Java: Check the date format of current string is according to required format or not [duplicate]

Question

I wanted to know that is there any method available in Java that can do this.Otherwise I may go for Regex solution.

I have input string from user that can be any characters. And I want to check that the input string is according to my required date format or not.

As I have input 20130925 and my required format is dd/MM/yyyy so, for this case I should get false.

I don't want to convert this date I just want to check whether input string is according to required date format or not.

I have tried following

Date date = null; try { date = new SimpleDateFormat("dd/MM/yyyy").parse("20130925"); } catch (Exception ex) { // do something for invalid dateformat } 

but my catch (Exception ex) block is unable to catch any exceptions generated by SimpleDateFormat.Parse();

Answer 1

Disclaimer

Parsing a string back to date/time value in an unknown format is inherently impossible (let's face it, what does 3/3/3 actually mean?!), all we can do is "best effort"

Important

This solution doesn't throw an Exception, it returns a boolean, this is by design. Any Exceptions are used purely as a guard mechanism.

2018

Since it's now 2018 and Java 8+ has the date/time API (and the rest have the ThreeTen backport). The solution remains basically the same, but becomes slightly more complicated, as we need to perform checks for:

• date and time
• date only
• time only

This makes it look something like...

public static boolean isValidFormat(String format, String value, Locale locale) {     LocalDateTime ldt = null;     DateTimeFormatter fomatter = DateTimeFormatter.ofPattern(format, locale);      try {         ldt = LocalDateTime.parse(value, fomatter);         String result = ldt.format(fomatter);         return result.equals(value);     } catch (DateTimeParseException e) {         try {             LocalDate ld = LocalDate.parse(value, fomatter);             String result = ld.format(fomatter);             return result.equals(value);         } catch (DateTimeParseException exp) {             try {                 LocalTime lt = LocalTime.parse(value, fomatter);                 String result = lt.format(fomatter);                 return result.equals(value);             } catch (DateTimeParseException e2) {                 // Debugging purposes                 //e2.printStackTrace();             }         }     }      return false; } 

This makes the following...

System.out.println("isValid - dd/MM/yyyy with 20130925 = " + isValidFormat("dd/MM/yyyy", "20130925", Locale.ENGLISH)); System.out.println("isValid - dd/MM/yyyy with 25/09/2013 = " + isValidFormat("dd/MM/yyyy", "25/09/2013", Locale.ENGLISH)); System.out.println("isValid - dd/MM/yyyy with 25/09/2013 12:13:50 = " + isValidFormat("dd/MM/yyyy", "25/09/2013  12:13:50", Locale.ENGLISH)); System.out.println("isValid - yyyy-MM-dd with 2017-18--15 = " + isValidFormat("yyyy-MM-dd", "2017-18--15", Locale.ENGLISH)); 

output...

isValid - dd/MM/yyyy with 20130925 = false isValid - dd/MM/yyyy with 25/09/2013 = true isValid - dd/MM/yyyy with 25/09/2013 12:13:50 = false isValid - yyyy-MM-dd with 2017-18--15 = false 

Original Answer

Simple try and parse the String to the required Date using something like SimpleDateFormat

Date date = null; try {     SimpleDateFormat sdf = new SimpleDateFormat(format);     date = sdf.parse(value);     if (!value.equals(sdf.format(date))) {         date = null;     } } catch (ParseException ex) {     ex.printStackTrace(); } if (date == null) {     // Invalid date format } else {     // Valid date format } 

You could then simply write a simple method that performed this action and returned true when ever Date was not null...

As a suggestion...

Updated with running example

I'm not sure what you are doing, but, the following example...

import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date;  public class TestDateParser {      public static void main(String[] args) {         System.out.println("isValid - dd/MM/yyyy with 20130925 = " + isValidFormat("dd/MM/yyyy", "20130925"));         System.out.println("isValid - dd/MM/yyyy with 25/09/2013 = " + isValidFormat("dd/MM/yyyy", "25/09/2013"));         System.out.println("isValid - dd/MM/yyyy with 25/09/2013 12:13:50 = " + isValidFormat("dd/MM/yyyy", "25/09/2013  12:13:50"));     }      public static boolean isValidFormat(String format, String value) {         Date date = null;         try {             SimpleDateFormat sdf = new SimpleDateFormat(format);             date = sdf.parse(value);             if (!value.equals(sdf.format(date))) {                 date = null;             }         } catch (ParseException ex) {             ex.printStackTrace();         }         return date != null;     }  } 

Outputs (something like)...

java.text.ParseException: Unparseable date: "20130925" isValid - dd/MM/yyyy with 20130925 = false isValid - dd/MM/yyyy with 25/09/2013 = true isValid - dd/MM/yyyy with 25/09/2013 12:13:50 = false     at java.text.DateFormat.parse(DateFormat.java:366)     at javaapplication373.JavaApplication373.isValidFormat(JavaApplication373.java:28)     at javaapplication373.JavaApplication373.main(JavaApplication373.java:19) 

Not correct. For isValidFormat("yyyy-MM-dd", "2017-18--15"); not throw any Exception.

isValid - yyyy-MM-dd", "2017-18--15 = false 

Seems to work as expected for me - the method doesn't rely on (nor does it throw) the exception alone to perform it's operation