Java String to Date object of the format “MM/dd/yyyy HH:mm:ss a”

Question

I need to convert a String containing a date into a date object.

The String will be in the format "yyyy-mm-dd HH:mm:ss" and I want the "MM/dd/yyyy HH:mm:ss a " format as result.

String dateString = "2018-03-20 09:31:31";

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM/dd/yyyy HH:mm:ss a", 
                                                           Locale.ENGLISH);

LocalDate date = LocalDate.parse(dateString , formatter);

The code above is throwing an exception.

Answer 1

You have to use two Formatter, one to covert String to LocalDateTime and the other to format this date as you want :

From String to LocalDateTime :

String dateString = "2018-03-20 09:31:31";

LocalDateTime date = LocalDateTime.parse(
        dateString,
        DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss", Locale.ENGLISH)
);

Now From LocalDateTime to String :

DateTimeFormatter formatter = DateTimeFormatter.ofPattern(
        "MM/dd/yyyy HH:mm:ss a", Locale.ENGLISH
);

String newDate = date.format(formatter);
System.out.println(newDate);// 03/20/2018 09:31:31 AM

---

Note : You have to use LocalDateTime instead of just LocalDate, your format contain both date and time, not just date, else you will get an error :

java.time.temporal.UnsupportedTemporalTypeException: Unsupported field: HourOfDay

Answer 2

That's a common error, based on the misconception that dates have formats - but they actually don't.

Date/time objects have only values, and those values - usually numerical - represent the concept of a date (a specific point in the calendar) and a time (a specific moment of the day).

If you have a String, then you don't actually have a date. You have a text (a sequence of characters) that represents a date. Note that all of the strings below are different (they have a different sequence of characters), but all represent the same date (the same values, the same point in the calendar):

• 2018-03-20 09:31:31
• 03/20/2018 9:31:31 AM (using USA's format: month/day/year)
• Tuesday, March 20th 2018, 09:31:31 am
• and many others...

What you want to do is to get one format (one String, one text representing a date) and transform it to another format (anoter String, another different sequence of characters that represents the same date).

In Java (and in many other languages - if not all - btw) you must do it in 2 steps:

1. convert the String to a date/time object (convert the text to the numerical values) - that's what the parse method does
2. convert the date/time object to another format (convert the numerical values to another text)

That said, when you call the parse method, you're trying to transform a String (a text, a sequence of characters) into a date/time object. This means that the DateTimeFormatter must have a pattern that matches the input.

The input is 2018-03-20 09:31:31, which is year-month-day hour:minute:second. And the formatter you used to parse it has the pattern MM/dd/yyyy HH:mm:ss a (month/day/year hour:minute:second am/pm).

You used the output pattern (the one that should be used in step 2) to parse the input. That's why you've got an exception: the formatter tried to parse a month with 2 digits followed by a / when the input actually contains a year with 4 digits followed by a -.

You must use a different DateTimeFormatter for each step, using the correct pattern for each case. YCF_L's answer has the code that does the job, I'd just like to add one little detail. The formatter used for the output (step 2) is:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern(
        "MM/dd/yyyy HH:mm:ss a", Locale.ENGLISH
);

Note that HH is used for the hours. Take a look at the javadoc and you'll see that uppercase HH represents the hour-of-day fields (values from 0 to 23 - so 1 AM is printed as 01 and 1 PM is printed as 13).

But you're also printing the AM/PM field (the a in the pattern), so maybe what you need is actually the lowercase hh, which is the clock-hour-of-am-pm (values from 1 to 12) or even KK (hour-of-am-pm (values from 0 to 11)).