Im trying to check the format of the Date.

Implementation: Get Date format yyyy-MM-dd then if i input beyond month 12 and day 30 or 31 depend on the month it must show error.

The pattern will work if I manually setup a date in String, but the date must come from Date to String but the Date will auto adjust.

Try the code here: https://www.programiz.com/java-programming/online-compiler/

    import java.text.DateFormat;
    import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.time.LocalDate;
    import java.time.ZoneId;
    import java.time.format.DateTimeFormatter;
    import java.time.format.DateTimeParseException;
    import java.time.temporal.TemporalAccessor;
    import java.util.Calendar;
    import java.util.Date;
    import java.time.Instant;
    import java.util.GregorianCalendar;
    import java.time.LocalDateTime;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    
    
    class HelloWorld {
        public static void main(String[] args) {
    
            Date date = new GregorianCalendar(2015, 11, 33).getTime();  
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
        formatter.setLenient(false);
        String strDate = formatter.format(date); 
        
          
            
             Pattern dateFrmtPtrn =  Pattern.compile(
                        "((19|20)\\d\\d)"
                                  "-"
                          "(0?[1-9]|1[012])"
                          "-"
                        
                         "(0?[1-9]|[12][0-9]|3[01])"
                        );
    Matcher mtch = dateFrmtPtrn.matcher(strDate);
            
            if(mtch.matches(
            )){
                
                System.out.println(strDate);
            }else{
                System.out.println("Error");
            }
          
        }
    }
    //Must Error
    //Output: 2016-01-02

The manual with String only. This will work.

    import java.text.DateFormat;
    import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.time.LocalDate;
    import java.time.ZoneId;
    import java.time.format.DateTimeFormatter;
    import java.time.format.DateTimeParseException;
    import java.time.temporal.TemporalAccessor;
    import java.util.Calendar;
    import java.util.Date;
    import java.time.Instant;
    import java.util.GregorianCalendar;
    import java.time.LocalDateTime;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    
    
    class HelloWorld {
        public static void main(String[] args) {
    
        
        //  String datey = "2023-12-32";
          String datey = "2023-13-32";
            
             Pattern dateFrmtPtrn =  Pattern.compile(
                        "((19|20)\\d\\d)"
                                  "-"
                          "(0?[1-9]|1[012])"
                          "-"
                        
                         "(0?[1-9]|[12][0-9]|3[01])"
                        );
    Matcher mtch = dateFrmtPtrn.matcher(datey);
            
            if(mtch.matches(
            )){
                
                System.out.println(datey);
            }else{
                System.out.println("Error");
            }
          
        }
    }
    
    //working
    //Output: Error

CodePudding user response：

If you switched to a java.time.LocalDate, you could use the Exceptions that get thrown when you try to initialize a LocalDate with invalid values:

Let's say you just want to create a LocalDate with given int values for year, month of year and day of month. You could try to initialize one and print the error message of the DateTimeException thrown.

e.g. the following code will print an error:

try {
    // try to create December 32. 2022
    LocalDate invLocDat = LocalDate.of(2022, 12, 32);
    System.out.println("Created LocalDate: "   invLocDat);
} catch (DateTimeException dte) {
    // print what the exception says
    System.err.println(dte.getMessage());
}

The message printed will be

Invalid value for DayOfMonth (valid values 1 - 28/31): 32

You could find out an invalid month of year, too, e.g. LocalDate.of(2022, 13, 31) would cause the above code to print

Invalid value for MonthOfYear (valid values 1 - 12): 13

And a valid input would simply print the toString() method of the successfully created LocalDate. Use a DateTimeFormatter if you want different output.

CodePudding user response：

Default behaviour of Calendar is to be lenient.

When you write Date date = new GregorianCalendar(2015, 11, 33).getTime(); you are getting the Date value of a lenient calendar, so the 33th day after the 1st of december.

In your code, you set the formatter to be lenient which is useless as the date you want to format is already adjusted.

To avoid that, create a calendar, set it non-lenient and then set the expected date. But note that in this case the formatter will not return any invalid date as the Date object will always be valid.