Toufik Toufik - 1 year ago 73
HTML Question

SimpleDateFormat doesn't give me the pattern I need

I'm having a problem with SimpleDateFormat. I have inputfields in my HTML-page with type = date. I want to save these values into my database where they should be saved as dates. I already figured out how to do this and it works. The only probem I encouter is the way the dates are represented in the database.

I want them to be representated as dd-MM-yyyy. Let's say I want to display 01-06-2016 into my database. When doing this with the code I gives me 0006-12-07. Strangely..when I change my pattern into does give me exactly what the pattern says: 2016-06-01. But it doesn't work the other way round.

String parameter = request.getParameter("instroomdatum");
SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy");
try {
Date parsed = sdf.parse(parameter);
java.sql.Date sql = new java.sql.Date(parsed.getTime());
} catch (ParseException ex) {
Logger.getLogger(StudentController.class.getName()).log(Level.SEVERE, null, ex);

Can somebody please explain me what's going on and how to fix this problem? It's really annoying.

EDIT: I tried printing the value of parameter with a simple PrintWriter-object for the specific date 01-06-2016. It shows me 2016-06-01, even though my pattern in the code above is set to dd-MM-yyyy.

Answer Source

You are confusing the display format with the internal representation.

Dates in a database are not represented in any specific display format, such as YYYY-MM-DD. Database dates are normally stored in a numeric form that represents a certain number of seconds and milliseconds (or nanoseconds) from some fixed starting point.

The display format is applied dynamically when you query the database and ask for the date/time as a string, but if you ask for it as a Date object, you get the internal representation, encapsulated in a java.sql.Date.

It is up to your Java code to format the date as you need it.

In your particular example (according to your comment), the string returned by your input method is 2016-06-01, so you need to parse it with the pattern yyyy-MM-dd. This will correctly convert the external representation to a valid Date object.

But how should i specifically change this representation to dd-MM-yyyy

Once you have it as Date, you can immediately turn around and convert the Date back into a String with a different SimpleDateFormat specification.

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