android开发常用的缓存策略详解（3）- 缓存中的时间超过我们设定的值，将其删除

这个小编就不做过多的讲解了，还是以Universal-Image-Loader 中的LimitedAgeMemoryCache 为例进行代码的分析

提供缓存的特殊功能：如果某些缓存对象的时间超过定义值，则该对象将从缓存中删除

public class LimitedAgeMemoryCache<K, V> implements MemoryCacheAware<K, V> {

    private final MemoryCacheAware<K, V> cache;

    private final long maxAge;
    private final Map<K, Long> loadingDates = Collections.synchronizedMap(new HashMap<K, Long>());

    /**
     * @param cache  Wrapped memory cache
     * @param maxAge Max object age <b>(in seconds)</b>. If object age will exceed this value then it'll be removed from
     *               cache on next treatment (and therefore be reloaded).
     */
    public LimitedAgeMemoryCache(MemoryCacheAware<K, V> cache, long maxAge) {
        this.cache = cache;
        this.maxAge = maxAge * 1000; // to milliseconds
    }

    @Override
    public boolean put(K key, V value) {
        boolean putSuccesfully = cache.put(key, value);
        if (putSuccesfully) {
            loadingDates.put(key, System.currentTimeMillis());
        }
        return putSuccesfully;
    }


    @Override
    public V get(K key) {
        Long loadingDate = loadingDates.get(key);
        if (loadingDate != null && System.currentTimeMillis() - loadingDate > maxAge) {
            cache.remove(key);   
            loadingDates.remove(key);
        }//判断如果超过了预设的时间进行响应的删除

        return cache.get(key);
    }

    @Override
    public void remove(K key) {
        cache.remove(key);
        loadingDates.remove(key);
    }

    @Override
    public Collection<K> keys() {
        return cache.keys();
    }

    @Override
    public void clear() {
        cache.clear();
        loadingDates.clear();
    }