Unix Timestamp and Epoch in Java

Unix time counts elapsed time from the Unix epoch at 1970-01-01T00:00:00Z. Different ecosystems use different units, so always label whether a value is in seconds, milliseconds, microseconds, or nanoseconds.

Quick Start#

The following example uses the standard Java API or a widely used package for this task.

Quick start#

1import java.time.Instant;23Instant now = Instant.now();4long seconds = now.getEpochSecond();5long milliseconds = now.toEpochMilli();6System.out.println(seconds);7System.out.println(milliseconds);

Common Operations#

This second pattern covers a common production operation or a safer way to handle real input.

Convert back to ISO-8601#

1Instant instant = Instant.ofEpochSecond(epochSeconds);2System.out.println(instant);34Instant fromMs = Instant.ofEpochMilli(epochMilliseconds);

Important Notes#

Use Instant for a moment on the UTC timeline and ZonedDateTime only when you need presentation/business rules in a named timezone.

Best Practices#

1. Treat external input as untrusted and handle parse/validation errors explicitly.
2. Keep encoding, units, formats, and library-specific mapping rules explicit at system boundaries.
3. Add test vectors that cover empty input, Unicode text, malformed input, and representative production data.

References#

• POSIX Seconds Since the Epoch
• Java API Documentation