Convert String “1/1/1970” to a date object formatted as “19700101000000”?

Question

I am writing Junit tests to verify data entered after it has been transformed into a different format. How would I convert a String like "1/1/1970" into a date object formatted like 19700101000000? I tried this:

DateFormat format = new SimpleDateFormat("yyyyMMddHHmmss");
Date date = format.parse("1/1/1970");

But "1/1/1970" throws an Unparseable date ParseException. Thanks!

Answer 1

You must use different DateFormat s to parse and to format. Right now you're taking "1/1/1970" and trying to read it with the date format "yyyyMMddHHmmss". You'll need to parse with the format MM/dd/yyyy , get out a Date , and then format it with your format "yyyyMMddHHmmss".

Answer 2

You need to parse using one formatter, then reformat using another. Here's code for old style, and for new java.time API built into Java 8 and later.

String input = "1/1/1970";

// Using SimpleDateFormat
Date date = new SimpleDateFormat("M/d/yyyy").parse(input);
System.out.println(new SimpleDateFormat("yyyyMMddHHmmss").format(date));

// Using Java 8 java.time
LocalDate localDate = LocalDate.parse(input, DateTimeFormatter.ofPattern("M/d/uuuu"));
System.out.println(localDate.atStartOfDay().format(DateTimeFormatter.ofPattern("uuuuMMddHHmmss")));

Answer 3

As Louis Wasserman indicated, format.parse the input date String to a Date object. Then use that Date object as input to another SimpleDateFormat object.

Something like this :

public class DateFormatTest {

public static void main(String[] args) {
    String inputDate = args[0];
    java.util.Date d = null;
    java.text.DateFormat inputDateFormat = new java.text.SimpleDateFormat("MM/dd/yyyy");
    java.text.DateFormat outputDateFormat = new java.text.SimpleDateFormat("yyyyMMddHHmmss");
    try {
        d = inputDateFormat.parse(intputDate);
    } catch (java.text.ParseException ex) {
        System.err.println("something horrible went wrong!");
    }
    String output = outputDateFormat.format(d);
    System.out.println("The input date of: " + inputDate + " was re-formatted to: " + output);
  }
}

Providing "1/1/1970" as the input parameter, the output is:

The input date of: 1/1/1970 was re-formatted to: 19700101000000