public static void printFiles(String path,int level) {
        File f = new File(path);

        String sub = "";
        for (int i =0;i<level-1;i++){
            sub +="  ";
        }

        if(f.isDirectory()) {
            System.err.println(sub+"文件夹: "+f.getName());
            String[] files = f.list();
            for(String filename : files) {
                printFiles(path+"/"+filename,level +1);
            }
        }else {
            System.out.println(sub+"文件： "+f.getName());
        }
    }