Formatting dates for display and storage

With the help of colleagues and some modifications to the code, I got the desired effect.

This method returns a string formatted as a system date, from a string in the format yyyy-MM-dd. Enter 2017-01-26, exit 26-1-17 or 1-26-17, according to device settings.

public String convertDateToShow(String strDate){
    // formato de entrada deve ser 2017-01-17
    SimpleDateFormat dateFormatIn = new SimpleDateFormat("yyyy-MM-dd", Locale.US);
    // sem argumentos, pega o formato do sistema para exibir a data
    SimpleDateFormat dateFormatOut = new SimpleDateFormat();
    // com argumentos formato e locale a saida e sempre a mesma
    //  SimpleDateFormat dateFormatOut = new SimpleDateFormat("dd-MM-yy", Locale.US);
    Date convertedDate = new Date();
    try {
        convertedDate = dateFormatIn.parse(strDate);
    } catch (ParseException e) {
            e.printStackTrace();
    }


    return stringToSpace(String.valueOf(dateFormatOut.format(convertedDate)));
}

// stringToSpace() retorna a string a esquerda do primeiro espaço da string passada.
// necessario porque a conversao retorna dd/MM/yy 12:00 hs
private String stringToSpace(String string){

    int spaceIndex = string.indexOf(" ");
    if(spaceIndex > 0) {
        string = string.substring(0, spaceIndex);
    }
    return string;
}

Returns a string formatted as a date in the format yyyy-MM-dd, from a string formatted as a system date. Enter 26-1-17 or 1-26-17 and exit 2017-26-01.

public String convertDateToStore(String strDate){
    // formato de entrada do sistema (dd-MM-yy ou MM-dd-yy ou...)
    // sem argumentos, pega o formato do sistema para exibir a data
    SimpleDateFormat dateFormatIn = new SimpleDateFormat();
    // com argumentos formato e locale a saida e sempre a mesma
    // SimpleDateFormat dateFormatIn = new SimpleDateFormat("dd-MM-yy", Locale.US);
    SimpleDateFormat dateFormatOut = new SimpleDateFormat("yyyy-MM-dd", Locale.US);

    Date convertedDate = new Date();
    try {
        convertedDate = dateFormatIn.parse(strDate);
    } catch (ParseException e) {
            e.printStackTrace();
    }
    return String.valueOf(dateFormatOut.format(convertedDate));
}

E zefini.

This error happens because you do not put the input format in SimpleDateFormat, try changing the line below

From:

formatFrom = new SimpleDateFormat();

To:

formatFrom = new SimpleDateFormat("dd/MM/yy");

You can also use a single method to reuse the code, instead of using two methods that are practically the same:

private String strToDate(String dateToFormat, String formatIn, String formatOut){
    // format date
    SimpleDateFormat formatFrom, formatTo;
    formatFrom = new SimpleDateFormat(formatIn);
    formatTo = new SimpleDateFormat(formatOut);
    if(dateToFormat != null) {
        try {
            Date mDate = formatFrom.parse(dateToFormat); // <-- aqui ocorre a exceção.
            dateToFormat = formatTo.format(mDate);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    if(dateToFormat == null){
        dateToFormat = formatTo.format(new Date());
    }
    return stringToSpace(dateToFormat);
}

And call the same method but with different parameters.

For reading:

String dataLeitura = strToDate(data, "yyyy-MM-dd", "dd/MM/yy");

And for writing:

String dataEscrita = strToDate(data, "dd/MM/yy", "yyyy-MM-dd");

What you have to note is that you are entering a format different from what you are using in SimpleDateFormat() . Basically you have to use two formats, one input and one output. For input in this case would be 26/01/17 and output 2017-01-26 , then the parameter of method SimplesDateFormat() respectively would be dd-MM-yy input and yyyy-MM-dd output. See the method below how the problem can be solved:

public String convertStringInDate(String str){
    // formato de entrada deve ser 26/01/17 
    SimpleDateFormat dateFormatIn = new SimpleDateFormat("dd-MM-yy", Locale.US);
    SimpleDateFormat dateFormatInOut = new SimpleDateFormat("yyyy-MM-dd", Locale.US);

    Date convertedDate = new Date();
    try {
        convertedDate = dateFormatIn.parse(str);
    } catch (ParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return String.valueOf(dateFormatInOut.format(convertedDate));
}

For more details, see in the documentation (en) .

EDIT

In order to set the locale to SimpleDateFormat , although sometimes set to getDefault() , care must be taken because it may not be appropriate for all use cases, especially output read devices. See a note in the documentation :

  

The default location is not appropriate for   device. The best option is usually Locale.US - this location   is guaranteed to be available on all devices, and is   frequently used.

See more details here. .