8.16 lru缓存java版

本文主要是介绍8.16 lru缓存java版，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

lru详细介绍及简单代码实现:
http://blog.csdn.net/beiyetengqing/article/details/7855933

以下是本人的加强的lru缓存类，增加单例获取、缓存超时机制和修复一个clear()的bug

package com.george.xblog.utils;import java.util.Hashtable;
import java.util.Map;/*** Created by george.yang on 15/8/15.*/
public class LruCache {private static final class Entry {public String key;// 键public Object value;// 值public Entry prev;// 前一节点public Entry next;// 后一节点public long validTime;//有效的最大时间}private static LruCache instance;public static synchronized LruCache getInstance() {if (instance==null) {instance = new LruCache(100);}return instance;}private int cacheSize;private Map<String, Entry> nodes;// 缓存容器private Entry first;// 链表头private Entry last;// 链表尾public LruCache(int i) {cacheSize = i;nodes = new Hashtable<String, Entry>(i);//缓存容器}/*** 获取缓存中对象,并把它放在最前面*/public <T> T get(String key) {Entry node = nodes.get(key);if (node != null) {if (System.currentTimeMillis()>node.validTime) {//在链表中删除remove(node);//在hashtable中删除nodes.remove(key);} else {moveToHead(node);return (T)node.value;}}return null;}/*** 加入缓存* 添加 entry到hashtable, 并把entry* @param key* @param timeout 超时时间，毫秒* @param value*/public void put(String key,long timeout, Object value) {//先查看hashtable是否存在该entry, 如果存在，则只更新其valueEntry node = nodes.get(key);if (node == null) {//缓存容器是否已经超过大小.if (nodes.size() >= cacheSize) {nodes.remove(last.key);removeLast();}node = new Entry();}node.validTime = System.currentTimeMillis() + timeout;node.value = value;//将最新使用的节点放到链表头，表示最新使用的.moveToHead(node);nodes.put(key, node);}/*** 将entry删除, 注意：删除操作只有在cache满了才会被执行*/public void remove(String key) {Entry node = nodes.get(key);//在链表中删除remove(node);//在hashtable中删除nodes.remove(key);}private void remove(Entry node) {if (node != null) {if (node.prev != null) {node.prev.next = node.next;}if (node.next != null) {node.next.prev = node.prev;}if (last == node)last = node.prev;if (first == node)first = node.next;}}/*** 删除链表尾部节点，即使用最后 使用的entry*/private void removeLast() {//链表尾不为空,则将链表尾指向null. 删除连表尾（删除最少使用的缓存对象）if (last != null) {if (last.prev != null)last.prev.next = null;elsefirst = null;last = last.prev;}}/*** 移动到链表头，表示这个节点是最新使用过的*/private void moveToHead(Entry node) {if (node == first)return;if (node.prev != null)node.prev.next = node.next;if (node.next != null)node.next.prev = node.prev;if (last == node)last = node.prev;if (first != null) {node.next = first;first.prev = node;}first = node;node.prev = null;if (last == null)last = first;}/** 清空缓存*/public void clear() {first = null;last = null;nodes = new Hashtable<String, Entry>(cacheSize);}
}

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