How to Correctly Convert a Calendar Date to 'yyyy-MM-dd' Format in Java?

Convert Calendar Date to "yyyy-MM-dd" Format in Java

In Java, converting a calendar date to the "yyyy-MM-dd" format is an essential task for various applications.

Incorrect Approach:

Using the SimpleDateFormat class with the "yyyy-MM-dd" pattern on a Date object obtained from a Calendar may not always yield the desired result. For instance, the following code snippet will produce "Wed Sep 26 00:00:00 IST 2012" instead of "2012-09-26":

Calendar cal = Calendar.getInstance();
cal.add(Calendar.DATE, 1);
Date date = cal.getTime();             
SimpleDateFormat format1 = new SimpleDateFormat("yyyy-MM-dd");
String date1 = format1.format(date);  

Correct Approach:

To convert a calendar date to the "yyyy-MM-dd" format correctly, you need to understand the difference between a Date and a LocalDateTime.

Java 8 :

In Java 8 and later, you can use the LocalDateTime class, which represents a date and time without a time zone.

LocalDateTime ldt = LocalDateTime.now().plusDays(1);
DateTimeFormatter formmat1 = DateTimeFormatter.ofPattern("yyyy-MM-dd", Locale.ENGLISH);
String formatter = formmat1.format(ldt);
System.out.println(formatter);

Prior to Java 8:

If you're using Java versions prior to 8, you should consider using the ThreeTen Backport library.

Calendar cal = Calendar.getInstance();
cal.add(Calendar.DATE, 1);
SimpleDateFormat format1 = new SimpleDateFormat("yyyy-MM-dd");
String formatted = format1.format(cal.getTime());

Remember, while the above code initially produces the desired string "2012-09-26," parsing it back into a Date will result in "Wed Sep 26 00:00:00 EST 2012." This is because Date represents the number of milliseconds since a fixed point in time, and formatting it only modifies its string representation.

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