android缓存机制

一般android会采用缓存机制，内存缓存采用LruCache，存储缓存采用DiskLruCache
LruCache内部维护了一个LinkedHashMap

 /**
     * @param maxSize for caches that do not override {@link #sizeOf}, this is
     *     the maximum number of entries in the cache. For all other caches,
     *     this is the maximum sum of the sizes of the entries in this cache.
     */
    public LruCache(int maxSize) {
        if (maxSize <= 0) {
            throw new IllegalArgumentException("maxSize <= 0");
        }
        this.maxSize = maxSize;
        this.map = new LinkedHashMap(0, 0.75f, true);
    }

同时是线程安全的

   synchronized (this) {
            mapValue = map.get(key);
            if (mapValue != null) {
                hitCount++;
                return mapValue;
            }
            missCount++;
        }
   synchronized (this) {
            createCount++;
            mapValue = map.put(key, createdValue);

            if (mapValue != null) {
                // There was a conflict so undo that last put
                map.put(key, mapValue);
            } else {
                size += safeSizeOf(key, createdValue);
            }
        }

一般存储空间为当前运行空间的1／8 单位为KB
LruCache 3.1以后源码可见
DiskLruCache 一般存储空间为50M key采用url经过Md5加密，防止url中的特殊字符，value为bitmap，对外提供get，put方法