java Timestamp 与字符串的相互转换

1. 概述

本文学习如何将 Java 中的 String 解析为 Timestamp 对象，以及如何将 Timestamp 格式化为字符串。

2. String 转 Timestamp

2.1. 标准时间格式

如何需要解析的时间字符串是JDBC timestamp格式 - yyyy-m[m]-d[d] hh:mm:ss[.f…]，那很简单。使用 Timestamp.valueOf：

Timestamp.valueOf("2018-11-12 01:02:03.123456789")

时间模式说明

Pattern	描述	示例
yyyy	Represents the year, and it’s mandatory to have four digits for it.	2018
m[m]	For the month component, we must have either one or two digits (from 1 to 12).	1, 11
d[d]	For the day of month value, we must have either one or two digits (from 1 to 31).	7, 12
hh	Stands for the hour of the day, with allowed values from 0 to 23.	01, 16
mm	Stands for minutes of the hour, with allowed values from 0 to 59.	02, 45
ss	Stands for seconds in the minute, with allowed values from 0 to 59.	03, 52
[.f…]	Represents optional fractions of a second, can be up to nanoseconds precision so the allowed values are from 0 to 999999999.	12, 1567, 123456789

2.2. 其他时间格式

如果是非 JDBC timestamp 格式的字符串，valueOf 还支持接受 LocalDateTime 类型的参数。

所以我们可以将其转换为LocalDateTime类型，这样我们就支持任意类型的格式了

String pattern = "MMM dd, yyyy HH:mm:ss.SSSSSSSS";
String timestampAsString = "Nov 12, 2018 13:02:56.12345678";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
LocalDateTime localDateTime = LocalDateTime.from(formatter.parse(timestampAsString));

然后调用 Timestamp.valueOf()

Timestamp timestamp = Timestamp.valueOf(localDateTime);
assertEquals("2018-11-12 13:02:56.12345678", timestamp.toString());

3. Timestamp 转 String

同样，默认格式输出的是 JDBC timestamp类型

assertEquals("2018-11-12 13:02:56.12345678", timestamp.toString());

通过中间类转换为 ISO-8601 标准格式：

Timestamp timestamp = Timestamp.valueOf("2018-12-12 01:02:03.123456789");
DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
 
String timestampAsString = formatter.format(timestamp.toLocalDateTime());
assertEquals("2018-12-12T01:02:03.123456789", timestampAsString);

4. 总结

本文中的示例源码可在GitHub上获取。