BAEL-7614 sql.Timestamp to java.util.Calendar conversion

core-java-modules/core-java-datetime-conversion-2/src/main/java/com/baeldung/timestamptocalendar/SqlTimestampToCalendarConverter.java

@@ -0,0 +1,17 @@
+package com.baeldung.timestamptocalendar;
+
+import java.sql.Timestamp;
+import java.util.Calendar;
+
+public class SqlTimestampToCalendarConverter {
+
+    public static Calendar timestampToCalendar(Timestamp timestamp) {
+        Calendar calendar = Calendar.getInstance();
+        calendar.setTimeInMillis(timestamp.getTime());
+        return calendar;
+    }
+
+    public static Timestamp calendarToTimestamp(Calendar calendar) {
+        return new Timestamp(calendar.getTimeInMillis());
+    }
+}

core-java-modules/core-java-datetime-conversion-2/src/test/java/com/baeldung/timestamptocalendar/SqlTimestampToCalendarConverterUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.timestamptocalendar;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
+import java.sql.Timestamp;
+import java.util.Calendar;
+
+import org.junit.Test;
+
+public class SqlTimestampToCalendarConverterUnitTest {
+
+    @Test
+    public void givenTimestamp_whenConvertToCalendar_thenEqualMillis() {
+        Timestamp timestamp = new Timestamp(1713544200801L);
+        Calendar calendar = SqlTimestampToCalendarConverter.timestampToCalendar(timestamp);
+        assertEquals(calendar.getTimeInMillis(), timestamp.getTime());
+    }
+
+    @Test
+    public void givenCalendarFromTimestamp_whenConvertBackToTimestamp_thenEqualMillis() {
+        Timestamp timestamp = new Timestamp(1713544200801L);
+        Calendar calendar = SqlTimestampToCalendarConverter.timestampToCalendar(timestamp);
+        timestamp = SqlTimestampToCalendarConverter.calendarToTimestamp(calendar);
+        assertEquals(calendar.getTimeInMillis(), timestamp.getTime());
+    }
+
+    @Test
+    public void givenTimestamp_whenConvertToCalendarAndBack_thenLoseNanos() {
+        int nanos = 801789562;
+        int losslessNanos = 801000000;
+        Timestamp timestamp = new Timestamp(1713544200801L);
+        timestamp.setNanos(nanos);
+        assertEquals(nanos, timestamp.getNanos());
+        Calendar calendar = SqlTimestampToCalendarConverter.timestampToCalendar(timestamp);
+        timestamp = SqlTimestampToCalendarConverter.calendarToTimestamp(calendar);
+        assertEquals(losslessNanos, timestamp.getNanos());
+    }
+}