文件过滤器

    /**     * A filename filter to use to identify the cache filenames which have CACHE_FILENAME_PREFIX     * prepended.     */    private static final FilenameFilter cacheFileFilter = new FilenameFilter() {        @Override        public boolean accept(File dir, String filename) {            return filename.startsWith(CACHE_FILENAME_PREFIX);        }    };

获取文件夹下 ，以特定字符串开头的文件。