Verify uploaded file size

/**
     * 文件校验
     * @param len 长度
     * @param size 大小
     * @param unit 单位
     * @return
     */
    private static void checkFileSize(Long len,int size,String unit){
    
    
        double fileSize = 0;
        if ("B".equalsIgnoreCase(unit)){
    
    
            fileSize = (double)len;
        }else if ("K".equalsIgnoreCase(unit)){
    
    
            fileSize = len>>>10;//
        } else if ("M".equalsIgnoreCase(unit)) {
    
    
            fileSize = len>>>100;
        }else if (("G").equalsIgnoreCase(unit)){
    
    
            fileSize = len>>>1000;
        }
        if (fileSize>size){
    
    
            throw new RestException(1041,"文件大小不能超过"+size+unit);
        }
    }