要使用dateTimeFormatter将LocalDateTime类型转换为String类型：dateTimeFormatter.format(currentTime)

代码如下：
public static void getDay(){
    DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    LocalDateTime currentTime = LocalDateTime.now();
    LocalDateTime parse = LocalDateTime.parse( dateTimeFormatter.format(currentTime),dateTimeFormatter);
    //当前时间的毫秒数
    long times = LocalDateTime.from(parse).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
    System.out.println("times = " + times);
}