Epoch Millisecond Subtraction Bug (1927)

Java's Date and Calendar classes are notoriously buggy with dates before 1970. Subtracting epoch milliseconds for dates in 1927 (pre-Unix epoch) yields incorrect results due to limitations in their implementation. The issue isn't with the subtraction itself, but the underlying representation of the dates.

Solution: Use java.time (Java 8+). It handles dates far beyond the Unix epoch's limitations reliably.

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.temporal.ChronoUnit;

public class EpochDiff {
    public static void main(String[] args) {
        LocalDateTime date1927 = LocalDateTime.of(1927, 1, 1, 0, 0);
        LocalDateTime date2024 = LocalDateTime.of(2024, 1, 1, 0, 0);

        Instant instant1927 = date1927.atZone(ZoneId.systemDefault()).toInstant();
        Instant instant2024 = date2024.atZone(ZoneId.systemDefault()).toInstant();

        long diffSeconds = ChronoUnit.SECONDS.between(instant1927, instant2024);
        long diffMillis = ChronoUnit.MILLIS.between(instant1927, instant2024);

        System.out.println("Difference in seconds: " + diffSeconds);
        System.out.println("Difference in milliseconds: " + diffMillis);
    }
}

This code accurately calculates the difference using java.time. Replace ZoneId.systemDefault() with a specific ZoneId if necessary for precision. Spring Boot applications benefit directly from this improved date/time handling. Avoid Date and Calendar for anything beyond basic, modern date/time operations.