
Since:25.0
/**
   * 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. Access time is reset by all cache read and write operations (including {@code
   * Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by operations on the
   * collection-views of {@link Cache#asMap}.
   *
   * <p>When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * <p>Expired entries may be counted in {@link Cache#size}, 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.
   *
   * @param duration the length of time after an entry is last accessed that it should be
   *     automatically removed
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if the time to idle or time to live was already set
   * @throws ArithmeticException for durations greater than +/- approximately 292 years
   * @since 25.0
   */
  @J2ObjCIncompatible
  @GwtIncompatible // java.time.Duration
  public CacheBuilder<K, V> expireAfterAccess(java.time.Duration duration) {
    return expireAfterAccess(duration.toNanos(), TimeUnit.NANOSECONDS);
  }

  
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. Access time is reset by all cache read and write operations (including 
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-specified 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.size, 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. 
If you can represent the duration as a Duration (which should be preferred when feasible), use expireAfterAccess(Duration) instead. 
Params:
  • 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
Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * 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. Access time is reset by all cache read and write operations (including {@code
   * Cache.asMap().get(Object)} and {@code Cache.asMap().put(K, V)}), but not by operations on the
   * collection-views of {@link Cache#asMap}.
   *
   * <p>When {@code duration} is zero, this method hands off to {@link #maximumSize(long)
   * maximumSize}{@code (0)}, ignoring any otherwise-specified maximum size or weight. This can be
   * useful in testing, or to disable caching temporarily without a code change.
   *
   * <p>Expired entries may be counted in {@link Cache#size}, 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.
   *
   * <p>If you can represent the duration as a {@link java.time.Duration} (which should be preferred
   * when feasible), use {@link #expireAfterAccess(Duration)} instead.
   *
   * @param duration the length of time after an entry is last accessed that it should be
   *     automatically removed
   * @param unit the unit that {@code duration} is expressed in
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if the time to idle or time to live was already set
   */
  public CacheBuilder<K, V> expireAfterAccess(long duration, TimeUnit unit) {
    checkState(
        expireAfterAccessNanos == UNSET_INT,
        "expireAfterAccess was already set to %s ns",
        expireAfterAccessNanos);
    checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
    this.expireAfterAccessNanos = unit.toNanos(duration);
    return this;
  }

  long getExpireAfterAccessNanos() {
    return (expireAfterAccessNanos == UNSET_INT)
        ? DEFAULT_EXPIRATION_NANOS
        : expireAfterAccessNanos;
  }

  
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. The semantics of refreshes are specified in LoadingCache.refresh, and are performed by calling CacheLoader.reload. 
As the default implementation of CacheLoader.reload is synchronous, it is recommended that users of this method override CacheLoader.reload 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.reload 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.

Params:
  • duration – the length of time after an entry is created that it should be considered
    stale, and thus eligible for refresh
Throws:
Returns:this CacheBuilder instance (for chaining)
Since:25.0
/**
   * 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. The semantics
   * of refreshes are specified in {@link LoadingCache#refresh}, and are performed by calling {@link
   * CacheLoader#reload}.
   *
   * <p>As the default implementation of {@link CacheLoader#reload} is synchronous, it is
   * recommended that users of this method override {@link CacheLoader#reload} with an asynchronous
   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *
   * <p>Currently automatic refreshes are performed when the first stale request for an entry
   * occurs. The request triggering refresh will make a blocking call to {@link CacheLoader#reload}
   * and immediately return the new value if the returned future is complete, and the old value
   * otherwise.
   *
   * <p><b>Note:</b> <i>all exceptions thrown during refresh will be logged and then swallowed</i>.
   *
   * @param duration the length of time after an entry is created that it should be considered
   *     stale, and thus eligible for refresh
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if the refresh interval was already set
   * @throws ArithmeticException for durations greater than +/- approximately 292 years
   * @since 25.0
   */
  @J2ObjCIncompatible
  @GwtIncompatible // java.time.Duration
  public CacheBuilder<K, V> refreshAfterWrite(java.time.Duration duration) {
    return refreshAfterWrite(duration.toNanos(), TimeUnit.NANOSECONDS);
  }

  
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. The semantics of refreshes are specified in LoadingCache.refresh, and are performed by calling CacheLoader.reload. 
As the default implementation of CacheLoader.reload is synchronous, it is recommended that users of this method override CacheLoader.reload 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.reload 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.

If you can represent the duration as a Duration (which should be preferred when feasible), use refreshAfterWrite(Duration) instead. 
Params:
  • 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
Throws:
Returns:this CacheBuilder instance (for chaining)
Since:11.0
/**
   * 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. The semantics
   * of refreshes are specified in {@link LoadingCache#refresh}, and are performed by calling {@link
   * CacheLoader#reload}.
   *
   * <p>As the default implementation of {@link CacheLoader#reload} is synchronous, it is
   * recommended that users of this method override {@link CacheLoader#reload} with an asynchronous
   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *
   * <p>Currently automatic refreshes are performed when the first stale request for an entry
   * occurs. The request triggering refresh will make a blocking call to {@link CacheLoader#reload}
   * and immediately return the new value if the returned future is complete, and the old value
   * otherwise.
   *
   * <p><b>Note:</b> <i>all exceptions thrown during refresh will be logged and then swallowed</i>.
   *
   * <p>If you can represent the duration as a {@link java.time.Duration} (which should be preferred
   * when feasible), use {@link #refreshAfterWrite(Duration)} instead.
   *
   * @param duration the length of time after an entry is created that it should be considered
   *     stale, and thus eligible for refresh
   * @param unit the unit that {@code duration} is expressed in
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if the refresh interval was already set
   * @since 11.0
   */
  @GwtIncompatible // To be supported (synchronously).
  public CacheBuilder<K, V> refreshAfterWrite(long duration, TimeUnit unit) {
    checkNotNull(unit);
    checkState(refreshNanos == UNSET_INT, "refresh was already set to %s ns", refreshNanos);
    checkArgument(duration > 0, "duration must be positive: %s %s", duration, unit);
    this.refreshNanos = unit.toNanos(duration);
    return this;
  }

  long getRefreshNanos() {
    return (refreshNanos == UNSET_INT) ? DEFAULT_REFRESH_NANOS : refreshNanos;
  }

  
Specifies a nanosecond-precision time source for this cache. By default, System.nanoTime is used. 
The primary intent of this method is to facilitate testing of caches with a fake or mock
time source.

Throws:
Returns:this CacheBuilder instance (for chaining)
/**
   * Specifies a nanosecond-precision time source for this cache. By default, {@link
   * System#nanoTime} is used.
   *
   * <p>The primary intent of this method is to facilitate testing of caches with a fake or mock
   * time source.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if a ticker was already set
   */
  public CacheBuilder<K, V> ticker(Ticker ticker) {
    checkState(this.ticker == null);
    this.ticker = checkNotNull(ticker);
    return this;
  }

  Ticker getTicker(boolean recordsTime) {
    if (ticker != null) {
      return ticker;
    }
    return recordsTime ? Ticker.systemTicker() : NULL_TICKER;
  }

  
Specifies a listener instance that caches should notify each time an entry is removed for any reason. Each cache created by this builder will invoke this listener as part of the routine maintenance described in the class documentation above. 
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. 
Throws:
Returns:the cache builder reference that should be used instead of this for any remaining configuration and cache building
Returns:this CacheBuilder instance (for chaining)
/**
   * Specifies a listener instance that caches should notify each time an entry is removed for any
   * {@linkplain RemovalCause reason}. Each cache created by this builder will invoke this listener
   * as part of the routine maintenance described in the class documentation above.
   *
   * <p><b>Warning:</b> after invoking this method, do not continue to use <i>this</i> cache builder
   * reference; instead use the reference this method <i>returns</i>. 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 {@link ClassCastException} being thrown
   * by a cache operation at some <i>undefined</i> point in the future.
   *
   * <p><b>Warning:</b> any exception thrown by {@code listener} will <i>not</i> be propagated to
   * the {@code Cache} user, only logged via a {@link Logger}.
   *
   * @return the cache builder reference that should be used instead of {@code this} for any
   *     remaining configuration and cache building
   * @return this {@code CacheBuilder} instance (for chaining)
   * @throws IllegalStateException if a removal listener was already set
   */
  @CheckReturnValue
  public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> removalListener(
      RemovalListener<? super K1, ? super V1> listener) {
    checkState(this.removalListener == null);

    // safely limiting the kinds of caches this can produce
    @SuppressWarnings("unchecked")
    CacheBuilder<K1, V1> me = (CacheBuilder<K1, V1>) this;
    me.removalListener = checkNotNull(listener);
    return me;
  }

  // Make a safe contravariant cast now so we don't have to do it over and over.
  @SuppressWarnings("unchecked")
  <K1 extends K, V1 extends V> RemovalListener<K1, V1> getRemovalListener() {
    return (RemovalListener<K1, V1>)
        MoreObjects.firstNonNull(removalListener, NullListener.INSTANCE);
  }

  
Enable the accumulation of 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. 
Returns:this CacheBuilder instance (for chaining)
Since:12.0 (previously, stats collection was automatic)
/**
   * Enable the accumulation of {@link CacheStats} during the operation of the cache. Without this
   * {@link 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.
   *
   * @return this {@code CacheBuilder} instance (for chaining)
   * @since 12.0 (previously, stats collection was automatic)
   */
  public CacheBuilder<K, V> recordStats() {
    statsCounterSupplier = CACHE_STATS_COUNTER;
    return this;
  }

  boolean isRecordingStats() {
    return statsCounterSupplier == CACHE_STATS_COUNTER;
  }

  Supplier<? extends StatsCounter> getStatsCounterSupplier() {
    return statsCounterSupplier;
  }

  
Builds a cache, which either returns an already-loaded value for a given key or atomically computes or retrieves it using the supplied 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. 
Params:
  • loader – the cache loader used to obtain new values
Returns:a cache having the requested features
/**
   * Builds a cache, which either returns an already-loaded value for a given key or atomically
   * computes or retrieves it using the supplied {@code 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.
   *
   * <p>This method does not alter the state of this {@code CacheBuilder} instance, so it can be
   * invoked again to create multiple independent caches.
   *
   * @param loader the cache loader used to obtain new values
   * @return a cache having the requested features
   */
  public <K1 extends K, V1 extends V> LoadingCache<K1, V1> build(
      CacheLoader<? super K1, V1> loader) {
    checkWeightWithWeigher();
    return new LocalCache.LocalLoadingCache<>(this, loader);
  }

  
Builds a cache which does not automatically load values when keys are requested.

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. 
Returns:a cache having the requested features
Since:11.0
/**
   * Builds a cache which does not automatically load values when keys are requested.
   *
   * <p>Consider {@link #build(CacheLoader)} instead, if it is feasible to implement a {@code
   * CacheLoader}.
   *
   * <p>This method does not alter the state of this {@code CacheBuilder} instance, so it can be
   * invoked again to create multiple independent caches.
   *
   * @return a cache having the requested features
   * @since 11.0
   */
  public <K1 extends K, V1 extends V> Cache<K1, V1> build() {
    checkWeightWithWeigher();
    checkNonLoadingCache();
    return new LocalCache.LocalManualCache<>(this);
  }

  private void checkNonLoadingCache() {
    checkState(refreshNanos == UNSET_INT, "refreshAfterWrite requires a LoadingCache");
  }

  private void checkWeightWithWeigher() {
    if (weigher == null) {
      checkState(maximumWeight == UNSET_INT, "maximumWeight requires weigher");
    } else {
      if (strictParsing) {
        checkState(maximumWeight != UNSET_INT, "weigher requires maximumWeight");
      } else {
        if (maximumWeight == UNSET_INT) {
          logger.log(Level.WARNING, "ignoring weigher specified without maximumWeight");
        }
      }
    }
  }

  
Returns a string representation for this CacheBuilder instance. The exact form of the returned
string is not specified.

/**
   * Returns a string representation for this CacheBuilder instance. The exact form of the returned
   * string is not specified.
   */
  @Override
  public String toString() {
    MoreObjects.ToStringHelper s = MoreObjects.toStringHelper(this);
    if (initialCapacity != UNSET_INT) {
      s.add("initialCapacity", initialCapacity);
    }
    if (concurrencyLevel != UNSET_INT) {
      s.add("concurrencyLevel", concurrencyLevel);
    }
    if (maximumSize != UNSET_INT) {
      s.add("maximumSize", maximumSize);
    }
    if (maximumWeight != UNSET_INT) {
      s.add("maximumWeight", maximumWeight);
    }
    if (expireAfterWriteNanos != UNSET_INT) {
      s.add("expireAfterWrite", expireAfterWriteNanos + "ns");
    }
    if (expireAfterAccessNanos != UNSET_INT) {
      s.add("expireAfterAccess", expireAfterAccessNanos + "ns");
    }
    if (keyStrength != null) {
      s.add("keyStrength", Ascii.toLowerCase(keyStrength.toString()));
    }
    if (valueStrength != null) {
      s.add("valueStrength", Ascii.toLowerCase(valueStrength.toString()));
    }
    if (keyEquivalence != null) {
      s.addValue("keyEquivalence");
    }
    if (valueEquivalence != null) {
      s.addValue("valueEquivalence");
    }
    if (removalListener != null) {
      s.addValue("removalListener");
    }
    return s.toString();
  }
}