public Scanner(String rootDir, int interval) {
		if (StrKit.isBlank(rootDir)) {
			throw new IllegalArgumentException("the rootDir can not be blank");
		}
		this.rootDir = new File(rootDir);
		if (!this.rootDir.isDirectory()) {
			throw new IllegalArgumentException("the "+rootDir+"is not a directory");
		}
		if (interval < 0) {
			throw new IllegalArgumentException("interval must bigger than zear");
		}
		this.interval = interval;
	}