Table of Contents

LocalDateTime in Java with Examples

區分了時間戳、本地日期、本地時間和帶時區的日期時間，LocalDateTime in Java 介紹常見的 format 、 parse 、 ofInstant 等方法，本篇增加了範例，並透過單元測試來驗證產出結果。

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- datetime
       |                   +- localdatetime
       |                       +- LocalDateTimeWithExamplesTest.java

單元測試

LocalDateTime Java 提供日期時間建立、格式化等操作 LocalDateTime 。

format

建立一個 LocalDateTime ，格式化指定日期時間。

	@Test
	public void format() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3);
		String result = localDateTime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result);

		localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		result = localDateTime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03.123456789", result);

		result = localDateTime.format(DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss.SSS"));
		System.out.println(result);
		assertEquals("2023/08/03 01:02:03.123", result);
	}

2023-08-03T01:02:03
2023-08-03T01:02:03.123456789
2023/08/03 01:02:03.123

parse

LocalDateTime Java 建立一個 LocalDateTime ，使用 String 建立指定日期時間。

	@Test
	public void parse() {
		LocalDateTime localDateTime = LocalDateTime.parse("2023-08-03T01:02:03");
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());
		
		localDateTime = LocalDateTime.parse("2023-08-03T01:02:03.123456789");
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123456789", localDateTime.toString());

		localDateTime = LocalDateTime.parse("2023/08/03 01:02:03.123", DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss.SSS"));
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123", localDateTime.toString());
	}

2023-08-03T01:02:03
2023-08-03T01:02:03.123456789
2023-08-03T01:02:03.123

from

LocalDateTime Java 建立一個 LocalDateTime ，從另一個日期時間，建立指定日期時間。

	@Test
	public void from() {
		LocalDateTime localDateTime = LocalDateTime.parse("2023-08-03T01:02:03");
		LocalDateTime result = LocalDateTime.from(localDateTime);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result.toString());
		
		localDateTime = LocalDateTime.parse("2023-08-03T01:02:03");
		ZoneOffset zoneOffset = ZoneOffset.of("+09:00");
		OffsetDateTime offsetDateTime = OffsetDateTime.of(localDateTime, zoneOffset);
		System.out.println(offsetDateTime);
		result = LocalDateTime.from(offsetDateTime);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result.toString());

		ZonedDateTime zonedDateTime = ZonedDateTime.parse("2023-08-03T01:02:03+09:00[Asia/Tokyo]");
		result = LocalDateTime.from(zonedDateTime);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result.toString());
	}

2023-08-03T01:02:03
2023-08-03T01:02:03+09:00
2023-08-03T01:02:03
2023-08-03T01:02:03

ofInstant

LocalDateTime Java 建立一個 LocalDateTime ，使用 Instant 建立指定日期時間。

	@Test
	public void ofInstant() {
		ZoneId zone = ZoneId.of("UTC+9");
		Instant instant = Instant.ofEpochSecond(1690992123L);
		LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		instant = Instant.ofEpochSecond(1690992123L, 123456789);
		localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123456789", localDateTime.toString());
	}

2023-08-03T01:02:03
2023-08-03T01:02:03.123456789

toEpochSecond

Java LocalDateTime 建立一個 LocalDateTime ，取得紀元秒，從 UTC 的 1970-01-01T00:00:00Z 起。

	@Test
	public void toEpochSecond() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3);
		ZoneOffset zoneOffset = ZoneOffset.of("+09:00");
		long result = localDateTime.toEpochSecond(zoneOffset);
		System.out.println(result);
		assertEquals(1690992123L, result);

		localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		zoneOffset = ZoneOffset.of("+09:00");
		result = localDateTime.toEpochSecond(zoneOffset);
		System.out.println(result);
		assertEquals(1690992123L, result);
	}

1690992123
1690992123

toEpochMilli

Java LocalDateTime 建立一個 LocalDateTime ，取得紀元毫秒，從 UTC 的 1970-01-01T00:00:00Z 起。

	@Test
	public void toEpochMilli() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3);
		ZoneId zone = ZoneId.of("UTC+9");
		Instant instant = localDateTime.atZone(zone).toInstant();
		long result = instant.toEpochMilli();
		System.out.println(result);
		assertEquals(1690992123000L, result);

		localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		zone = ZoneId.of("UTC+9");
		instant = localDateTime.atZone(zone).toInstant();
		result = instant.toEpochMilli();
		System.out.println(result);
		assertEquals(1690992123123L, result);
	}

1690992123000
1690992123123

ofEpochSecond

Java LocalDateTime 建立一個 LocalDateTime ，將紀元秒轉成指定日期時間。

	@Test
	public void ofEpochSecond() {
		ZoneOffset zoneOffset = ZoneOffset.of("+09:00");
		LocalDateTime localDateTime = LocalDateTime.ofEpochSecond(1690992123L, 0, zoneOffset);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		localDateTime = LocalDateTime.ofEpochSecond(1690992123L, 123456789, zoneOffset);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123456789", localDateTime.toString());
	}

2023-08-03T01:02:03
2023-08-03T01:02:03.123456789

ofEpochMilli

Java LocalDateTime 建立一個 LocalDateTime ，將紀元毫秒轉成指定日期時間

	@Test
	public void ofEpochMilli() {
		ZoneId zone = ZoneId.of("UTC+9");
		Instant instant = Instant.ofEpochMilli(1690992123000L);
		LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		instant = Instant.ofEpochMilli(1690992123123L);
		localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123", localDateTime.toString());
	}

2023-08-03T01:02:03
2023-08-03T01:02:03.123

timestamp

Java LocalDateTime 建立一個 LocalDateTime ，使用 Timestamp 建立指定日期時間。

	@Test
	public void timestamp() {
		LocalDateTime localDateTime = new Timestamp(1690995723000L).toLocalDateTime();
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		localDateTime = new Timestamp(1690995723123L).toLocalDateTime();
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123", localDateTime.toString());
	}

2023-08-03T01:02:03
2023-08-03T01:02:03.123

truncatedTo

Java LocalDateTime 建立一個 LocalDateTime ，捨棄欄位到指定欄位。

	@Test
	public void truncatedTo() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		LocalDateTime result = localDateTime.truncatedTo(ChronoUnit.HOURS);
		System.out.println(result);
		assertEquals("2023-08-03T01:00", result.toString());

		result = localDateTime.truncatedTo(ChronoUnit.DAYS);
		System.out.println(result);
		assertEquals("2023-08-03T00:00", result.toString());
		
		result = localDateTime.truncatedTo(ChronoUnit.MILLIS);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03.123", result.toString());
	}

2023-08-03T01:00
2023-08-03T00:00
2023-08-03T01:02:03.123

LocalDateTimeWithExamplesTest.java

LocalDateTime in Java 新增單元測試，驗證 Java LocalDateTime Example 是否符合預期。

package org.ruoxue.java_147.datetime.localdatetime;

import static org.junit.Assert.*;

import java.sql.Timestamp;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;

import org.junit.Test;

public class LocalDateTimeWithExamplesTest {

	@Test
	public void format() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3);
		String result = localDateTime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result);

		localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		result = localDateTime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03.123456789", result);

		result = localDateTime.format(DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss.SSS"));
		System.out.println(result);
		assertEquals("2023/08/03 01:02:03.123", result);
	}

	@Test
	public void parse() {
		LocalDateTime localDateTime = LocalDateTime.parse("2023-08-03T01:02:03");
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		localDateTime = LocalDateTime.parse("2023-08-03T01:02:03.123456789");
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123456789", localDateTime.toString());

		localDateTime = LocalDateTime.parse("2023/08/03 01:02:03.123",
				DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss.SSS"));
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123", localDateTime.toString());
	}

	@Test
	public void from() {
		LocalDateTime localDateTime = LocalDateTime.parse("2023-08-03T01:02:03");
		LocalDateTime result = LocalDateTime.from(localDateTime);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result.toString());
		
		localDateTime = LocalDateTime.parse("2023-08-03T01:02:03");
		ZoneOffset zoneOffset = ZoneOffset.of("+09:00");
		OffsetDateTime offsetDateTime = OffsetDateTime.of(localDateTime, zoneOffset);
		System.out.println(offsetDateTime);
		result = LocalDateTime.from(offsetDateTime);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result.toString());

		ZonedDateTime zonedDateTime = ZonedDateTime.parse("2023-08-03T01:02:03+09:00[Asia/Tokyo]");
		result = LocalDateTime.from(zonedDateTime);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03", result.toString());
	}

	@Test
	public void ofInstant() {
		ZoneId zone = ZoneId.of("UTC+9");
		Instant instant = Instant.ofEpochSecond(1690992123L);
		LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		instant = Instant.ofEpochSecond(1690992123L, 123456789);
		localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123456789", localDateTime.toString());
	}

	@Test
	public void toEpochSecond() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3);
		ZoneOffset zoneOffset = ZoneOffset.of("+09:00");
		long result = localDateTime.toEpochSecond(zoneOffset);
		System.out.println(result);
		assertEquals(1690992123L, result);

		localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		zoneOffset = ZoneOffset.of("+09:00");
		result = localDateTime.toEpochSecond(zoneOffset);
		System.out.println(result);
		assertEquals(1690992123L, result);
	}

	@Test
	public void toEpochMilli() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3);
		ZoneId zone = ZoneId.of("UTC+9");
		Instant instant = localDateTime.atZone(zone).toInstant();
		long result = instant.toEpochMilli();
		System.out.println(result);
		assertEquals(1690992123000L, result);

		localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		zone = ZoneId.of("UTC+9");
		instant = localDateTime.atZone(zone).toInstant();
		result = instant.toEpochMilli();
		System.out.println(result);
		assertEquals(1690992123123L, result);
	}

	@Test
	public void ofEpochSecond() {
		ZoneOffset zoneOffset = ZoneOffset.of("+09:00");
		LocalDateTime localDateTime = LocalDateTime.ofEpochSecond(1690992123L, 0, zoneOffset);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		localDateTime = LocalDateTime.ofEpochSecond(1690992123L, 123456789, zoneOffset);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123456789", localDateTime.toString());
	}

	@Test
	public void ofEpochMilli() {
		ZoneId zone = ZoneId.of("UTC+9");
		Instant instant = Instant.ofEpochMilli(1690992123000L);
		LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		instant = Instant.ofEpochMilli(1690992123123L);
		localDateTime = LocalDateTime.ofInstant(instant, zone);
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123", localDateTime.toString());
	}

	@Test
	public void timestamp() {
		LocalDateTime localDateTime = new Timestamp(1690995723000L).toLocalDateTime();
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03", localDateTime.toString());

		localDateTime = new Timestamp(1690995723123L).toLocalDateTime();
		System.out.println(localDateTime);
		assertEquals("2023-08-03T01:02:03.123", localDateTime.toString());
	}

	@Test
	public void truncatedTo() {
		LocalDateTime localDateTime = LocalDateTime.of(2023, 8, 3, 1, 2, 3, 123456789);
		LocalDateTime result = localDateTime.truncatedTo(ChronoUnit.HOURS);
		System.out.println(result);
		assertEquals("2023-08-03T01:00", result.toString());

		result = localDateTime.truncatedTo(ChronoUnit.DAYS);
		System.out.println(result);
		assertEquals("2023-08-03T00:00", result.toString());
		
		result = localDateTime.truncatedTo(ChronoUnit.MILLIS);
		System.out.println(result);
		assertEquals("2023-08-03T01:02:03.123", result.toString());
	}
}

心得分享

Java LocalDateTime Example 提供了一組日期和時間相關的 API ，物件的值不會被改變，可以同時在不同的執行緒下被使用，提供了幾種 LocalDateTime 常見方法的操作範例，在應用上相當廣泛，熟悉 Java LocalDateTime 這些方法的操作，像是： format 、 parse 、 ofInstant 等方法。