java代码实现LRU淘汰策略

LRU: Least Recently Used,最近最少使用的淘汰策略;

在redis中最常使用作为数据淘汰策略;

1. 代码实现

package com.test.wei.biz.lru;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * 使用双向链表实现LRU过期数据淘汰策略
 *
 * @author zhangshiwei
 * @since 2020年11月27日 下午5:29:18
 */
public class LruTest {

    public static void main(String[] args) {
        LruCache lruCache = new LruCache(5);
        lruCache.set("A", "1");
        lruCache.set("B", "2");
        lruCache.set("C", "3");
        lruCache.set("D", "4");
        List<Object> allList = new ArrayList<>();
        allList = lruCache.getAll(lruCache.head, allList);
        System.out.println("新增后 - allList: " + allList);

        lruCache.set("E", "5");
        allList = new ArrayList<>();
        allList = lruCache.getAll(lruCache.head, allList);
        System.out.println("新增后 - allList: " + allList);

        lruCache.set("F", "6");
        allList = new ArrayList<>();
        allList = lruCache.getAll(lruCache.head, allList);
        System.out.println("新增后 - allList: " + allList);

        lruCache.set("G", "7");
        allList = new ArrayList<>();
        allList = lruCache.getAll(lruCache.head, allList);
        System.out.println("新增后 - allList: " + allList);

        LruNode fNode = lruCache.get("F");
        System.out.println("从lruCache中读取: " + fNode.key + " - " + fNode.value);
        allList = new ArrayList<>();
        allList = lruCache.getAll(lruCache.head, allList);
        System.out.println("读取后 - allList: " + allList);
    }

    public static class LruNode {
        String  key;
        Object  value;
        LruNode pre;
        LruNode next;

        public LruNode(String key, Object value) {
            this.key = key;
            this.value = value;
        }
    }

    public static class LruCache {
        // 用KV形式存储对象(内部对象维护双向链表), 链表容量, 头结点, 尾节点
        private HashMap<String, LruNode> map;
        private int                      capacity;
        private LruNode                  head;
        private LruNode                  tail;

        public LruCache(int capacity) {
            this.capacity = capacity;
            this.map = new HashMap<>(capacity);
        }

        public void set(String key, Object value) {
            System.out.println("新增节点的value:" + value);

            LruNode node = map.get(key);
            if (node != null) {
                node.value = value;
                remove(node, false);
            } else {
                node = new LruNode(key, value);

                if (map.size() >= capacity) {
                    System.out.println("空间不足,删除尾节点: " + tail.value);
                    remove(tail, true);
                }
                map.put(key, node);
            }

            // 新增的元素放在队首
            setHead(node);
        }

        // 移除节点
        private void remove(LruNode node, boolean flag) {
            if (null != node.pre) {
                node.pre.next = node.next;
            } else {
                head = node.next;
            }
            if (null != node.next) {
                node.next.pre = node.pre;
            } else {
                tail = node.pre;
            }

            node.pre = null;
            node.next = null;

            if (flag) {
                map.remove(node.key);
            }
        }

        // 设置头节点
        private void setHead(LruNode node) {
            if (null != head) {
                node.next = head;
                head.pre = node;
            }
            head = node;
            if (null == tail) {
                tail = node;
            }
        }

        // 根据key获取节点值,并将此节点移动到队首
        public LruNode get(String key) {
            LruNode node = map.get(key);
            if (null != node) {
                remove(node, false);
                setHead(node);
                return node;
            }
            return null;
        }

        // 获取所有元素的value值
        public List<Object> getAll(LruNode node, List<Object> allList) {
            if (null != node) {
                allList.add(node.value);
                if (null != node.next) {
                    this.getAll(node.next, allList);
                }
            }
            return allList;
        }

    }

}

2. 测试结果

 

本文地址：https://blog.csdn.net/weixin_41564440/article/details/110240796