Localdate to java.util.Date and vice versa simplest conversion?

java

date-time-api

timezone

java-8

byNikita Barsukov·Sep 25, 2024

Convert LocalDate to java.util.Date using Date.from(localDate.atStartOfDay(ZoneId.systemDefault()).toInstant()), and convert java.util.Date to LocalDate using date.toInstant().atZone(ZoneId.systemDefault()).toLocalDate().

To java.util.Date:

LocalDate localDate = LocalDate.now();
// Hey there, I'm just your local date. No BS just YYYY-MM-DD!
java.util.Date date = java.sql.Date.valueOf(localDate);

To LocalDate:

java.util.Date date = new java.util.Date();
// Time to ditch this old fella and get back to our local!
LocalDate localDate = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();

Mastering TimeZone: Precision is key

When performing this transformation, understanding TimeZone is crucial. LocalDate doesn't carry time or timezone info, but java.util.Date is precisely a point on the global UTC timeline.

Converting LocalDate to java.util.Date means assuming a specific time (usually start of the day) in a specified timezone:

ZoneId desiredZone = ZoneId.of("America/New_York"); //Ny, Ny, a city so nice they named it twice
java.util.Date dateFromLocalDate = Date.from(localDate.atStartOfDay(desiredZone).toInstant());
LocalDate localDateFromDate = date.toInstant().atZone(desiredZone).toLocalDate();

Out with the old

java.util.Date is part of the old date-time classes with known design issues. Since Java 8, the java.time package brings modern date-time API with classes providing better usability:

LocalDate localDateWithTime = date.toInstant()
                                   .atZone(ZoneId.systemDefault())
                                   .toLocalDateTime() // hello there, modern date-time API!
                                   .toLocalDate();

Dealing with legacy: Java.util.Date

While the transition to java.time is recommended for better functionality, sometimes you might still need to work with java.util.Date:

Backports: Libraries like ThreeTen-Backport and ThreeTenABP (for Android) provide similar java.time functionality, even for Java 6 & 7.

Best Practices

Remember the time zone when converting from LocalDate to java.util.Date.
Specify an explicit time zone instead of relying on the system's default.
Avoid old date-time classes; if necessary, use the simplest possible conversion patterns.
Use Instant and ZonedDateTime to conveniently handle precise moments and timezones.
Utilize backports if you're stuck with legacy versions of Java.

Pitfalls and Warnings

While our methods work seamlessly for most cases, edge cases will inevitably occur:

DST Transitions: Daylight Saving Time can cause anomalies; verify after conversion.
Leap Seconds: java.util.Date is oblivious of Leap seconds.
Ambiguous Time Zones: Three-letter time zone abbreviations can be misleading; stick to region names.
Java.sql.Date limitations: java.sql.Date.valueOf(localDate) only converts the date part, not time.