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* Licensed to the Apache Software Foundation (ASF) under one
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* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
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/*
* Copyright 2010 Google Inc. All Rights Reserved.
*
* 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 org.apache.cayenne.util.concurrentlinkedhashmap;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* A common set of {@link Weigher} implementations.
*
* @author ben.manes@gmail.com (Ben Manes)
* @see <a href="http://code.google.com/p/concurrentlinkedhashmap/">
* http://code.google.com/p/concurrentlinkedhashmap/</a>
*/
final class Weighers {
private Weighers() {
throw new AssertionError();
}
/**
* A weigher where a value has a weight of <tt>1</tt>. A map bounded with this weigher
* will evict when the number of key-value pairs exceeds the capacity.
*
* @return A weigher where a value takes one unit of capacity.
*/
@SuppressWarnings({
"unchecked"
})
public static <V> Weigher<V> singleton() {
return (Weigher<V>) SingletonWeigher.INSTANCE;
}
/**
* A weigher where the value is a byte array and its weight is the number of bytes. A
* map bounded with this weigher will evict when the number of bytes exceeds the
* capacity rather than the number of key-value pairs in the map. This allows for
* restricting the capacity based on the memory-consumption and is primarily for usage
* by dedicated caching servers that hold the serialized data.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value with
* this weight can occur then the caller should eagerly evaluate the value and treat
* it as a removal operation. Alternatively, a custom weigher may be specified on the
* map to assign an empty value a positive weight.
*
* @return A weigher where each byte takes one unit of capacity.
*/
public static Weigher<byte[]> byteArray() {
return ByteArrayWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Iterable} and its weight is the number of
* elements. This weigher only should be used when the alternative
* {@link #collection()} weigher cannot be, as evaluation takes O(n) time. A map
* bounded with this weigher will evict when the total number of elements exceeds the
* capacity rather than the number of key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value with
* this weight can occur then the caller should eagerly evaluate the value and treat
* it as a removal operation. Alternatively, a custom weigher may be specified on the
* map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({
"unchecked"
})
public static <E> Weigher<? super Iterable<E>> iterable() {
return (Weigher<Iterable<E>>) (Weigher<?>) IterableWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Collection} and its weight is the number of
* elements. A map bounded with this weigher will evict when the total number of
* elements exceeds the capacity rather than the number of key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value with
* this weight can occur then the caller should eagerly evaluate the value and treat
* it as a removal operation. Alternatively, a custom weigher may be specified on the
* map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({
"unchecked"
})
public static <E> Weigher<? super Collection<E>> collection() {
return (Weigher<Collection<E>>) (Weigher<?>) CollectionWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link List} and its weight is the number of
* elements. A map bounded with this weigher will evict when the total number of
* elements exceeds the capacity rather than the number of key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value with
* this weight can occur then the caller should eagerly evaluate the value and treat
* it as a removal operation. Alternatively, a custom weigher may be specified on the
* map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({
"unchecked"
})
public static <E> Weigher<? super List<E>> list() {
return (Weigher<List<E>>) (Weigher<?>) ListWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Set} and its weight is the number of
* elements. A map bounded with this weigher will evict when the total number of
* elements exceeds the capacity rather than the number of key-value pairs in the map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value with
* this weight can occur then the caller should eagerly evaluate the value and treat
* it as a removal operation. Alternatively, a custom weigher may be specified on the
* map to assign an empty value a positive weight.
*
* @return A weigher where each element takes one unit of capacity.
*/
@SuppressWarnings({
"unchecked"
})
public static <E> Weigher<? super Set<E>> set() {
return (Weigher<Set<E>>) (Weigher<?>) SetWeigher.INSTANCE;
}
/**
* A weigher where the value is a {@link Map} and its weight is the number of entries.
* A map bounded with this weigher will evict when the total number of entries across
* all values exceeds the capacity rather than the number of key-value pairs in the
* map.
* <p>
* A value with a weight of <tt>0</tt> will be rejected by the map. If a value with
* this weight can occur then the caller should eagerly evaluate the value and treat
* it as a removal operation. Alternatively, a custom weigher may be specified on the
* map to assign an empty value a positive weight.
*
* @return A weigher where each entry takes one unit of capacity.
*/
@SuppressWarnings({
"unchecked"
})
public static <A, B> Weigher<? super Map<A, B>> map() {
return (Weigher<Map<A, B>>) (Weigher<?>) MapWeigher.INSTANCE;
}
private enum SingletonWeigher implements Weigher<Object> {
INSTANCE;
public int weightOf(Object value) {
return 1;
}
}
private enum ByteArrayWeigher implements Weigher<byte[]> {
INSTANCE;
public int weightOf(byte[] value) {
return value.length;
}
}
private enum IterableWeigher implements Weigher<Iterable<?>> {
INSTANCE;
public int weightOf(Iterable<?> values) {
if (values instanceof Collection<?>) {
return ((Collection<?>) values).size();
}
int size = 0;
for (Object value : values) {
size++;
}
return size;
}
}
private enum CollectionWeigher implements Weigher<Collection<?>> {
INSTANCE;
public int weightOf(Collection<?> values) {
return values.size();
}
}
private enum ListWeigher implements Weigher<List<?>> {
INSTANCE;
public int weightOf(List<?> values) {
return values.size();
}
}
private enum SetWeigher implements Weigher<Set<?>> {
INSTANCE;
public int weightOf(Set<?> values) {
return values.size();
}
}
private enum MapWeigher implements Weigher<Map<?, ?>> {
INSTANCE;
public int weightOf(Map<?, ?> values) {
return values.size();
}
}
}