How to get the current time in YYYY-MM-DD HH:MI:Sec.Millisecond format in Java?

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");

A Java one liner

public String getCurrentTimeStamp() {
    return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date());
}

in JDK8 style

public String getCurrentLocalDateTimeStamp() {
    return LocalDateTime.now()
       .format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS"));
}

You only have to add the millisecond field in your date format string:

new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");

The API doc of SimpleDateFormat describes the format string in detail.