How to Convert Between java.util.Date and java.time Types?

How to Convert java.util.Date to java.time Types

Question: How do I convert java.util.Date or java.util.Calendar objects to the appropriate java.time framework types?

Answer:

From java.util.Date to Instant

To convert a java.util.Date to an Instant, use the toInstant method:

<code class="java">Instant instant = myUtilDate.toInstant();</code>

From java.util.Calendar to Instant

For java.util.Calendar objects, use the toInstant method:

<code class="java">Instant instant = myUtilCalendar.toInstant();</code>

From java.util.GregorianCalendar to ZonedDateTime

To convert a java.util.GregorianCalendar to a ZonedDateTime, use the toZonedDateTime method:

<code class="java">if (myUtilCalendar instanceof GregorianCalendar) {
    GregorianCalendar gregCal = (GregorianCalendar) myUtilCalendar;
    ZonedDateTime zdt = gregCal.toZonedDateTime();
}</code>

From OffsetDateTime to java.util.Date

Extract an Instant from the OffsetDateTime and use it to create a java.util.Date:

<code class="java">java.util.Date myUtilDate = java.util.Date.from(odt.toInstant());</code>

From ZonedDateTime to java.util.Date

Similarly, extract an Instant from the ZonedDateTime:

<code class="java">java.util.Date myUtilDate = java.util.Date.from(zdt.toInstant());</code>

From ZonedDateTime to GregorianCalendar

Convert a ZonedDateTime to a GregorianCalendar using the from method:

<code class="java">java.util.Calendar myUtilCalendar = java.util.GregorianCalendar.from(zdt);</code>

From LocalDate to ZonedDateTime

Going from a LocalDate to a ZonedDateTime requires specifying a time zone:

<code class="java">LocalDate localDate = zdt.toLocalDate();
ZonedDateTime zdt = localDate.atStartOfDay(zoneId);</code>

From LocalTime to ZonedDateTime

Similarly, for LocalTime:

<code class="java">LocalTime localTime = zdt.toLocalTime();
ZonedDateTime zdt = ZonedDateTime.of(localDate, localTime, zoneId);</code>

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