Ytukyg

Here is an example:

public MyDate() throws ParseException {

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");

    sdf.setLenient(false);

    String t1 = "2011/12/12aaa";

    System.out.println(sdf.parse(t1));

}

2011/12/12aaa is not a valid date string. However the function prints "Mon Dec 12 00:00:00 PST 2011" and ParseException isn't thrown.

Can anyone tell me how to let SimpleDateFormat treat "2011/12/12aaa" as an invalid date string and throw an exception?

The JavaDoc on parse(...) states the following:

parsing does not necessarily use all characters up to the end of the string

It seems like you can't make SimpleDateFormat throw an exception, but you can do the following:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");

sdf.setLenient(false);

ParsePosition p = new ParsePosition( 0 );

String t1 = "2011/12/12aaa";    

System.out.println(sdf.parse(t1,p));



if(p.getIndex() < t1.length()) {

  throw new ParseException( t1, p.getIndex() );

}

Basically, you check whether the parse consumed the entire string and if not you have invalid input.

To chack whether a date is valid
The following method returns if the date is in valid otherwise it will return false.

public boolean isValidDate(String date) {



        SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");

        Date testDate = null;

        try {

            testDate = sdf.parse(date);

        }

        catch (ParseException e) {

            return false;

        }

        if (!sdf.format(testDate).equals(date)) {

            return false;

        }

        return true;



    }

Have a look on the following class which can check whether the date is valid or not

** Sample Example**

import java.text.ParseException;

import java.text.SimpleDateFormat;

import java.util.Date;



public class DateValidCheck {





    public static void main(String args) {



        if(new DateValidCheck().isValidDate("2011/12/12aaa")){

            System.out.println("...date is valid");

        }else{

            System.out.println("...date is invalid...");

        }



    }





    public boolean isValidDate(String date) {



        SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");

        Date testDate = null;

        try {

            testDate = sdf.parse(date);

        }

        catch (ParseException e) {

            return false;

        }

        if (!sdf.format(testDate).equals(date)) {

            return false;

        }

        return true;



    }



}

After it successfully parsed the entire pattern string SimpleDateFormat stops evaluating the data it was given to parse.

Java 8 LocalDate may be used:

public static boolean isDate(String date) {

try {

        LocalDate.parse(date, DateTimeFormatter.ofPattern("yyyy/MM/dd"));

        return true;

    } catch (DateTimeParseException e) {

        return false;

    }

}

If input argument is "2011/12/12aaaaaaaaa", output is false;

If input argument is "2011/12/12", output is true

Take a look on the method documentation which says: ParseException if the beginning of the specified string cannot be parsed.

Method source code with javadoc:

/**

 * Parses text from the beginning of the given string to produce a date.

 * The method may not use the entire text of the given string.

 * <p>

 * See the {@link #parse(String, ParsePosition)} method for more information

 * on date parsing.

 *

 * @param source A <code>String</code> whose beginning should be parsed.

 * @return A <code>Date</code> parsed from the string.

 * @exception ParseException if the beginning of the specified string

 *            cannot be parsed.

 */

public Date parse(String source) throws ParseException

{

    ParsePosition pos = new ParsePosition(0);

    Date result = parse(source, pos);

    if (pos.index == 0)

        throw new ParseException("Unparseable date: "" + source + """ ,

            pos.errorIndex);

    return result;

}

You can use the ParsePosition class or the sdf.setLenient(false) function

Docs:
http://docs.oracle.com/javase/7/docs/api/java/text/ParsePosition.html
http://docs.oracle.com/javase/7/docs/api/java/text/DateFormat.html#setLenient(boolean)