#BAEL-16646 flatten java-datetime modules

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/date/validation/DateValidator.java

@@ -0,0 +1,5 @@
+package com.baeldung.date.validation;
+
+public interface DateValidator {
+   boolean isValid(String dateStr);
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/date/validation/DateValidatorUsingApacheValidator.java

@@ -0,0 +1,11 @@
+package com.baeldung.date.validation;
+
+import org.apache.commons.validator.GenericValidator;
+
+public class DateValidatorUsingApacheValidator implements DateValidator {
+
+    @Override
+    public boolean isValid(String dateStr) {
+        return GenericValidator.isDate(dateStr, "yyyy-MM-dd", true); 
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/date/validation/DateValidatorUsingDateFormat.java

@@ -0,0 +1,25 @@
+package com.baeldung.date.validation;
+
+import java.text.DateFormat;
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+
+public class DateValidatorUsingDateFormat implements DateValidator {
+    private String dateFormat;
+
+    public DateValidatorUsingDateFormat(String dateFormat) {
+        this.dateFormat = dateFormat;
+    }
+
+    @Override
+    public boolean isValid(String dateStr) {
+        DateFormat sdf = new SimpleDateFormat(this.dateFormat);
+        sdf.setLenient(false);
+        try {
+            sdf.parse(dateStr);
+        } catch (ParseException e) {
+            return false;
+        }
+        return true;
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/date/validation/DateValidatorUsingDateTimeFormatter.java

@@ -0,0 +1,22 @@
+package com.baeldung.date.validation;
+
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+
+public class DateValidatorUsingDateTimeFormatter implements DateValidator {
+    private DateTimeFormatter dateFormatter;
+    
+    public DateValidatorUsingDateTimeFormatter(DateTimeFormatter dateFormatter) {
+        this.dateFormatter = dateFormatter;
+    }
+
+    @Override
+    public boolean isValid(String dateStr) {
+        try {
+            this.dateFormatter.parse(dateStr);
+        } catch (DateTimeParseException e) {
+            return false;
+        }
+        return true;
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/date/validation/DateValidatorUsingLocalDate.java

@@ -0,0 +1,23 @@
+package com.baeldung.date.validation;
+
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+
+public class DateValidatorUsingLocalDate implements DateValidator {
+    private DateTimeFormatter dateFormatter;
+    
+    public DateValidatorUsingLocalDate(DateTimeFormatter dateFormatter) {
+        this.dateFormatter = dateFormatter;
+    }
+
+    @Override
+    public boolean isValid(String dateStr) {
+        try {
+            LocalDate.parse(dateStr, this.dateFormatter);
+        } catch (DateTimeParseException e) {
+            return false;
+        }
+        return true;
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/DateMatcher.java

@@ -0,0 +1,7 @@
+package com.baeldung.regexp.datepattern;
+
+public interface DateMatcher {
+
+    boolean matches(String date);
+
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/FormattedDateMatcher.java

@@ -0,0 +1,14 @@
+package com.baeldung.regexp.datepattern;
+
+import java.util.regex.Pattern;
+
+class FormattedDateMatcher implements DateMatcher {
+
+    private static final Pattern DATE_PATTERN = Pattern.compile(
+            "^\\d{4}-\\d{2}-\\d{2}$");
+
+    @Override
+    public boolean matches(String date) {
+        return DATE_PATTERN.matcher(date).matches();
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/RangedDateMatcher.java

@@ -0,0 +1,14 @@
+package com.baeldung.regexp.datepattern;
+
+import java.util.regex.Pattern;
+
+class RangedDateMatcher implements DateMatcher {
+
+    private static final Pattern DATE_PATTERN = Pattern.compile(
+            "^((19|2[0-9])[0-9]{2})-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])$");
+
+    @Override
+    public boolean matches(String date) {
+        return DATE_PATTERN.matcher(date).matches();
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/gregorian/February29thMatcher.java

@@ -0,0 +1,16 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+
+import java.util.regex.Pattern;
+
+public class February29thMatcher implements DateMatcher {
+
+    private static final Pattern DATE_PATTERN = Pattern.compile(
+            "^((2000|2400|2800|(19|2[0-9](0[48]|[2468][048]|[13579][26])))-02-29)$");
+
+    @Override
+    public boolean matches(String date) {
+        return DATE_PATTERN.matcher(date).matches();
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/gregorian/FebruaryGeneralMatcher.java

@@ -0,0 +1,16 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+
+import java.util.regex.Pattern;
+
+public class FebruaryGeneralMatcher implements DateMatcher {
+
+    private static final Pattern DATE_PATTERN = Pattern.compile(
+            "^(((19|2[0-9])[0-9]{2})-02-(0[1-9]|1[0-9]|2[0-8]))$");
+
+    @Override
+    public boolean matches(String date) {
+        return DATE_PATTERN.matcher(date).matches();
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/gregorian/GregorianDateMatcher.java

@@ -0,0 +1,19 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+
+import java.util.regex.Pattern;
+
+class GregorianDateMatcher implements DateMatcher {
+
+    private static final Pattern DATE_PATTERN = Pattern.compile(
+            "^((2000|2400|2800|(19|2[0-9](0[48]|[2468][048]|[13579][26])))-02-29)$" 
+            + "|^(((19|2[0-9])[0-9]{2})-02-(0[1-9]|1[0-9]|2[0-8]))$"
+            + "|^(((19|2[0-9])[0-9]{2})-(0[13578]|10|12)-(0[1-9]|[12][0-9]|3[01]))$" 
+            + "|^(((19|2[0-9])[0-9]{2})-(0[469]|11)-(0[1-9]|[12][0-9]|30))$");
+
+    @Override
+    public boolean matches(String date) {
+        return DATE_PATTERN.matcher(date).matches();
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/gregorian/MonthsOf30DaysMatcher.java

@@ -0,0 +1,17 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+
+import java.util.regex.Pattern;
+
+public class MonthsOf30DaysMatcher implements DateMatcher {
+
+    private static final Pattern DATE_PATTERN = Pattern.compile(
+            "^(((19|2[0-9])[0-9]{2})-(0[469]|11)-(0[1-9]|[12][0-9]|30))$");
+
+    @Override
+    public boolean matches(String date) {
+        return DATE_PATTERN.matcher(date).matches();
+    }
+
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/gregorian/MonthsOf31DaysMatcher.java

@@ -0,0 +1,17 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+
+import java.util.regex.Pattern;
+
+public class MonthsOf31DaysMatcher implements DateMatcher {
+
+    private static final Pattern DATE_PATTERN = Pattern.compile(
+            "^(((19|2[0-9])[0-9]{2})-(0[13578]|10|12)-(0[1-9]|[12][0-9]|3[01]))$");
+
+    @Override
+    public boolean matches(String date) {
+        return DATE_PATTERN.matcher(date).matches();
+    }
+
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/regexp/datepattern/optmization/OptimizedMatcher.java

@@ -0,0 +1,6 @@
+package com.baeldung.regexp.datepattern.optmization;
+
+public class OptimizedMatcher {
+
+
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplay.java

@@ -0,0 +1,55 @@
+package com.baeldung.timezonedisplay;
+
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.ZoneOffset;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public class TimezoneDisplay {
+
+    public enum OffsetBase {
+        GMT, UTC
+    }
+
+    public List<String> getTimeZoneList(OffsetBase base) {
+        Set<String> availableZoneIds = ZoneId.getAvailableZoneIds();
+
+        LocalDateTime now = LocalDateTime.now();
+        return availableZoneIds
+          .stream()
+          .map(ZoneId::of)
+          .sorted(new ZoneComparator())
+          .map(id -> String.format("(%s%s) %s", base, getOffset(now, id), id.getId()))
+          .collect(Collectors.toList());
+    }
+
+    private String getOffset(LocalDateTime dateTime, ZoneId id) {
+        return dateTime
+          .atZone(id)
+          .getOffset()
+          .getId()
+          .replace("Z", "+00:00");
+    }
+
+    private class ZoneComparator implements Comparator<ZoneId> {
+
+        @Override
+        public int compare(ZoneId zoneId1, ZoneId zoneId2) {
+            LocalDateTime now = LocalDateTime.now();
+
+            ZoneOffset offset1 = now
+              .atZone(zoneId1)
+              .getOffset();
+
+            ZoneOffset offset2 = now
+              .atZone(zoneId2)
+              .getOffset();
+
+            return offset1.compareTo(offset2);
+        }
+    }
+
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayApp.java

@@ -0,0 +1,18 @@
+package com.baeldung.timezonedisplay;
+
+import java.util.List;
+
+public class TimezoneDisplayApp {
+
+    public static void main(String... args) {
+        TimezoneDisplay display = new TimezoneDisplay();
+
+        System.out.println("Time zones in UTC:");
+        List<String> utc = display.getTimeZoneList(TimezoneDisplay.OffsetBase.UTC);
+        utc.forEach(System.out::println);
+
+        System.out.println("Time zones in GMT:");
+        List<String> gmt = display.getTimeZoneList(TimezoneDisplay.OffsetBase.GMT);
+        gmt.forEach(System.out::println);
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayJava7.java

@@ -0,0 +1,43 @@
+package com.baeldung.timezonedisplay;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.TimeZone;
+import java.util.concurrent.TimeUnit;
+
+public class TimezoneDisplayJava7 {
+
+    public enum OffsetBase {
+        GMT, UTC
+    }
+
+    public List<String> getTimeZoneList(TimezoneDisplayJava7.OffsetBase base) {
+        String[] availableZoneIds = TimeZone.getAvailableIDs();
+        List<String> result = new ArrayList<>(availableZoneIds.length);
+
+        for (String zoneId : availableZoneIds) {
+            TimeZone curTimeZone = TimeZone.getTimeZone(zoneId);
+
+            String offset = calculateOffset(curTimeZone.getRawOffset());
+
+            result.add(String.format("(%s%s) %s", base, offset, zoneId));
+        }
+
+        Collections.sort(result);
+
+        return result;
+    }
+
+    private String calculateOffset(int rawOffset) {
+        if (rawOffset == 0) {
+            return "+00:00";
+        }
+        long hours = TimeUnit.MILLISECONDS.toHours(rawOffset);
+        long minutes = TimeUnit.MILLISECONDS.toMinutes(rawOffset);
+        minutes = Math.abs(minutes - TimeUnit.HOURS.toMinutes(hours));
+
+        return String.format("%+03d:%02d", hours, Math.abs(minutes));
+    }
+
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayJava7App.java

@@ -0,0 +1,23 @@
+package com.baeldung.timezonedisplay;
+
+import java.util.List;
+
+public class TimezoneDisplayJava7App {
+
+    public static void main(String... args) {
+        TimezoneDisplayJava7 display = new TimezoneDisplayJava7();
+
+        System.out.println("Time zones in UTC:");
+        List<String> utc = display.getTimeZoneList(TimezoneDisplayJava7.OffsetBase.UTC);
+        for (String timeZone : utc) {
+            System.out.println(timeZone);
+        }
+
+        System.out.println("Time zones in GMT:");
+        List<String> gmt = display.getTimeZoneList(TimezoneDisplayJava7.OffsetBase.GMT);
+        for (String timeZone : gmt) {
+            System.out.println(timeZone);
+        }
+    }
+
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/zonedatetime/OffsetDateTimeExample.java

@@ -0,0 +1,13 @@
+package com.baeldung.zonedatetime;
+
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+
+public class OffsetDateTimeExample {
+
+    public OffsetDateTime getCurrentTimeByZoneOffset(String offset) {
+        ZoneOffset zoneOffSet= ZoneOffset.of(offset);
+        OffsetDateTime date = OffsetDateTime.now(zoneOffSet);
+        return date;
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/zonedatetime/OffsetTimeExample.java

@@ -0,0 +1,13 @@
+package com.baeldung.zonedatetime;
+
+import java.time.OffsetTime;
+import java.time.ZoneOffset;
+
+public class OffsetTimeExample {
+
+    public OffsetTime getCurrentTimeByZoneOffset(String offset) {
+        ZoneOffset zoneOffSet = ZoneOffset.of(offset);
+        OffsetTime time = OffsetTime.now(zoneOffSet);
+        return time;
+    }
+}

core-java-modules/core-java-datetime-string/src/main/java/com/baeldung/zonedatetime/ZoneDateTimeExample.java

@@ -0,0 +1,21 @@
+package com.baeldung.zonedatetime;
+
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+
+public class ZoneDateTimeExample {
+
+    public ZonedDateTime getCurrentTimeByZoneId(String region) {
+        ZoneId zone = ZoneId.of(region);
+        ZonedDateTime date = ZonedDateTime.now(zone);
+        return date;
+    }
+
+    public ZonedDateTime convertZonedDateTime(ZonedDateTime sourceDate, String destZone) {
+
+        ZoneId destZoneId = ZoneId.of(destZone);
+        ZonedDateTime destDate = sourceDate.withZoneSameInstant(destZoneId);
+
+        return destDate;
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/date/StringToDateUnitTest.java

@@ -0,0 +1,141 @@
+package com.baeldung.date;
+
+import static org.junit.Assert.assertEquals;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.GregorianCalendar;
+import java.util.Locale;
+
+import org.apache.commons.lang3.time.DateUtils;
+import org.joda.time.DateTime;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+public class StringToDateUnitTest {
+
+    @Rule
+    public ExpectedException thrown = ExpectedException.none();
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetCorrectLocalDate() {
+        LocalDate expectedLocalDate = LocalDate.of(2018, 05, 05);
+
+        LocalDate date = LocalDate.parse("2018-05-05");
+
+        assertThat(date).isEqualTo(expectedLocalDate);
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetCorrectLocalDateTime() {
+        LocalDateTime expectedLocalDateTime = LocalDateTime.of(2018, 05, 05, 11, 50, 55);
+
+        LocalDateTime dateTime = LocalDateTime.parse("2018-05-05T11:50:55");
+
+        assertThat(dateTime).isEqualTo(expectedLocalDateTime);
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetDateTimeParseException() {
+        thrown.expect(DateTimeParseException.class);
+        thrown.expectMessage("Text '2018-05-05' could not be parsed at index 10");
+
+        LocalDateTime.parse("2018-05-05");
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetCorrectZonedDateTime() {
+        LocalDateTime localDateTime = LocalDateTime.of(2015, 05, 05, 10, 15, 30);
+        ZonedDateTime expectedZonedDateTime = ZonedDateTime.of(localDateTime, ZoneId.of("Europe/Paris"));
+
+        ZonedDateTime zonedDateTime = ZonedDateTime.parse("2015-05-05T10:15:30+01:00[Europe/Paris]");
+
+        assertThat(zonedDateTime).isEqualTo(expectedZonedDateTime);
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDateUsingFormatter_thenWeGetCorrectLocalDate() {
+        LocalDate expectedLocalDate = LocalDate.of(1959, 7, 9);
+
+        String dateInString = "19590709";
+        LocalDate date = LocalDate.parse(dateInString, DateTimeFormatter.BASIC_ISO_DATE);
+
+        assertThat(date).isEqualTo(expectedLocalDate);
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDateUsingCustomFormatter_thenWeGetCorrectLocalDate() {
+        LocalDate expectedLocalDate = LocalDate.of(1980, 05, 05);
+
+        String dateInString = "Mon, 05 May 1980";
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE, d MMM yyyy", Locale.ENGLISH);
+        LocalDate dateTime = LocalDate.parse(dateInString, formatter);
+
+        assertThat(dateTime).isEqualTo(expectedLocalDate);
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetCorrectDate() throws ParseException {
+        SimpleDateFormat formatter = new SimpleDateFormat("dd-MMM-yyyy", Locale.ENGLISH);
+
+        String dateInString = "7-Jun-2013";
+        Date date = formatter.parse(dateInString);
+
+        assertDateIsCorrect(date);
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetParseException() throws ParseException {
+        SimpleDateFormat formatter = new SimpleDateFormat("dd-MMM-yyyy", Locale.ENGLISH);
+
+        thrown.expect(ParseException.class);
+        thrown.expectMessage("Unparseable date: \"07/06/2013\"");
+
+        String dateInString = "07/06/2013";
+        formatter.parse(dateInString);
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetCorrectJodaDateTime() {
+        org.joda.time.format.DateTimeFormatter formatter = org.joda.time.format.DateTimeFormat.forPattern("dd/MM/yyyy HH:mm:ss");
+
+        String dateInString = "07/06/2013 10:11:59";
+        DateTime dateTime = DateTime.parse(dateInString, formatter);
+
+        assertEquals("Day of Month should be 7: ", 7, dateTime.getDayOfMonth());
+        assertEquals("Month should be: ", 6, dateTime.getMonthOfYear());
+        assertEquals("Year should be: ", 2013, dateTime.getYear());
+
+        assertEquals("Hour of day should be: ", 10, dateTime.getHourOfDay());
+        assertEquals("Minutes of hour should be: ", 11, dateTime.getMinuteOfHour());
+        assertEquals("Seconds of minute should be: ", 59, dateTime.getSecondOfMinute());
+    }
+
+    @Test
+    public void givenDateString_whenConvertedToDate_thenWeGetCorrectDateTime() throws ParseException {
+        String dateInString = "07/06-2013";
+        Date date = DateUtils.parseDate(dateInString, new String[] { "yyyy-MM-dd HH:mm:ss", "dd/MM-yyyy" });
+
+        assertDateIsCorrect(date);
+    }
+
+    private void assertDateIsCorrect(Date date) {
+        Calendar calendar = new GregorianCalendar(Locale.ENGLISH);
+        calendar.setTime(date);
+
+        assertEquals("Day of Month should be 7: ", 7, calendar.get(Calendar.DAY_OF_MONTH));
+        assertEquals("Month should be: ", 5, calendar.get(Calendar.MONTH));
+        assertEquals("Year should be: ", 2013, calendar.get(Calendar.YEAR));
+    }
+
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/date/validation/DateValidatorUsingApacheValidatorUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.commons.validator.GenericValidator;
+import org.junit.Test;
+
+public class DateValidatorUsingApacheValidatorUnitTest {
+
+    @Test
+    public void whenValidDatePassed_ThenTrue() {
+        assertTrue(GenericValidator.isDate("2019-02-28", "yyyy-MM-dd", true));
+    }
+
+    @Test
+    public void whenInvalidDatePassed_ThenFalse() {
+        assertFalse(GenericValidator.isDate("2019-02-29", "yyyy-MM-dd", true));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/date/validation/DateValidatorUsingDateFormatUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class DateValidatorUsingDateFormatUnitTest {
+    
+    @Test
+    public void givenValidator_whenValidDatePassed_ThenTrue() {
+        DateValidator validator = new DateValidatorUsingDateFormat("MM/dd/yyyy");
+        
+        assertTrue(validator.isValid("02/28/2019"));
+    }
+    
+    @Test
+    public void givenValidator_whenInvalidDatePassed_ThenFalse() {
+        DateValidator validator = new DateValidatorUsingDateFormat("MM/dd/yyyy");
+        
+        assertFalse(validator.isValid("02/30/2019"));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/date/validation/DateValidatorUsingDateTimeFormatterUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.time.format.DateTimeFormatter;
+import java.time.format.ResolverStyle;
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class DateValidatorUsingDateTimeFormatterUnitTest {
+    
+    @Test
+    public void givenValidator_whenValidDatePassed_ThenTrue() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("uuuu-MM-dd", Locale.US)
+            .withResolverStyle(ResolverStyle.STRICT);
+        DateValidator validator = new DateValidatorUsingDateTimeFormatter(dateFormatter);
+        
+        assertTrue(validator.isValid("2019-02-28"));
+    }
+    
+    @Test
+    public void givenValidator_whenInValidDatePassed_ThenFalse() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("uuuu-MM-dd", Locale.US)
+            .withResolverStyle(ResolverStyle.STRICT);
+        DateValidator validator = new DateValidatorUsingDateTimeFormatter(dateFormatter);
+        
+        assertFalse(validator.isValid("2019-02-30"));
+    }
+
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/date/validation/DateValidatorUsingLocalDateUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.date.validation;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.time.format.DateTimeFormatter;
+
+import org.junit.Test;
+
+public class DateValidatorUsingLocalDateUnitTest {
+    
+    @Test
+    public void givenValidator_whenValidDatePassed_ThenTrue() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.BASIC_ISO_DATE;
+        DateValidator validator = new DateValidatorUsingLocalDate(dateFormatter);
+        
+        assertTrue(validator.isValid("20190228"));
+    }
+    
+    @Test
+    public void givenValidator_whenInValidDatePassed_ThenFalse() {
+        DateTimeFormatter dateFormatter = DateTimeFormatter.BASIC_ISO_DATE;
+        DateValidator validator = new DateValidatorUsingLocalDate(dateFormatter);
+        
+        assertFalse(validator.isValid("20190230"));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/datetime/DateTimeFormatterUnitTest.java

@@ -0,0 +1,158 @@
+package com.baeldung.datetime;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.time.LocalTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.time.format.FormatStyle;
+import java.time.temporal.ChronoUnit;
+import java.util.Locale;
+import java.util.TimeZone;
+
+public class DateTimeFormatterUnitTest {
+
+    @Test
+    public void givenDefaultUsLocaleAndDateTimeAndPattern_whenFormatWithDifferentLocales_thenGettingLocalizedDateTimes() {
+        Locale.setDefault(Locale.US);
+        LocalDateTime localDateTime = LocalDateTime.of(2018, 1, 1, 10, 15, 50, 500);
+        String pattern = "dd-MMMM-yyyy HH:mm:ss.SSS";
+
+        DateTimeFormatter defaultTimeFormatter = DateTimeFormatter.ofPattern(pattern);
+        DateTimeFormatter plTimeFormatter = DateTimeFormatter.ofPattern(pattern, new Locale("pl", "PL"));
+        DateTimeFormatter deTimeFormatter = DateTimeFormatter.ofPattern(pattern).withLocale(Locale.GERMANY);
+
+        Assert.assertEquals("01-January-2018 10:15:50.000", defaultTimeFormatter.format(localDateTime));
+        Assert.assertEquals("01-stycznia-2018 10:15:50.000", plTimeFormatter.format(localDateTime));
+        Assert.assertEquals("01-Januar-2018 10:15:50.000", deTimeFormatter.format(localDateTime));
+    }
+
+    @Test
+    public void givenDateTimeAndTimeZone_whenFormatWithDifferentLocales_thenGettingLocalizedZonedDateTimes() {
+        Locale.setDefault(Locale.US);
+        LocalDateTime localDateTime = LocalDateTime.of(2018, 1, 1, 10, 15, 50, 500);
+        ZoneId losAngelesTimeZone = TimeZone.getTimeZone("America/Los_Angeles").toZoneId();
+
+        DateTimeFormatter localizedFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL);
+        DateTimeFormatter frLocalizedFormatter =
+                DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).withLocale(Locale.FRANCE);
+        String formattedDateTime = localizedFormatter.format(ZonedDateTime.of(localDateTime, losAngelesTimeZone));
+        String frFormattedDateTime = frLocalizedFormatter.format(ZonedDateTime.of(localDateTime, losAngelesTimeZone));
+
+        Assert.assertEquals("Monday, January 1, 2018 10:15:50 AM PST", formattedDateTime);
+        Assert.assertEquals("lundi 1 janvier 2018 10 h 15 PST", frFormattedDateTime);
+    }
+
+    @Test
+    public void shouldPrintFormattedDate() {
+        String europeanDatePattern = "dd.MM.yyyy";
+        DateTimeFormatter europeanDateFormatter = DateTimeFormatter.ofPattern(europeanDatePattern);
+        LocalDate summerDay = LocalDate.of(2016, 7, 31);
+        Assert.assertEquals("31.07.2016", europeanDateFormatter.format(summerDay));
+    }
+
+    @Test
+    public void shouldPrintFormattedTime24() {
+        String timeColonPattern = "HH:mm:ss";
+        DateTimeFormatter timeColonFormatter = DateTimeFormatter.ofPattern(timeColonPattern);
+        LocalTime colonTime = LocalTime.of(17, 35, 50);
+        Assert.assertEquals("17:35:50", timeColonFormatter.format(colonTime));
+    }
+
+    @Test
+    public void shouldPrintFormattedTimeWithMillis() {
+        String timeColonPattern = "HH:mm:ss SSS";
+        DateTimeFormatter timeColonFormatter = DateTimeFormatter.ofPattern(timeColonPattern);
+        LocalTime colonTime = LocalTime.of(17, 35, 50).plus(329, ChronoUnit.MILLIS);
+        Assert.assertEquals("17:35:50 329", timeColonFormatter.format(colonTime));
+    }
+
+    @Test
+    public void shouldPrintFormattedTimePM() {
+        String timeColonPattern = "hh:mm:ss a";
+        DateTimeFormatter timeColonFormatter = DateTimeFormatter.ofPattern(timeColonPattern);
+        LocalTime colonTime = LocalTime.of(17, 35, 50);
+        Assert.assertEquals("05:35:50 PM", timeColonFormatter.format(colonTime));
+    }
+
+    @Test
+    public void shouldPrintFormattedUTCRelatedZonedDateTime() {
+        String newYorkDateTimePattern = "dd.MM.yyyy HH:mm z";
+        DateTimeFormatter newYorkDateFormatter = DateTimeFormatter.ofPattern(newYorkDateTimePattern);
+        LocalDateTime summerDay = LocalDateTime.of(2016, 7, 31, 14, 15);
+        Assert.assertEquals("31.07.2016 14:15 UTC-04:00", newYorkDateFormatter.format(ZonedDateTime.of(summerDay, ZoneId.of("UTC-4"))));
+    }
+
+    @Test
+    public void shouldPrintFormattedNewYorkZonedDateTime() {
+        String newYorkDateTimePattern = "dd.MM.yyyy HH:mm z";
+        DateTimeFormatter newYorkDateFormatter = DateTimeFormatter.ofPattern(newYorkDateTimePattern);
+        LocalDateTime summerDay = LocalDateTime.of(2016, 7, 31, 14, 15);
+        Assert.assertEquals("31.07.2016 14:15 EDT", newYorkDateFormatter.format(ZonedDateTime.of(summerDay, ZoneId.of("America/New_York"))));
+    }
+
+    @Test
+    public void shouldPrintStyledDate() {
+        LocalDate anotherSummerDay = LocalDate.of(2016, 8, 23);
+        Assert.assertEquals("Tuesday, August 23, 2016", DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL).format(anotherSummerDay));
+        Assert.assertEquals("August 23, 2016", DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG).format(anotherSummerDay));
+        Assert.assertEquals("Aug 23, 2016", DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).format(anotherSummerDay));
+        Assert.assertEquals("8/23/16", DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT).format(anotherSummerDay));
+    }
+
+    @Test
+    public void shouldPrintStyledDateTime() {
+        LocalDateTime anotherSummerDay = LocalDateTime.of(2016, 8, 23, 13, 12, 45);
+        Assert.assertEquals("Tuesday, August 23, 2016 1:12:45 PM EET", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+        Assert.assertEquals("August 23, 2016 1:12:45 PM EET", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+        Assert.assertEquals("Aug 23, 2016 1:12:45 PM", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+        Assert.assertEquals("8/23/16 1:12 PM", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+    }
+
+    @Test
+    public void shouldPrintFormattedDateTimeWithPredefined() {
+        Assert.assertEquals("2018-03-09", DateTimeFormatter.ISO_LOCAL_DATE.format(LocalDate.of(2018, 3, 9)));
+        Assert.assertEquals("2018-03-09-03:00", DateTimeFormatter.ISO_OFFSET_DATE.format(LocalDate.of(2018, 3, 9).atStartOfDay(ZoneId.of("UTC-3"))));
+        Assert.assertEquals("Fri, 9 Mar 2018 00:00:00 -0300", DateTimeFormatter.RFC_1123_DATE_TIME.format(LocalDate.of(2018, 3, 9).atStartOfDay(ZoneId.of("UTC-3"))));
+    }
+
+    @Test
+    public void shouldParseDateTime() {
+        Assert.assertEquals(LocalDate.of(2018, 3, 12), LocalDate.from(DateTimeFormatter.ISO_LOCAL_DATE.parse("2018-03-09")).plusDays(3));
+    }
+
+    @Test
+    public void shouldParseFormatStyleFull() {
+        ZonedDateTime dateTime = ZonedDateTime.from(DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).parse("Tuesday, August 23, 2016 1:12:45 PM EET"));
+        Assert.assertEquals(ZonedDateTime.of(LocalDateTime.of(2016, 8, 23, 22, 12, 45), ZoneId.of("Europe/Bucharest")), dateTime.plusHours(9));
+    }
+
+    @Test
+    public void shouldParseDateWithCustomFormatter() {
+        DateTimeFormatter europeanDateFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy");
+        Assert.assertFalse(LocalDate.from(europeanDateFormatter.parse("15.08.2014")).isLeapYear());
+    }
+
+    @Test
+    public void shouldParseTimeWithCustomFormatter() {
+        DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("hh:mm:ss a");
+        Assert.assertTrue(LocalTime.from(timeFormatter.parse("12:25:30 AM")).isBefore(LocalTime.NOON));
+    }
+
+    @Test
+    public void shouldParseZonedDateTimeWithCustomFormatter() {
+        DateTimeFormatter zonedFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm z");
+        Assert.assertEquals(7200, ZonedDateTime.from(zonedFormatter.parse("31.07.2016 14:15 GMT+02:00")).getOffset().getTotalSeconds());
+    }
+
+    @Test(expected = DateTimeParseException.class)
+    public void shouldExpectAnExceptionIfDateTimeStringNotMatchPattern() {
+        DateTimeFormatter zonedFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm z");
+        ZonedDateTime.from(zonedFormatter.parse("31.07.2016 14:15"));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/FormattedDateMatcherUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.regexp.datepattern;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class FormattedDateMatcherUnitTest {
+
+    private DateMatcher matcher = new FormattedDateMatcher();
+
+    @Test
+    public void whenUsingFormattedDateMatcher_thenFormatConstraintsSatisfied() {
+        Assert.assertTrue(matcher.matches("2017-12-31"));
+        Assert.assertTrue(matcher.matches("2018-01-01"));
+        Assert.assertTrue(matcher.matches("0000-00-00"));
+        Assert.assertTrue(matcher.matches("1029-99-72"));
+
+        Assert.assertFalse(matcher.matches("2018-01"));
+        Assert.assertFalse(matcher.matches("2018-01-01-01"));
+        Assert.assertFalse(matcher.matches("2018-01-XX"));
+        Assert.assertFalse(matcher.matches(" 2018-01-01"));
+        Assert.assertFalse(matcher.matches("2018-01-01 "));
+        Assert.assertFalse(matcher.matches("2018/01/01"));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/RangedDateMatcherUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.regexp.datepattern;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class RangedDateMatcherUnitTest {
+
+    private DateMatcher matcher = new RangedDateMatcher();
+
+    @Test
+    public void whenUsingRangedDateMatcher_thenFormatConstraintsSatisfied() {
+        Assert.assertFalse(matcher.matches("2018-01"));
+        Assert.assertFalse(matcher.matches("2018-01-01-01"));
+        Assert.assertFalse(matcher.matches("2018-01-XX"));
+        Assert.assertFalse(matcher.matches(" 2018-01-01"));
+        Assert.assertFalse(matcher.matches("2018-01-01 "));
+        Assert.assertFalse(matcher.matches("2018/01/01"));
+    }
+
+    @Test
+    public void whenUsingRangedDateMatcher_thenRangeConstraintsSatisfied() {
+        Assert.assertTrue(matcher.matches("1900-01-01"));
+        Assert.assertTrue(matcher.matches("2018-02-31"));
+        Assert.assertTrue(matcher.matches("2999-12-31"));
+
+        Assert.assertFalse(matcher.matches("1899-12-31"));
+        Assert.assertFalse(matcher.matches("2018-05-35"));
+        Assert.assertFalse(matcher.matches("2018-13-05"));
+        Assert.assertFalse(matcher.matches("3000-01-01"));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/gregorian/February29thMatcherUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+import com.baeldung.regexp.datepattern.gregorian.testhelper.GregorianDateTestHelper;
+import org.junit.Test;
+
+public class February29thMatcherUnitTest {
+
+    private DateMatcher matcher = new February29thMatcher();
+
+    private GregorianDateTestHelper testHelper = new GregorianDateTestHelper(matcher);
+
+    @Test
+    public void whenYearIsLeap_thenYearHasFebruary29th() {
+        testHelper.assertFebruary29th();
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/gregorian/FebruaryGeneralMatcherUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+import com.baeldung.regexp.datepattern.gregorian.testhelper.GregorianDateTestHelper;
+import org.junit.Test;
+
+public class FebruaryGeneralMatcherUnitTest {
+
+    private DateMatcher matcher = new FebruaryGeneralMatcher();
+
+    private GregorianDateTestHelper testHelper = new GregorianDateTestHelper(matcher);
+
+    @Test
+    public void whenMonthIsFebruary_thenMonthContainsUpTo28Days() {
+        testHelper.assertFebruaryGeneralDates();
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/gregorian/GregorianDateMatcherUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+import com.baeldung.regexp.datepattern.gregorian.testhelper.GregorianDateTestHelper;
+import org.junit.Test;
+
+public class GregorianDateMatcherUnitTest {
+
+    private DateMatcher matcher = new GregorianDateMatcher();
+
+    private GregorianDateTestHelper testHelper = new GregorianDateTestHelper(matcher);
+
+    @Test
+    public void whenUsingGregorianDateMatcher_thenFormatConstraintsSatisfied() {
+        testHelper.assertFormat();
+    }
+
+    @Test
+    public void whenUsingGregorianDateMatcher_thenRangeConstraintsSatisfied() {
+        testHelper.assertRange();
+    }
+
+    @Test
+    public void whenYearIsLeap_thenFebruaryHas29Days() {
+        testHelper.assertFebruary29th();
+    }
+
+    @Test
+    public void whenMonthIsFebruary_thenMonthContainsUpTo28Days() {
+        testHelper.assertFebruaryGeneralDates();
+    }
+
+    @Test
+    public void whenMonthIsShort_thenMonthContainsUpTo30Days() {
+        testHelper.assertMonthsOf30Days();
+    }
+
+    @Test
+    public void whenMonthIsLong_thenMonthContainsUpTo31Days() {
+        testHelper.assertMonthsOf31Dates();
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/gregorian/MonthsOf30DaysMatcherUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+import com.baeldung.regexp.datepattern.gregorian.testhelper.GregorianDateTestHelper;
+import org.junit.Test;
+
+public class MonthsOf30DaysMatcherUnitTest {
+
+    private DateMatcher matcher = new MonthsOf30DaysMatcher();
+
+    private GregorianDateTestHelper testHelper = new GregorianDateTestHelper(matcher);
+
+    @Test
+    public void whenMonthIsShort_thenMonthContainsUpTo30Days() {
+        testHelper.assertMonthsOf30Days();
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/gregorian/MonthsOf31DaysMatcherUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.regexp.datepattern.gregorian;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+import com.baeldung.regexp.datepattern.gregorian.testhelper.GregorianDateTestHelper;
+import org.junit.Test;
+
+public class MonthsOf31DaysMatcherUnitTest {
+
+    private DateMatcher matcher = new MonthsOf31DaysMatcher();
+
+    private GregorianDateTestHelper testHelper = new GregorianDateTestHelper(matcher);
+
+    @Test
+    public void whenMonthIsLong_thenMonthContainsUpTo31Days() {
+        testHelper.assertMonthsOf31Dates();
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/regexp/datepattern/gregorian/testhelper/GregorianDateTestHelper.java

@@ -0,0 +1,102 @@
+package com.baeldung.regexp.datepattern.gregorian.testhelper;
+
+import com.baeldung.regexp.datepattern.DateMatcher;
+import org.junit.Assert;
+
+public class GregorianDateTestHelper {
+
+    private final DateMatcher matcher;
+
+    public GregorianDateTestHelper(DateMatcher matcher) {
+        this.matcher = matcher;
+    }
+
+    public void assertFormat() {
+        Assert.assertTrue(matcher.matches("2017-12-31"));
+        Assert.assertTrue(matcher.matches("2018-01-01"));
+
+        Assert.assertFalse(matcher.matches("2018-02"));
+        Assert.assertFalse(matcher.matches("2018-02-01-01"));
+        Assert.assertFalse(matcher.matches("2018-02-XX"));
+        Assert.assertFalse(matcher.matches(" 2018-02-01"));
+        Assert.assertFalse(matcher.matches("2018-02-01 "));
+        Assert.assertFalse(matcher.matches("2020/02/28"));
+        Assert.assertFalse(matcher.matches("2020.02.29"));
+    }
+
+    public void assertRange() {
+        Assert.assertTrue(matcher.matches("1900-01-01"));
+        Assert.assertTrue(matcher.matches("2205-05-25"));
+        Assert.assertTrue(matcher.matches("2999-12-31"));
+
+        Assert.assertFalse(matcher.matches("1899-12-31"));
+        Assert.assertFalse(matcher.matches("2018-05-35"));
+        Assert.assertFalse(matcher.matches("2018-13-05"));
+        Assert.assertFalse(matcher.matches("3000-01-01"));
+        Assert.assertFalse(matcher.matches("3200-02-29"));
+    }
+
+    public void assertFebruary29th() {
+        Assert.assertTrue(matcher.matches("2000-02-29"));
+        Assert.assertTrue(matcher.matches("2400-02-29"));
+        Assert.assertTrue(matcher.matches("2800-02-29"));
+        Assert.assertTrue(matcher.matches("2020-02-29"));
+        Assert.assertTrue(matcher.matches("2024-02-29"));
+        Assert.assertTrue(matcher.matches("2028-02-29"));
+
+        Assert.assertFalse(matcher.matches("2017-02-29"));
+        Assert.assertFalse(matcher.matches("2018-02-29"));
+        Assert.assertFalse(matcher.matches("2019-02-29"));
+        Assert.assertFalse(matcher.matches("2100-02-29"));
+        Assert.assertFalse(matcher.matches("2200-02-29"));
+        Assert.assertFalse(matcher.matches("2300-02-29"));
+    }
+
+    public void assertFebruaryGeneralDates() {
+        Assert.assertTrue(matcher.matches("2018-02-01"));
+        Assert.assertTrue(matcher.matches("2019-02-13"));
+        Assert.assertTrue(matcher.matches("2020-02-25"));
+
+        Assert.assertFalse(matcher.matches("2000-02-30"));
+        Assert.assertFalse(matcher.matches("2400-02-62"));
+        Assert.assertFalse(matcher.matches("2420-02-94"));
+    }
+
+    public void assertMonthsOf30Days() {
+        Assert.assertTrue(matcher.matches("2018-04-30"));
+        Assert.assertTrue(matcher.matches("2019-06-30"));
+        Assert.assertTrue(matcher.matches("2020-09-30"));
+        Assert.assertTrue(matcher.matches("2021-11-30"));
+
+        Assert.assertTrue(matcher.matches("2022-04-02"));
+        Assert.assertTrue(matcher.matches("2023-06-14"));
+        Assert.assertTrue(matcher.matches("2024-09-26"));
+
+        Assert.assertFalse(matcher.matches("2018-04-31"));
+        Assert.assertFalse(matcher.matches("2019-06-31"));
+        Assert.assertFalse(matcher.matches("2020-09-31"));
+        Assert.assertFalse(matcher.matches("2021-11-31"));
+
+        Assert.assertFalse(matcher.matches("2022-04-32"));
+        Assert.assertFalse(matcher.matches("2023-06-64"));
+        Assert.assertFalse(matcher.matches("2024-09-96"));
+    }
+
+    public void assertMonthsOf31Dates() {
+        Assert.assertTrue(matcher.matches("2018-01-31"));
+        Assert.assertTrue(matcher.matches("2019-03-31"));
+        Assert.assertTrue(matcher.matches("2020-05-31"));
+        Assert.assertTrue(matcher.matches("2021-07-31"));
+        Assert.assertTrue(matcher.matches("2022-08-31"));
+        Assert.assertTrue(matcher.matches("2023-10-31"));
+        Assert.assertTrue(matcher.matches("2024-12-31"));
+
+        Assert.assertTrue(matcher.matches("2025-01-03"));
+        Assert.assertTrue(matcher.matches("2026-03-15"));
+        Assert.assertTrue(matcher.matches("2027-05-27"));
+
+        Assert.assertFalse(matcher.matches("2018-01-32"));
+        Assert.assertFalse(matcher.matches("2019-03-64"));
+        Assert.assertFalse(matcher.matches("2020-05-96"));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/simpledateformat/SimpleDateFormatUnitTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.simpledateformat;
+
+import org.junit.Test;
+
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
+import java.util.TimeZone;
+import java.util.logging.Logger;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+
+public class SimpleDateFormatUnitTest {
+
+  private static final Logger logger = Logger.getLogger(SimpleDateFormatUnitTest.class.getName());
+
+  @Test
+  public void givenSpecificDate_whenFormatted_thenCheckFormatCorrect() throws Exception {
+    SimpleDateFormat formatter = new SimpleDateFormat("dd-MM-yyyy");
+    assertEquals("24-05-1977", formatter.format(new Date(233345223232L)));
+  }
+
+  @Test
+  public void givenSpecificDate_whenFormattedUsingDateFormat_thenCheckFormatCorrect() throws Exception {
+    DateFormat formatter = DateFormat.getDateInstance(DateFormat.SHORT, Locale.US);
+    assertEquals("5/24/77", formatter.format(new Date(233345223232L)));
+  }
+
+  @Test
+  public void givenStringDate_whenParsed_thenCheckDateCorrect() throws Exception{
+    SimpleDateFormat formatter = new SimpleDateFormat("dd-MM-yyyy");
+    formatter.setTimeZone(TimeZone.getTimeZone("Europe/London"));
+    Date myDate = new Date(233276400000L);
+    Date parsedDate = formatter.parse("24-05-1977");
+    assertEquals(myDate.getTime(), parsedDate.getTime());
+  }
+
+  @Test
+  public void givenFranceLocale_whenFormatted_thenCheckFormatCorrect() throws Exception{
+    SimpleDateFormat franceDateFormatter = new SimpleDateFormat("EEEEE dd-MMMMMMM-yyyy", Locale.FRANCE);
+    Date myWednesday = new Date(1539341312904L);
+    assertTrue(franceDateFormatter.format(myWednesday).startsWith("vendredi"));
+  }
+
+  @Test
+  public void given2TimeZones_whenFormatted_thenCheckTimeDifference() throws Exception {
+    Date now = new Date();
+
+    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EEEE dd-MMM-yy HH:mm:ssZ");
+
+    simpleDateFormat.setTimeZone(TimeZone.getTimeZone("Europe/London"));
+    logger.info(simpleDateFormat.format(now));
+    //change the date format
+    simpleDateFormat.setTimeZone(TimeZone.getTimeZone("America/New_York"));
+    logger.info(simpleDateFormat.format(now));
+  }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/timestamp/StringToTimestampConverterUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.timestamp;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.sql.Timestamp;
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+
+public class StringToTimestampConverterUnitTest {
+
+    @Test
+    public void givenDatePattern_whenParsing_thenTimestampIsCorrect() {
+        String pattern = "MMM dd, yyyy HH:mm:ss.SSSSSSSS";
+        String timestampAsString = "Nov 12, 2018 13:02:56.12345678";
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
+        LocalDateTime localDateTime = LocalDateTime.from(formatter.parse(timestampAsString));
+
+        Timestamp timestamp = Timestamp.valueOf(localDateTime);
+        Assert.assertEquals("2018-11-12 13:02:56.12345678", timestamp.toString());
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/timestamp/TimestampToStringConverterTest.java

@@ -0,0 +1,19 @@
+package com.baeldung.timestamp;
+
+import org.junit.Assert;
+import org.junit.jupiter.api.Test;
+
+import java.sql.Timestamp;
+import java.time.format.DateTimeFormatter;
+
+public class TimestampToStringConverterTest {
+
+    @Test
+    public void givenDatePattern_whenFormatting_thenResultingStringIsCorrect() {
+        Timestamp timestamp = Timestamp.valueOf("2018-12-12 01:02:03.123456789");
+        DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
+
+        String timestampAsString = formatter.format(timestamp.toLocalDateTime());
+        Assert.assertEquals("2018-12-12T01:02:03.123456789", timestampAsString);
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/zonedatetime/OffsetDateTimeExampleUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.zonedatetime;
+
+import static org.junit.Assert.assertTrue;
+
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+
+import org.junit.Test;
+
+public class OffsetDateTimeExampleUnitTest {
+
+    OffsetDateTimeExample offsetDateTimeExample = new OffsetDateTimeExample();
+
+    @Test
+    public void givenZoneOffset_whenGetCurrentTime_thenResultHasZone() {
+        String offset = "+02:00";
+        OffsetDateTime time = offsetDateTimeExample.getCurrentTimeByZoneOffset(offset);
+
+        assertTrue(time.getOffset()
+            .equals(ZoneOffset.of(offset)));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/zonedatetime/OffsetTimeExampleUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.zonedatetime;
+
+import static org.junit.Assert.assertTrue;
+
+import java.time.OffsetTime;
+import java.time.ZoneOffset;
+
+import org.junit.Test;
+
+public class OffsetTimeExampleUnitTest {
+
+    OffsetTimeExample offsetTimeExample = new OffsetTimeExample();
+
+    @Test
+    public void givenZoneOffset_whenGetCurrentTime_thenResultHasZone() {
+        String offset = "+02:00";
+        OffsetTime time = offsetTimeExample.getCurrentTimeByZoneOffset(offset);
+
+        assertTrue(time.getOffset()
+            .equals(ZoneOffset.of(offset)));
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/zonedatetime/ZoneDateTimeExampleUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.zonedatetime;
+
+import static org.junit.Assert.assertTrue;
+
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+
+import org.junit.Test;
+
+public class ZoneDateTimeExampleUnitTest {
+
+    ZoneDateTimeExample zoneDateTimeExample = new ZoneDateTimeExample();
+
+    @Test
+    public void givenZone_whenGetCurrentTime_thenResultHasZone() {
+        String zone = "Europe/Berlin";
+        ZonedDateTime time = zoneDateTimeExample.getCurrentTimeByZoneId(zone);
+
+        assertTrue(time.getZone()
+            .equals(ZoneId.of(zone)));
+    }
+
+    @Test
+    public void givenZones_whenConvertDateByZone_thenGetConstantDiff() {
+        String sourceZone = "Europe/Berlin";
+        String destZone = "Asia/Tokyo";
+        ZonedDateTime sourceDate = zoneDateTimeExample.getCurrentTimeByZoneId(sourceZone);
+        ZonedDateTime destDate = zoneDateTimeExample.convertZonedDateTime(sourceDate, destZone);
+        
+        assertTrue(sourceDate.toInstant()
+            .compareTo(destDate.toInstant()) == 0);
+    }
+}

core-java-modules/core-java-datetime-string/src/test/java/com/baeldung/zonedatetime/ZonedDateTimeUnitTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.zonedatetime;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.util.logging.Logger;
+
+import org.junit.jupiter.api.Test;
+
+public class ZonedDateTimeUnitTest {
+
+    private static final Logger log = Logger.getLogger(ZonedDateTimeUnitTest.class.getName());
+
+    @Test
+    public void givenZonedDateTime_whenConvertToString_thenOk() {
+
+        ZonedDateTime zonedDateTimeNow = ZonedDateTime.now(ZoneId.of("UTC"));
+        ZonedDateTime zonedDateTimeOf = ZonedDateTime.of(2018, 01, 01, 0, 0, 0, 0, ZoneId.of("UTC"));
+
+        LocalDateTime localDateTime = LocalDateTime.now();
+        ZonedDateTime zonedDateTime = ZonedDateTime.of(localDateTime, ZoneId.of("UTC"));
+
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM/dd/yyyy - HH:mm:ss Z");
+        String formattedString = zonedDateTime.format(formatter);
+
+        DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("MM/dd/yyyy - HH:mm:ss z");
+        String formattedString2 = zonedDateTime.format(formatter2);
+
+        log.info(formattedString);
+        log.info(formattedString2);
+
+    }
+
+    @Test
+    public void givenString_whenParseZonedDateTime_thenOk() {
+        ZonedDateTime zonedDateTime = ZonedDateTime.parse("2011-12-03T10:15:30+01:00");
+
+        log.info(zonedDateTime.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));
+    }
+    
+    @Test
+    public void givenString_whenParseZonedDateTimeWithoutZone_thenException() {
+        assertThrows(DateTimeParseException.class, () -> ZonedDateTime.parse("2011-12-03T10:15:30", DateTimeFormatter.ISO_DATE_TIME));
+    }
+    
+    @Test
+    public void givenString_whenParseLocalDateTimeAtZone_thenOk() {
+        ZoneId timeZone = ZoneId.systemDefault();
+        ZonedDateTime zonedDateTime = LocalDateTime.parse("2011-12-03T10:15:30", DateTimeFormatter.ISO_DATE_TIME).atZone(timeZone);
+
+        log.info(zonedDateTime.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));
+    }
+
+}