一、前言

通过googlecode源码concurrentlinkedhashmap-lru-1.4.2.jar包中的com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap定义GoogleConcurrentLruCache类实现LRU cache缓存策略,详情代码示例部分。

二、代码示例

import java.util.Set;@b@import java.util.concurrent.atomic.AtomicLong;@b@@b@import com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap;@b@import com.googlecode.concurrentlinkedhashmap.EvictionListener;@b@import com.googlecode.concurrentlinkedhashmap.Weighers;@b@@b@/**@b@ * 基于google concurrent的LinkedHashMap实现LRU  @b@ */@b@public class GoogleConcurrentLruCache<K, V> {@b@@b@    private ConcurrentLinkedHashMap<K, V> cache;@b@    private static final int              DEFAULT_CAPACITY         = 389;@b@    public static final int               DEFAULT_CONCURENCY_LEVEL = 64;@b@    private AtomicLong                    get                      = new AtomicLong(0);@b@    private AtomicLong                    hit                      = new AtomicLong(0);@b@@b@    public GoogleConcurrentLruCache(){@b@        this(DEFAULT_CAPACITY);@b@    }@b@@b@    public GoogleConcurrentLruCache(int capacity){@b@        if (capacity <= 0) {@b@            capacity = DEFAULT_CAPACITY;@b@        }@b@@b@        cache = new ConcurrentLinkedHashMap.Builder<K, V>().maximumWeightedCapacity(capacity)@b@            .weigher(Weighers.singleton())@b@            .concurrencyLevel(DEFAULT_CONCURENCY_LEVEL)@b@            .build();@b@    }@b@@b@    public GoogleConcurrentLruCache(int capacity, EvictionListener<K, V> listener){@b@        if (capacity <= 0) {@b@            capacity = DEFAULT_CAPACITY;@b@        }@b@@b@        cache = new ConcurrentLinkedHashMap.Builder<K, V>().maximumWeightedCapacity(capacity)@b@            .weigher(Weighers.singleton())@b@            .concurrencyLevel(DEFAULT_CONCURENCY_LEVEL)@b@            .listener(listener)@b@            .build();@b@    }@b@@b@    public long capacity() {@b@        return cache.capacity();@b@    }@b@@b@    public boolean isEmpty() {@b@        return cache.isEmpty();@b@    }@b@@b@    public int size() {@b@        return cache.size();@b@    }@b@@b@    public void clear() {@b@        cache.clear();@b@    }@b@@b@    public V get(Object key) {@b@        V v = cache.get(key);@b@        get.addAndGet(1);@b@        if (v != null) {@b@            hit.addAndGet(1);@b@        }@b@@b@        return v;@b@    }@b@@b@    public void put(K key, V value) {@b@        cache.put(key, value);@b@    }@b@@b@    public boolean putIfAbsent(K key, V value) {@b@        return cache.putIfAbsent(key, value) == null;@b@    }@b@@b@    public boolean replace(K key, V old, V value) {@b@        return cache.replace(key, old, value);@b@    }@b@@b@    public void remove(K key) {@b@        cache.remove(key);@b@    }@b@@b@    public Set<K> keySet() {@b@        return cache.keySet();@b@    }@b@@b@    public Set<K> hotKeySet(int n) {@b@        return cache.descendingKeySetWithLimit(n);@b@    }@b@@b@    public boolean containsKey(K key) {@b@        return cache.containsKey(key);@b@    }@b@@b@    public String getStatus() {@b@        StringBuilder sb = new StringBuilder();@b@        sb.append("current size:");@b@        sb.append(cache.size());@b@        sb.append(" get:");@b@        sb.append(get);@b@        sb.append(" hit:");@b@        sb.append(hit);@b@        sb.append(" hit ratio:");@b@        if (get.longValue() > 0) {@b@            sb.append((hit.doubleValue() / get.doubleValue()) * 100);@b@            sb.append("%");@b@        } else {@b@            sb.append("--");@b@        }@b@@b@        get.set(0);@b@        hit.set(0);@b@@b@        return sb.toString();@b@    }@b@}