Java 日期转字符串

public void convertstrtotime() {
String aString = "2017-11-12 23:46:30";
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
long aTime = 0L;
try {
aTime = format.parse(aString).getTime();
} catch (ParseException e) {
e.printStackTrace();
}

System.out.println(aTime);

SimpleDateFormat aDate1 = new SimpleDateFormat("yyyy-MM-dd");
System.out.println("日期:" + aDate1.format(aTime));

SimpleDateFormat aDate2 = new SimpleDateFormat("yyyy-MM-dd HH:mm");
System.out.println("日期时分:" + aDate2.format(aTime));

SimpleDateFormat aDate3 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println("日期时分秒:" + aDate3.format(aTime));

}

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1510501590000
日期:2017-11-12
日期时分:2017-11-12 23:46
日期时分秒:2017-11-12 23:46:30