[BAEL-8227] Convert between Timestamp and DateTime (#17123)

Co-authored-by: rajatgarg <[email protected]>

Author: rajat-garg

core-java-modules/core-java-datetime-conversion-2/src/main/java/com/baeldung/convertdatetimeandtimestamp/DateTimeAndTimestampConverter.java

@@ -0,0 +1,40 @@
+package com.baeldung.convertdatetimeandtimestamp;
+
+import java.sql.Timestamp;
+import java.time.Instant;
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+
+import org.joda.time.DateTime;
+
+public class DateTimeAndTimestampConverter {
+
+    public static DateTime convertToDateTimeUsingConstructor(Timestamp timestamp) {
+        return new DateTime(timestamp.getTime());
+    }
+
+    public static DateTime convertToDateTimeUsingInstant(Timestamp timestamp) {
+        Instant instant = timestamp.toInstant();
+        return new DateTime(instant.toEpochMilli());
+    }
+
+    public static DateTime convertToDateTimeUsingLocalDateTime(Timestamp timestamp) {
+        LocalDateTime localDateTime = timestamp.toLocalDateTime();
+        return new DateTime(localDateTime.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli());
+    }
+
+    public static Timestamp convertToTimestampUsingConstructor(DateTime dateTime) {
+        return new Timestamp(dateTime.getMillis());
+    }
+
+    public static Timestamp convertToTimestampUsingInstant(DateTime dateTime) {
+        Instant instant = Instant.ofEpochMilli(dateTime.getMillis());
+        return Timestamp.from(instant);
+    }
+
+    public static Timestamp convertToTimestampUsingLocalDateTime(DateTime dateTime) {
+        Instant instant = Instant.ofEpochMilli(dateTime.getMillis());
+        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
+        return Timestamp.valueOf(localDateTime);
+    }
+}

core-java-modules/core-java-datetime-conversion-2/src/test/java/com/baeldung/convertdatetimeandtimestamp/DateTimeAndTimestampConverterUnitTest.java

@@ -0,0 +1,65 @@
+package com.baeldung.convertdatetimeandtimestamp;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.sql.Timestamp;
+import org.joda.time.DateTime;
+import org.junit.jupiter.api.Test;
+
+
+public class DateTimeAndTimestampConverterUnitTest {
+
+    @Test
+    public void givenTimestamp_whenUsingConstructor_thenConvertToDateTime() {
+        long currentTimeMillis = System.currentTimeMillis();
+        Timestamp timestamp = new Timestamp(currentTimeMillis);
+        DateTime expectedDateTime = new DateTime(currentTimeMillis);
+        DateTime convertedDateTime = DateTimeAndTimestampConverter.convertToDateTimeUsingConstructor(timestamp);
+        assertEquals(expectedDateTime, convertedDateTime);
+    }
+
+    @Test
+    public void givenTimestamp_whenUsingInstant_thenConvertToDateTime() {
+        long currentTimeMillis = System.currentTimeMillis();
+        Timestamp timestamp = new Timestamp(currentTimeMillis);
+        DateTime expectedDateTime = new DateTime(currentTimeMillis);
+        DateTime convertedDateTime = DateTimeAndTimestampConverter.convertToDateTimeUsingInstant(timestamp);
+        assertEquals(expectedDateTime, convertedDateTime);
+    }
+
+    @Test
+    public void givenTimestamp_whenUsingLocalDateTime_thenConvertToDateTime() {
+        long currentTimeMillis = System.currentTimeMillis();
+        Timestamp timestamp = new Timestamp(currentTimeMillis);
+        DateTime expectedDateTime = new DateTime(currentTimeMillis);
+        DateTime convertedDateTime = DateTimeAndTimestampConverter.convertToDateTimeUsingLocalDateTime(timestamp);
+        assertEquals(expectedDateTime, convertedDateTime);
+    }
+
+    @Test
+    public void givenDateTime_whenUsingConstructor_thenConvertToTimestamp() {
+        long currentTimeMillis = System.currentTimeMillis();
+        DateTime dateTime = new DateTime(currentTimeMillis);
+        Timestamp expectedTimestamp = new Timestamp(currentTimeMillis);
+        Timestamp convertedTimestamp = DateTimeAndTimestampConverter.convertToTimestampUsingConstructor(dateTime);
+        assertEquals(expectedTimestamp, convertedTimestamp);
+    }
+
+    @Test
+    public void givenDateTime_whenUsingInstant_thenConvertToTimestamp() {
+        long currentTimeMillis = System.currentTimeMillis();
+        DateTime dateTime = new DateTime(currentTimeMillis);
+        Timestamp expectedTimestamp = new Timestamp(currentTimeMillis);
+        Timestamp convertedTimestamp = DateTimeAndTimestampConverter.convertToTimestampUsingInstant(dateTime);
+        assertEquals(expectedTimestamp, convertedTimestamp);
+    }
+
+    @Test
+    public void givenDateTime_whenUsingLocalDateTime_thenConvertToTimestamp() {
+        long currentTimeMillis = System.currentTimeMillis();
+        DateTime dateTime = new DateTime(currentTimeMillis);
+        Timestamp expectedTimestamp = new Timestamp(currentTimeMillis);
+        Timestamp convertedTimestamp = DateTimeAndTimestampConverter.convertToTimestampUsingLocalDateTime(dateTime);
+        assertEquals(expectedTimestamp, convertedTimestamp);
+    }
+}