import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 public class Cache {
     private final ConcurrentHashMap<Object,CacheNode> map;
     private final long timeOut;
     private ScheduledExecutorService thread;
     //无参构造永久不过期
     public Cache(){
         this(0);
     }
     //有参构造设置过期时间
     public Cache(long timeOut){
         map = new ConcurrentHashMap<>();
         this.timeOut = timeOut;
         //定时清理过期数据
         thread = Executors.newSingleThreadScheduledExecutor();
         thread.scheduleAtFixedRate(this::clearTimeOut,2,2,TimeUnit.SECONDS);
     }
     //存入缓存
     public void put(Object key,Object value){
         put(key,value,timeOut);
     }
     //自定义过期时间存放
     public void put(Object key,Object value,long ttl){
         long endTime = ttl == 0 ? Long.MAX_VALUE : System.currentTimeMillis()+ttl;
         map.put(key,new CacheNode(value,endTime));
     }
     //获取缓存
     public Object get(Object key){
         CacheNode node = map.get(key);
         if(node == null){
             return null;
         }
         //判断是否过期
         if(System.currentTimeMillis()>node.endTime){
             map.remove(key);
             return null;
         }
         return node.value;
     }
     //删除缓存
     public void remove(Object key){
         map.remove(key);
     }
     //清理过期数据
     private void clearTimeOut(){
         map.entrySet().removeIf(e->System.currentTimeMillis()>e.getValue().endTime);
     }
     //关闭线程防止资源泄露
     public void close(){
         thread.shutdown();
     }
     //内部存储节点
     private static class CacheNode{
         Object value;
         long endTime;
         public CacheNode(Object value,long endTime){
             this.value = value;
             this.endTime = endTime;
         }
     }
     //测试运行
     public static void main(String[] args) throws InterruptedException {
         //设置5秒过期
         Cache cache = new Cache(5000);
         cache.put("学号","2026001");
         System.out.println("存入立刻获取："+cache.get("学号"));
         Thread.sleep(6000);
         System.out.println("6秒后获取（已过期）："+cache.get("学号"));
         cache.close();
     }
 }