Java - How to check if a value is of type Date

Question

I have a project requirement. There are values in a .txt as -

 02/01/2017 00:00:00

Now I need to have some rules to check if this value in the data file is of type Date. How can I do that? Thanks. I am new to Java so any help much appreciated. Thanks

Answer 1

Try to parse it to date. If it throws ParseException then it is not a date.

String dateString = "02/01/2017 00:00:00";
DateFormat df = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss"); 
Date date;
try {
    date = df.parse(dateString);
} catch (ParseException e) {
    e.printStackTrace();
}

Answer 2

If you just want valid days, use non-lenient parsing:

String dateString = "02/28/2017 00:00:00";

DateFormat df = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
df.setLenient(false);
Date date;
try {
    date = df.parse(dateString);
    System.out.println(date);
} catch (ParseException e) {
    e.printStackTrace();
}

This will throw an exception for non-existing days like the 31st of February

Answer 3

1. Methord 1

   Date dt = new Date(); //this should your Dynamic object
   
   if (dt.getClass().equals(new Date().getClass())) 
   {
     //if its date object
   }
   

2. Methord 2

    if(dt instanceof  Date){
      //if its date object
    }
   

Answer 4

Use this to check date

String sDate1="31/12/1998 00:00:00";  
try{
  Date date1=new SimpleDateFormat("dd/MM/yyyy hh:mm:ss").parse(sDate1);  `
} 
catch(Exception e)
{
  //Not a date..
} 

Answer 5

You can use regular expressions to check the format

public boolean isDate(String s){
String pattern= "([0-9]{2})/([0-9]{2})/([0-9]{4}) ([0-9]{2}):([0-9]{2}):([0-9]{2})";
return s.matches(pattern);}

Answer 6

Here’s the Java 8 solution (it can be made to work in Java 6 and 7 too when you use the ThreeTen Backport).

private static final DateTimeFormatter DATE_TIME_FORMAT 
        = DateTimeFormatter.ofPattern("MM/dd/uuuu HH:mm:ss")
                .withResolverStyle(ResolverStyle.STRICT);

public static boolean hasTypeDate(String stringFromTxt) {
    try {
        DATE_TIME_FORMAT.parse(stringFromTxt);
        return true;
    } catch (DateTimeParseException dtpe) {
        return false;
    }
}

Stay away from SimpleDateFormat for new code. It has had its time, it’s been outdated for a while now.

If you intended the day of month first (if 02/01/2017 means January 2nd), you need the format pattern dd/MM/uuuu HH:mm:ss instead.

If you need to know which date and time was in the .txt, use:

        LocalDateTime dateTime = LocalDateTime.parse(stringFromTxt, DATE_TIME_FORMAT);

Link: ThreeTen Backport: java.time classes for Java 6 and 7.

Answer 7

public static boolean isValidDate(String inDate) {
    SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
    dateFormat.setLenient(false);
    try {
      dateFormat.parse(inDate.trim());
    } catch (ParseException pe) {
      return false;
    }
    return true;
  }

public static void main(String[] args) {
 String file = "/path/to/your/file.txt";

try {

    BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
    String line;
    while ((line = br.readLine()) != null) {
        // do something with line
    }
    br.close();
   isValidDate(line));
   //do what you want :)
  }