一个负责存储短暂对象的Map，定时清理过期的对象

刺骨的言语ヽ痛彻心扉 2021-10-24 00:50 219阅读 0赞

>     import java.util.*;
>     
>     /**
>      * 用来存储短暂对象的缓存类，实现Map接口，内部有一个定时器用来清除过期（3600000秒既1小时）的对象。
>      * 为避免创建过多线程，没有特殊要求请使用getDefault()方法来获取本类的实例。
>      *
>      * @param <K>
>      * @param <V>
>      */
>     
>     public class CacheMap<K, V> extends AbstractMap<K, V> {
>     
>         private static final long DEFAULT_TIMEOUT = 3600000;
>         private static CacheMap<Object, Object> defaultInstance;
>     
>         public static synchronized final CacheMap<Object, Object> getDefault() {
>             if (defaultInstance == null) {
>                 defaultInstance = new CacheMap<Object, Object>(DEFAULT_TIMEOUT);
>             }
>             return defaultInstance;
>         }
>     
>         private class CacheEntry implements Entry<K, V> {
>             long time;
>             V value;
>             K key;
>     
>             CacheEntry(K key, V value) {
>                 super();
>                 this.value = value;
>                 this.key = key;
>                 this.time = System.currentTimeMillis();
>             }
>     
>             @Override
>             public K getKey() {
>                 return key;
>             }
>     
>             @Override
>             public V getValue() {
>                 return value;
>             }
>     
>             @Override
>             public V setValue(V value) {
>                 return this.value = value;
>             }
>         }
>     
>         private class ClearThread extends Thread {
>             ClearThread() {
>                 setName("clear cache thread");
>             }
>     
>             public void run() {
>                 while (true) {
>                     try {
>                         long now = System.currentTimeMillis();
>                         Object[] keys = map.keySet().toArray();
>                         for (Object key : keys) {
>                             CacheEntry entry = map.get(key);
>                             if (now - entry.time >= cacheTimeout) {
>                                 synchronized (map) {
>                                     map.remove(key);
>                                 }
>                             }
>                         }
>                         Thread.sleep(cacheTimeout);
>                     } catch (Exception e) {
>                         e.printStackTrace();
>                     }
>                 }
>             }
>         }
>     
>         private long cacheTimeout;
>         private Map<K, CacheEntry> map = new HashMap<K, CacheEntry>();
>     
>         public CacheMap(long timeout) {
>             this.cacheTimeout = timeout;
>             new ClearThread().start();
>         }
>     
>         @Override
>         public Set<Entry<K, V>> entrySet() {
>             Set<Entry<K, V>> entrySet = new HashSet<Entry<K, V>>();
>             Set<Entry<K, CacheEntry>> wrapEntrySet = map.entrySet();
>             for (Entry<K, CacheEntry> entry : wrapEntrySet) {
>                 entrySet.add(entry.getValue());
>             }
>             return entrySet;
>         }
>     
>         @Override
>         public V get(Object key) {
>             CacheEntry entry = map.get(key);
>             return entry == null ? null : entry.value;
>         }
>     
>         @Override
>         public V put(K key, V value) {
>             CacheEntry entry = new CacheEntry(key, value);
>             synchronized (map) {
>                 map.put(key, entry);
>             }
>             return value;
>         }
>     
>     }