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Java 8 – Format Date, LocalDate, LocalDateTime and ZonedDateTime
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‎java8-examples/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.howtoprogram</groupId>
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<artifactId>java8-examples</artifactId>
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<version>1.0-SNAPSHOT</version>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<java.version>1.8</java.version>
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<junit.version>4.12</junit.version>
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</properties>
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<build>
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<plugins>
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<plugin>
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<artifactId>maven-compiler-plugin</artifactId>
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<version>3.1</version>
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<configuration>
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<source>${java.version}</source>
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<target>${java.version}</target>
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</configuration>
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</plugin>
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</plugins>
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</build>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>${junit.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎java8-examples/src/test/java/Java8DateTimeTest.java

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import org.junit.Test;
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import java.time.Instant;
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import java.time.LocalDate;
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import java.time.LocalDateTime;
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import java.time.ZoneId;
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import java.util.Calendar;
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import java.util.Date;
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import java.util.GregorianCalendar;
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import static org.junit.Assert.assertEquals;
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public class Java8DateTimeTest {
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@Test
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public void testConvertLocalDateToDate() {
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LocalDate localDate = LocalDate.of(2017, 8, 10);
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Date date = Date.from(localDate.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant());
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Calendar calendar = Calendar.getInstance();
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calendar.setTime(date);
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assertEquals(localDate.getYear(), calendar.get(Calendar.YEAR));
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assertEquals(localDate.getMonth().getValue(), calendar.get(Calendar.MONTH) + 1);
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assertEquals(localDate.getDayOfMonth(), calendar.get(Calendar.DAY_OF_MONTH));
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}
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@Test
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public void testConvertLocalDateTimeToDate() {
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LocalDateTime localDateTime = LocalDateTime.of(2017, 8, 10, 23, 10, 15);
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Date date = Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
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Calendar calendar = Calendar.getInstance();
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calendar.setTime(date);
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assertEquals(localDateTime.getYear(), calendar.get(Calendar.YEAR));
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assertEquals(localDateTime.getMonth().getValue(), calendar.get(Calendar.MONTH) + 1);
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assertEquals(localDateTime.getDayOfMonth(), calendar.get(Calendar.DAY_OF_MONTH));
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}
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@Test
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public void testConvertDateToLocalDate() {
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Calendar calendar = new GregorianCalendar(2017, Calendar.AUGUST, 20);
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Date date = calendar.getTime();
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//Convert Date to LocalDate
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LocalDate localDate = Instant.ofEpochMilli(date.getTime()).atZone(
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ZoneId.systemDefault()).toLocalDate();
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assertEquals(calendar.get(Calendar.YEAR), localDate.getYear());
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assertEquals(calendar.get(Calendar.MONTH) + 1, localDate.getMonth()
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.getValue());
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assertEquals(calendar.get(Calendar.DAY_OF_MONTH), localDate.getDayOfMonth());
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}
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@Test
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public void testConvertDateToLocalDateTime() {
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Calendar calendar = new GregorianCalendar(2017, Calendar.AUGUST, 20);
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Date date = calendar.getTime();
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//Convert Date to LocalDateTime
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LocalDateTime localDateTime = Instant.ofEpochMilli(date.getTime()).atZone(ZoneId
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.systemDefault()).toLocalDateTime();
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assertEquals(calendar.get(Calendar.YEAR), localDateTime.getYear());
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assertEquals(calendar.get(Calendar.MONTH) + 1, localDateTime.getMonth()
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.getValue());
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assertEquals(calendar.get(Calendar.DAY_OF_MONTH), localDateTime.getDayOfMonth());
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assertEquals(calendar.get(Calendar.HOUR_OF_DAY), localDateTime.getHour());
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assertEquals(calendar.get(Calendar.MINUTE), localDateTime.getMinute());
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assertEquals(calendar.get(Calendar.SECOND), localDateTime.getSecond());
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}
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}

‎java8-examples/src/test/java/Java8FormatDate.java

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import org.junit.Test;
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import java.text.SimpleDateFormat;
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import java.time.*;
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import java.time.format.DateTimeFormatter;
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import java.util.Calendar;
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import java.util.Date;
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import java.util.GregorianCalendar;
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import java.util.Locale;
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import static java.time.format.DateTimeFormatter.*;
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import static org.junit.Assert.assertEquals;
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public class Java8FormatDate {
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@Test
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public void testFormatDate() {
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//create a date object by using Calendar
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Calendar calendar = new GregorianCalendar(2020, Calendar.AUGUST, 9);
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Date date = calendar.getTime();
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//create a pattern
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String pattern = "dd/MM/yyyy";
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SimpleDateFormat dateFormatter = new SimpleDateFormat(pattern);
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// format the date
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String olympicDate = dateFormatter.format(date);
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//Validate
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assertEquals("09/08/2020", olympicDate);
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}
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@Test
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public void testFormatDateLongPattern() {
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//create a date
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int year = 2020;
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int month = Calendar.AUGUST;
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int day = 9;
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int hourOfDay = 23;
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int minute = 59;
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int second = 59;
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Calendar calendar = new GregorianCalendar(year, month, day, hourOfDay,
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minute, second);
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Date date = calendar.getTime();
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//create a long pattern with en_US locale
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String pattern = "EEEEE MMMMM yyyy HH:mm:ss.SSS";
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SimpleDateFormat dateFormatter =
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new SimpleDateFormat(pattern, new Locale("en", "US"));
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//format the date
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String olympicDate = dateFormatter.format(date);
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//validate
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assertEquals("Sunday August 2020 23:59:59.000", olympicDate);
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}
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@Test
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public void testFormatLocalDate() {
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//create a LocalDate object
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LocalDate date = LocalDate.of(2020, Month.AUGUST, 9);
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//create a pattern
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String pattern = "dd/MM/yyyy";
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DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
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// format the date
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String olympicDate = formatter.format(date);
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//Validate
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assertEquals("09/08/2020", olympicDate);
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}
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@Test
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public void testFormatLocalDateUsingPreDefinedFormatter() {
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//create a LocalDate object
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LocalDate date = LocalDate.of(2020, Month.AUGUST, 9);
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// format the date
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String olympicDate = ISO_DATE.format(date);
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assertEquals("2020-08-09", olympicDate);
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//or use as a pattern
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olympicDate = date.format(ISO_DATE);
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assertEquals("2020-08-09", olympicDate);
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}
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@Test
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public void testFormatLocalDateTime() {
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//create a LocalDate object
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LocalDateTime dt = LocalDateTime.of(2020, Month.AUGUST, 9, 23, 59, 59);
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//create a pattern
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String pattern = "yyyy/MM/dd HH:mm:ss";
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DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
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// format the date
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String olympicDate = formatter.format(dt);
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assertEquals("2020/08/09 23:59:59", olympicDate);
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}
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@Test
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public void testFormatLocalDateTimeUsingPreDefinedFormatters() {
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//create a LocalDate object
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LocalDateTime dt = LocalDateTime.of(2020, Month.AUGUST, 9, 23, 59, 59);
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// format the date
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String olympicDate = ISO_LOCAL_DATE_TIME.format(dt);
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assertEquals("2020-08-09T23:59:59", olympicDate);
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// or using as a pattern
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olympicDate = dt.format(ISO_LOCAL_DATE_TIME);
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assertEquals("2020-08-09T23:59:59", olympicDate);
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}
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@Test
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public void testFormatZonedDateTime() {
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//create a LocalDate object
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LocalDateTime dt = LocalDateTime.of(2020, Month.AUGUST, 9, 23, 59, 59);
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ZonedDateTime japanZonedDT = ZonedDateTime.of(dt, ZoneId.of("Asia/Tokyo"));
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// format the date
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String pattern = "yyyy/MM/dd HH:mm:ssXXX";
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DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
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String olympicDate = formatter.format(japanZonedDT);
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assertEquals("2020/08/09 23:59:59+09:00", olympicDate);
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}
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@Test
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public void testFormatZonedDateTimeUsingPreDefinedFormatters() {
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//create a LocalDate object
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LocalDateTime dt = LocalDateTime.of(2020, Month.AUGUST, 9, 23, 59, 59);
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ZonedDateTime japanZonedDT = ZonedDateTime.of(dt, ZoneId.of("Asia/Tokyo"));
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// format the date
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String olympicDate = ISO_OFFSET_DATE_TIME.format(japanZonedDT);
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assertEquals("2020-08-09T23:59:59+09:00", olympicDate);
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// or using as a pattern
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olympicDate = japanZonedDT.format(ISO_OFFSET_DATE_TIME);
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assertEquals("2020-08-09T23:59:59+09:00", olympicDate);
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}
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}

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