Convert String to Date From yyyy-mm-dd to dd-mm-yyyy format

Question

I made a Java endpoint that contains the date information. The date is received as string in the format 'yyyy-mm-dd'. I need to convert to Date dd-mm-yyyy format. I am using the following format which is in error. Could someone help me?

@RequestMapping(value="/get/{numeroNotaFiscal}/{cnpj}/{dataNotaFiscal}", method = RequestMethod.GET)
public @ResponseBody Boolean NotaFiscalDataCnpj(@PathVariable String numeroNotaFiscal, @PathVariable String cnpj, @PathVariable String dataNotaFiscal) {
    DB2DAOSo sofv = new DB2DAOSo();
    //Converte de String para Date
    DateFormat formatUS = new SimpleDateFormat("yyyy-mm-dd");
    Date date = formatUS.parse(dataNotaFiscal);

    DateFormat formatBR = new SimpleDateFormat("dd-mm-yyyy");
    String dataConvertida = formatBR.format(date);
    
    Boolean resposta = sofvdnrf.getNotaFiscalDataCnpj(numeroNotaFiscal, cnpj, dataConvertida);
    return resposta;
}

Answer 1

According to the documentation, for the month you should use the uppercase "M". The lowercase "m" is minutes.

Then I would be:

DateFormat formatUS = new SimpleDateFormat("yyyy-MM-dd");
Date date = formatUS.parse(dataNotaFiscal);

DateFormat formatBR = new SimpleDateFormat("dd-MM-yyyy");
String dataConvertida = formatBR.format(date);

One detail is that SimpleDateFormat is very permissive and accepts invalid dates such as "2020-99-99" (and the results are quite "weird", read more here and here). To avoid these cases, you can set the lenient mode to false:

DateFormat formatUS = new SimpleDateFormat("yyyy-MM-dd");
formatUS.setLenient(false); // assim não aceita datas inválidas
Date date = formatUS.parse(dataNotaFiscal);
... etc

This way, invalid dates will make an exception.

---

If you are using Java >= 8, another option is to use the API java.time. For your case, which has only day, month and year, can be used a java.time.LocalDate, and to format, use a java.time.format.DateTimeFormatter:

LocalDate data = LocalDate.parse(dataNotaFiscal);
DateTimeFormatter fmt = DateTimeFormatter.ofPattern("dd-MM-uuuu");
String dataConvertida = fmt.format(data);

---

Detail that method parse by default already works with the format "year-month-day" (which is the format defined by ISO 8601 standard). But if the string was in another format, just create another DateTimeFormatter and pass it to the method parse. Ex:

// supondo que a string está em outro formato
DateTimeFormatter parser = DateTimeFormatter.ofPattern("dd/MM/uuuu")
    .withResolverStyle(ResolverStyle.STRICT); // para não aceitar datas inválidas
LocalDate data = LocalDate.parse("20/01/2020", parser);
etc..

Also note the use of "u" instead of "y" for the year. For more details, see here.

As to the use of ResolverStyle, it is because of default the parser accepts some invalid dates, such as 31/04/2020 (as April only has 30 days). See more details in replies of this question.