java手写本地缓存示例

package com.negen; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.stream.Collectors; /** * @author Negen * @date 2022年7月28日20:25:47 * @description 缓存工具类 */ public class CacheUtil { /** * 存储键值对 */ private ConcurrentHashMap<String, Object> cacheMap = null; /** * 存储键值对的有效时间 */ private ConcurrentHashMap<String, Long> expireMap = null; /** * 默认过期时间(毫秒 ) */ private final long DEFAULT_EXPIRE_TIME = 1000 * 3600 * 24 * 30; private static CacheUtil instance = null; public static CacheUtil getInstance(){ if (null == instance){ synchronized (CacheUtil.class){ if (null == instance)instance = new CacheUtil(); } } return instance; } CacheUtil(){ cacheMap = new ConcurrentHashMap<>(); expireMap = new ConcurrentHashMap<>(); } /** * 添加键值对 默认失效时间30天 * @param key * @param value */ public void put(String key, Object value){ this.put(key, value, DEFAULT_EXPIRE_TIME); } /** * 添加键值对 自定义失效时间（毫秒） * @param key * @param value * @param expire 有效期 */ public void put(String key, Object value, long expire){ cacheMap.put(key, value); expireMap.put(key, System.currentTimeMillis() + expire); } /** * 根据 key 获取相应的 value * @param key * @return */ public Object get(String key){ return cacheMap.get(key); } /** * 删除键值对 * @param key * @return 被删除的键值对个数 */ public int remove(String key){ int beforeRemoveCount = cacheMap.size(); cacheMap.remove(key); expireMap.remove(key); int afterRemoveCount = cacheMap.size(); return beforeRemoveCount - afterRemoveCount; } /** * 处理已经过期的键值对 * @return */ public int handleExpireKeys(){ long now = System.currentTimeMillis(); int beforeRemoveCount = cacheMap.size(); List<Map.Entry<String, Long>> collect = expireMap.entrySet().stream() .sorted((entry1, entry2) -> entry1.getValue().compareTo(entry2.getValue())) .collect(Collectors.toList()); Iterator<Map.Entry<String, Long>> iterator = collect.iterator(); while (iterator.hasNext()){ Map.Entry<String, Long> kv = iterator.next(); String key = kv.getKey(); Long expireTime = kv.getValue(); if (expireTime < now){ this.remove(key); System.out.println(String.format("%s过期，已删除", key)); } } int afterRemoveCount = cacheMap.size(); int removeCount = beforeRemoveCount - afterRemoveCount; if (removeCount < 0)removeCount = 0; System.out.println("当前过期键值对：" + removeCount); return removeCount; } }