SimpleDateFormat 格式化到毫秒

在开发时，某些场景是需要格式化时间到毫秒等精度，比如生成文件名字等，实现代码如下：

    SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmssSSS");
    System.out.println("======"+sdf.format(new Date()));
    SimpleDateFormat sdf1 = new SimpleDateFormat("yyyyMMddHHmmssSSSXXX");
    System.out.println("======"+sdf1.format(new Date()));
    SimpleDateFormat sdf11 = new SimpleDateFormat("yyyyMMddHHmmssSSSSSSSSS");
    System.out.println("======"+sdf11.format(new Date()));
    SimpleDateFormat sdf111 = new SimpleDateFormat("yyyyMMddHHmmssSSSSSSSSSXXX");
    System.out.println("======"+sdf111.format(new Date()));
    System.out.println("======"+System.currentTimeMillis());


输出结果：
======20200404011237062
======20200404011237063+08:00
======20200404011237000000063
======20200404011237000000064+08:00
======1585933957064