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Java タイムスタンプヘルパー

Java の日付、カレンダー、およびタイムスタンプの例

Java Timestamp Examples

Complete guide to working with timestamps in Java. Modern Java 8+ API and legacy approaches.

Get Current Timestamp

Get current Unix timestamp in milliseconds and seconds

// Method 1: System.currentTimeMillis() (Recommended)
long timestampMs = System.currentTimeMillis();
System.out.println(timestampMs); // 1729584000000

// Method 2: Instant.now() (Java 8+)
import java.time.Instant;
long timestampMs2 = Instant.now().toEpochMilli();

// Get timestamp in seconds
long timestampSec = System.currentTimeMillis() / 1000;
// Or using Instant
long timestampSec2 = Instant.now().getEpochSecond();

Convert Timestamp to Date

Convert Unix timestamp to Date object

import java.util.Date;
import java.time.Instant;

// From milliseconds (legacy Date)
Date date = new Date(1729584000000L);
System.out.println(date); // Mon Oct 22 01:20:00 UTC 2024

// From seconds (convert to milliseconds)
Date dateFromSec = new Date(1729584000L * 1000);

// Using Instant (Java 8+, recommended)
Instant instant = Instant.ofEpochMilli(1729584000000L);
System.out.println(instant); // 2024-10-22T01:20:00Z

// From seconds using Instant
Instant instantFromSec = Instant.ofEpochSecond(1729584000L);

Date to Timestamp Conversion

Convert Date objects to Unix timestamps

import java.util.Date;
import java.time.LocalDateTime;
import java.time.ZoneId;

// Legacy Date to timestamp
Date date = new Date();
long timestamp = date.getTime();

// LocalDateTime to timestamp (Java 8+)
LocalDateTime ldt = LocalDateTime.now();
long timestampMs = ldt.atZone(ZoneId.systemDefault())
                      .toInstant()
                      .toEpochMilli();

// Specific date to timestamp
LocalDateTime specific = LocalDateTime.of(2024, 10, 22, 1, 20, 0);
long specificTimestamp = specific.atZone(ZoneId.of("UTC"))
                                 .toInstant()
                                 .toEpochMilli();

Quick Reference

Get Current Timestamp

System.currentTimeMillis()Instant.now().toEpochMilli()Instant.now().getEpochSecond()

Parse Timestamp

new Date(timestamp)Instant.ofEpochMilli(ms)Instant.ofEpochSecond(sec)

Format Date

DateTimeFormatter.ISO_INSTANTofPattern("yyyy-MM-dd")SimpleDateFormat (legacy)

Common Classes

Instant (UTC point in time)ZonedDateTime (with TZ)LocalDateTime (no TZ)