JAVA计算文件大小

File f = new File(save_path+File.separator + resouce_id+".zip");
        FileInputStream fis = new FileInputStream(f);
        
        String resource_size = "";

        DecimalFormat df = new DecimalFormat("#.##");
        
        double resourcesize = (double)((double)fis.available()/1024);
        
        if((double)((double)fis.available()/1024)>1000)
        {
            resource_size =df.format((double)((double)fis.available()/1024/1024))+"MB";
        }
        else
        {
            resource_size =df.format((double)((double)fis.available()/1024))+"KB";
        }