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how to print DateTime value

I have this code and I want to print out the time as String without the 'T' character between date and time.
String datetime4 =new StringBuilder().append(date4).append(time4).toString();
DateTime newdt=new DateTime(datetime4);
DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd'T'HH:mm:ss");
newdt = formatter.parseDateTime(datetime4);
System.out.println(newdt);
Notice that date4 and time4 are String variables.
It will print:
2017-11-04T11:23:00.000+02:00

One way of doing it:
String date4 = "2017-02-02";
String time4 = "12:00:00";
//To parse it to Temporal object
DateTime dateTime = DateTime.parse(date4 +"T"+ time4);
// to output it as String in a prefered format (Thanks #Hugo)
System.out.println(dateTime.toString("yyyy-MM-dd HH:mm:ss"));
If you prefer Java 8 you will need to use formatter I think, LocalDateTime doesn't overload toString in the same way as JodaTime.
But not sure why you want to do this? seems like just appending both date and time is enough? Anyway if you want to parse to the date you need to put T as is needed to pass it as a valid date time format to DateTime as well as LocalDateTime if using Java8, then you can reformat it as you wish.
String date4 = "2017-02-02";
String time4 = "12:00:00";
LocalDateTime dateTime = LocalDateTime.parse(date4 +"T"+ time4);
System.out.println(dateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));

Using Java 8 LocalDateTime;
LocalDateTime dateTime;
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mm:ss");
DateTimeFormatter desiredFormat = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss");
dateTime = LocalDateTime.parse("2017-06-01T12:10:10", formatter);
System.out.println(desiredFormat.format(dateTime));

When you do:
System.out.println(newdt);
You're printing the newdt variable, and internally println calls the toString() method on the object.
As this variable's type is DateTime, this code outputs the result of newdt.toString(). And Datetime.toString() method uses a default format that contains the "T".
If you want the output String to have a different format, you can do something like this:
System.out.println(newdt.toString("yyyy-MM-dd HH:mm:ss"));
The output will be:
2017-11-04 11:23:00
(without the "T")
You can use this version of toString with any pattern accepted by DateTimeFormatter.
You can also create another DateTimeFormatter for the format you want:
DateTimeFormatter withoutT = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss");
System.out.println(withoutT.print(newdt));
The output will be the same, it's up to you to choose.

How can I create a Java 8 LocalDate from a long Epoch time in Milliseconds?

I have an external API that returns me dates as longs, represented as milliseconds since the beginning of the Epoch.
With the old style Java API, I would simply construct a Date from it with
Date myDate = new Date(startDateLong)
What is the equivalent in Java 8's LocalDate/LocalDateTime classes?
I am interested in converting the point in time represented by the long to a LocalDate in my current local timezone.

If you have the milliseconds since the Epoch and want to convert them to a local date using the current local timezone, you can use Instant.ofEpochMilli(long epochMilli)
LocalDate date =
Instant.ofEpochMilli(longValue).atZone(ZoneId.systemDefault()).toLocalDate();
but keep in mind that even the system’s default time zone may change, thus the same long value may produce different result in subsequent runs, even on the same machine.
Further, keep in mind that LocalDate, unlike java.util.Date, really represents a date, not a date and time.
Otherwise, you may use a LocalDateTime:
LocalDateTime date =
LocalDateTime.ofInstant(Instant.ofEpochMilli(longValue), ZoneId.systemDefault());

You can start with Instant.ofEpochMilli(long):
LocalDate date =
Instant.ofEpochMilli(startDateLong)
.atZone(ZoneId.systemDefault())
.toLocalDate();

I think I have a better answer.
new Timestamp(longEpochTime).toLocalDateTime();

Timezones and stuff aside, a very simple alternative to new Date(startDateLong) could be LocalDate.ofEpochDay(startDateLong / 86400000L)

A simple version based on #Michael Piefel answer:
LocalDate myDate = LocalDate.ofEpochDay(Duration.ofMillis(epochMillis).toDays());

replace now.getTime() with your long value.
//GET UTC time for current date
Date now= new Date();
//LocalDateTime utcDateTimeForCurrentDateTime = Instant.ofEpochMilli(now.getTime()).atZone(ZoneId.of("UTC")).toLocalDateTime();
LocalDate localDate = Instant.ofEpochMilli(now.getTime()).atZone(ZoneId.of("UTC")).toLocalDate();
DateTimeFormatter dTF2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
System.out.println(" formats as " + dTF2.format(utcDateTimeForCurrentDateTime));

I have tested this alternative solution for LocalDateTime:
public static LocalDateTime increaseByMillis(final LocalDateTime ldt, final long millis)
{
return LocalDateTime.ofInstant(Instant.ofEpochMilli(ldt.toInstant(ZoneOffset.UTC).toEpochMilli()+millis), ZoneId.of(ZoneOffset.UTC.getId()));
}
Test:
LocalDateTime test = LocalDateTime.now();
LocalDateTime increased = MyUtilsAbc.increaseByMillis(test, 1000);
Assert.assertEquals("Increase of LocalDateTime not working (anymore)!", test.toEpochSecond(ZoneOffset.UTC) +1, increased.toEpochSecond(ZoneOffset.UTC));

In a specific case where your epoch seconds timestamp comes from SQL or is related to SQL somehow, you can obtain it like this:
long startDateLong = <...>
LocalDate theDate = new java.sql.Date(startDateLong).toLocalDate();

How to Convert String to LocalDateTime?

I have a string "2015-09-17T12:00". How can I convert this String to LocalDateTime in format "yyyy-MM-dd HH:mm" and then convert it back to String?

you can Replace T with whitespace(s):
String str="2015-09-17T12:00";
str.replace("T"," ");
afterwards convert to Date using SimpleDateFormat;

We can go with DateTimeFormatter, its thread safety.
Refer to below url:
https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html
sample program on converting String to Local Date Time
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd 'T' HH:mm");
LocalDateTime localDateTime = LocalDateTime.parse("2019-18-04 T 18:51", formatter);
Local Date time provides lot of method to get the hours or minutes or seconds
https://docs.oracle.com/javase/8/docs/api/java/time/LocalDateTime.html

Create LocalDate Object from Integers

If I already have a date's month, day, and year as integers, what's the best way to use them to create a LocalDate object? I found this post String to LocalDate , but it starts with a String representation of the date.

Use LocalDate#of(int, int, int) method that takes year, month and dayOfMonth.

You can create LocalDate like this, using ints
LocalDate inputDate = LocalDate.of(year,month,dayOfMonth);
and to create LocalDate from String you can use
String date = "04/04/2004";
inputDate = LocalDate.parse(date,
DateTimeFormat.forPattern("dd/MM/yyyy"));
You can use other formats too but you have to change String in forPattern(...)

In addition to Rohit's answer you can use this code to get Localdate from String
String str = "2015-03-15";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
LocalDate dateTime = LocalDate.parse(str, formatter);
System.out.println(dateTime);

Unable to obtain LocalDateTime from TemporalAccessor when parsing LocalDateTime (Java 8)

I am simply trying to convert a date string into a DateTime object in Java 8. Upon running the following lines:
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMdd");
LocalDateTime dt = LocalDateTime.parse("20140218", formatter);
I get the following error:
Exception in thread "main" java.time.format.DateTimeParseException:
Text '20140218' could not be parsed:
Unable to obtain LocalDateTime from TemporalAccessor:
{},ISO resolved to 2014-02-18 of type java.time.format.Parsed
at java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:1918)
at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1853)
at java.time.LocalDateTime.parse(LocalDateTime.java:492)
The syntax is identical to what has been suggested here, yet I am served with an exception. I am using JDK-8u25.

It turns out Java does not accept a bare Date value as DateTime. Using LocalDate instead of LocalDateTime solves the issue:
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMdd");
LocalDate dt = LocalDate.parse("20140218", formatter);

If you really need to transform a date to a LocalDateTime object, you could use the LocalDate.atStartOfDay(). This will give you a LocalDateTime object at the specified date, having the hour, minute and second fields set to 0:
final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMdd");
LocalDateTime time = LocalDate.parse("20140218", formatter).atStartOfDay();

For what is worth if anyone should read again this topic(like me) the correct answer would be in DateTimeFormatter definition, e.g.:
private static DateTimeFormatter DATE_FORMAT =
new DateTimeFormatterBuilder().appendPattern("dd/MM/yyyy[ [HH][:mm][:ss][.SSS]]")
.parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
.parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
.parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
.toFormatter();
One should set the optional fields if they will appear. And the rest of code should be exactly the same.
Edit : usefull thing from wittyameta comment :
Remember to add the parseDefaulting AFTER you have called appendPattern. Otherwise it'll give DateTimeParseException

For anyone who landed here with this error, like I did:
Unable to obtain LocalDateTime from TemporalAccessor: {HourOfAmPm=0, MinuteOfHour=0}
It came from a the following line:
LocalDateTime.parse(date, DateTimeFormatter.ofPattern("M/d/yy h:mm"));
It turned out that it was because I was using a 12hr Hour pattern on a 0 hour, instead of a 24hr pattern.
Changing the hour to 24hr pattern by using a capital H fixes it:
LocalDateTime.parse(date, DateTimeFormatter.ofPattern("M/d/yy H:mm"));

This is a really unclear and unhelpful error message. After much trial and error I found that LocalDateTime will give the above error if you do not attempt to parse a time. By using LocalDate instead, it works without erroring.
This is poorly documented and the related exception is very unhelpful.

Expanding on retrography's answer..: I had this same problem even when using LocalDate and not LocalDateTime. The issue was that I had created my DateTimeFormatter using .withResolverStyle(ResolverStyle.STRICT);, so I had to use date pattern uuuuMMdd instead of yyyyMMdd (i.e. "year" instead of "year-of-era")!
DateTimeFormatter formatter = new DateTimeFormatterBuilder()
.parseStrict()
.appendPattern("uuuuMMdd")
.toFormatter()
.withResolverStyle(ResolverStyle.STRICT);
LocalDate dt = LocalDate.parse("20140218", formatter);
(This solution was originally a comment to retrography's answer, but I was encouraged to post it as a stand-alone answer because it apparently works really well for many people.)

If the date String does not include any value for hours, minutes and etc you cannot directly convert this to a LocalDateTime. You can only convert it to a LocalDate, because the string only represent the year,month and date components it would be the correct thing to do.
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMdd");
LocalDate ld = LocalDate.parse("20180306", dtf); // 2018-03-06
Anyway you can convert this to LocalDateTime.
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMdd");
LocalDate ld = LocalDate.parse("20180306", dtf);
LocalDateTime ldt = LocalDateTime.of(ld, LocalTime.of(0,0)); // 2018-03-06T00:00

You do not need to define a DateTimeFormatter
You do not need to define a DateTimeFormatter to parse the given date string. You can use the OOTB (Out-Of-The-Box), DateTimeFormatter.BASIC_ISO_DATE to parse it.
Demo:
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
public class Main {
public static void main(String[] args) {
LocalDate date = LocalDate.parse("20140218", DateTimeFormatter.BASIC_ISO_DATE);
System.out.println(date);
// In case you need an instance of LocalDateTime
LocalDateTime ldt = date.atTime(LocalTime.MIN);
System.out.println(ldt);
}
}
Output:
2014-02-18
2014-02-18T00:00
ONLINE DEMO
Learn more about the modern Date-Time API* from Trail: Date Time.
* If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring. Note that Android 8.0 Oreo already provides support for java.time. Check this answer and this answer to learn how to use java.time API with JDBC.

DateTimeFormatter format = new DateTimeFormatterBuilder()
.appendPattern("yyyy-MM-dd")
.parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
.parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
.parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
.parseDefaulting(ChronoField.MILLI_OF_SECOND, 0)
.toFormatter();
Works for me

In cases where you simply want to take a format (whether or not it has time) and want to parse to a LocalDateTime, you can do the following.
LocalDateTime parseDateTime(String dateTime, DateTimeFormatter fmt) {
return fmt.parse(dateTime, t -> {
LocalDate date = t.query(TemporalQueries.localDate());
LocalTime time = t.query(TemporalQueries.localTime());
return LocalDateTime.of(date, time != null ? time : LocalTime.MIDNIGHT);
});
}
I needed this because I was getting the date/time pattern as a parameter for a custom Spark UDF.

This works fine
public class DateDemo {
public static void main(String[] args) {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy hh:mm");
String date = "16-08-2018 12:10";
LocalDate localDate = LocalDate.parse(date, formatter);
System.out.println("VALUE="+localDate);
DateTimeFormatter formatter1 = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm");
LocalDateTime parse = LocalDateTime.parse(date, formatter1);
System.out.println("VALUE1="+parse);
}
}
output:
VALUE=2018-08-16
VALUE1=2018-08-16T12:10

Try this one:
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("MM-dd-yyyy");
LocalDate fromLocalDate = LocalDate.parse(fromdstrong textate, dateTimeFormatter);
You can add any format you want. That works for me!

I arrived at this problem because my input string didn't have a year in it:
input string: Tuesday, June 8 at 10:00 PM
formatter: DateTimeFormatter.ofPattern("EEEE, MMMM d 'at' h:mm a", Locale.US);
I knew the year so I just appended it to get:
input string: Tuesday, June 8 at 6:30 PM 2021
formatter: DateTimeFormatter.ofPattern("EEEE, MMMM d 'at' h:mm a uuuu", Locale.US);