2楼-- · 2019-01-03 15:55

java.time

The proper (and easy) way to do date/time validation using Java 8+ is to use the java.time.format.DateTimeFormatter class. Using a regex for validation isn't really ideal for dates. For the example case in this question:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");

try {
    LocalDate date = formatter.parse(text, LocalDate::from);
} catch (DateTimeParseException e) {
    // Thrown if text could not be parsed in the specified format
}

This code will parse the text, validate that it is a valid date, and also return the date as a LocalDate object. Note that the DateTimeFormatter class has a number of static predefined date formats matching ISO standards if your use case matches any of them.

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ら.Afraid

3楼-- · 2019-01-03 15:56

Use the following regular expression:

^\d{4}-\d{2}-\d{2}$

as in

if (str.matches("\\d{4}-\\d{2}-\\d{2}")) {
    ...
}

With the matches method, the anchors ^ and $ (beginning and end of string, respectively) are present implicitly.

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乱世女痞

4楼-- · 2019-01-03 15:56

I would go with a simple regex which will check that days doesn't have more than 31 days and months no more than 12. Something like:

(0?[1-9]|[12][0-9]|3[01])-(0?[1-9]|1[012])-((18|19|20|21)\\d\\d)

This is the format "dd-MM-yyyy". You can tweak it to your needs (for example take off the ? to make the leading 0 required - now its optional), and then use a custom logic to cut down to the specific rules like leap years February number of days case, and other months number of days cases. See the DateChecker code below.

I am choosing this approach since I tested that this is the best one when performance is taken into account. I checked this (1st) approach versus 2nd approach of validating a date against a regex that takes care of the other use cases, and 3rd approach of using the same simple regex above in combination with SimpleDateFormat.parse(date).
The 1st approach was 4 times faster than the 2nd approach, and 8 times faster than the 3rd approach. See the self contained date checker and performance tester main class at the bottom. One thing that I left unchecked is the joda time approach(s). (The more efficient date/time library).

Date checker code:

class DateChecker {

    private Matcher matcher;
    private Pattern pattern;

    public DateChecker(String regex) {
        pattern = Pattern.compile(regex);
    }

    /**
     * Checks if the date format is a valid.
     * Uses the regex pattern to match the date first. 
     * Than additionally checks are performed on the boundaries of the days taken the month into account (leap years are covered).
     * 
     * @param date the date that needs to be checked.
     * @return if the date is of an valid format or not.
     */
    public boolean check(final String date) {
        matcher = pattern.matcher(date);
        if (matcher.matches()) {
            matcher.reset();
            if (matcher.find()) {
                int day = Integer.parseInt(matcher.group(1));
                int month = Integer.parseInt(matcher.group(2));
                int year = Integer.parseInt(matcher.group(3));

                switch (month) {
                case 1:
                case 3:
                case 5:
                case 7:
                case 8:
                case 10:
                case 12: return day < 32;
                case 4:
                case 6:
                case 9:
                case 11: return day < 31;
                case 2: 
                    int modulo100 = year % 100;
                    //http://science.howstuffworks.com/science-vs-myth/everyday-myths/question50.htm
                    if ((modulo100 == 0 && year % 400 == 0) || (modulo100 != 0 && year % LEAP_STEP == 0)) {
                        //its a leap year
                        return day < 30;
                    } else {
                        return day < 29;
                    }
                default:
                    break;
                }
            }
        }
        return false;
    }

    public String getRegex() {
        return pattern.pattern();
    }
}

Date checking/testing and performance testing:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Tester {

    private static final String[] validDateStrings = new String[]{
        "1-1-2000", //leading 0s for day and month optional
        "01-1-2000", //leading 0 for month only optional
        "1-01-2000", //leading 0 for day only optional
        "01-01-1800", //first accepted date
        "31-12-2199", //last accepted date
        "31-01-2000", //January has 31 days
        "31-03-2000", //March has 31 days
        "31-05-2000", //May has 31 days
        "31-07-2000", //July has 31 days
        "31-08-2000", //August has 31 days
        "31-10-2000", //October has 31 days
        "31-12-2000", //December has 31 days
        "30-04-2000", //April has 30 days
        "30-06-2000", //June has 30 days
        "30-09-2000", //September has 30 days
        "30-11-2000", //November has 30 days
    };
    private static final String[] invalidDateStrings = new String[]{
        "00-01-2000", //there is no 0-th day
        "01-00-2000", //there is no 0-th month
        "31-12-1799", //out of lower boundary date
        "01-01-2200", //out of high boundary date
        "32-01-2000", //January doesn't have 32 days
        "32-03-2000", //March doesn't have 32 days
        "32-05-2000", //May doesn't have 32 days
        "32-07-2000", //July doesn't have 32 days
        "32-08-2000", //August doesn't have 32 days
        "32-10-2000", //October doesn't have 32 days
        "32-12-2000", //December doesn't have 32 days
        "31-04-2000", //April doesn't have 31 days
        "31-06-2000", //June doesn't have 31 days
        "31-09-2000", //September doesn't have 31 days
        "31-11-2000", //November doesn't have 31 days
        "001-02-2000", //SimpleDateFormat valid date (day with leading 0s) even with lenient set to false
        "1-0002-2000", //SimpleDateFormat valid date (month with leading 0s) even with lenient set to false
        "01-02-0003", //SimpleDateFormat valid date (year with leading 0s) even with lenient set to false
        "01.01-2000", //. invalid separator between day and month
        "01-01.2000", //. invalid separator between month and year
        "01/01-2000", /// invalid separator between day and month
        "01-01/2000", /// invalid separator between month and year
        "01_01-2000", //_ invalid separator between day and month
        "01-01_2000", //_ invalid separator between month and year
        "01-01-2000-12345", //only whole string should be matched
        "01-13-2000", //month bigger than 13
    };

    /**
     * These constants will be used to generate the valid and invalid boundary dates for the leap years. (For no leap year, Feb. 28 valid and Feb. 29 invalid; for a leap year Feb. 29 valid and Feb. 30 invalid)   
     */
    private static final int LEAP_STEP = 4;
    private static final int YEAR_START = 1800;
    private static final int YEAR_END = 2199;

    /**
     * This date regex will find matches for valid dates between 1800 and 2199 in the format of "dd-MM-yyyy".
     * The leading 0 is optional.
     */
    private static final String DATE_REGEX = "((0?[1-9]|[12][0-9]|3[01])-(0?[13578]|1[02])-(18|19|20|21)[0-9]{2})|((0?[1-9]|[12][0-9]|30)-(0?[469]|11)-(18|19|20|21)[0-9]{2})|((0?[1-9]|1[0-9]|2[0-8])-(0?2)-(18|19|20|21)[0-9]{2})|(29-(0?2)-(((18|19|20|21)(04|08|[2468][048]|[13579][26]))|2000))";

    /**
     * This date regex is similar to the first one, but with the difference of matching only the whole string. So "01-01-2000-12345" won't pass with a match.
     * Keep in mind that String.matches tries to match only the whole string.
     */
    private static final String DATE_REGEX_ONLY_WHOLE_STRING = "^" + DATE_REGEX + "$";

    /**
     * The simple regex (without checking for 31 day months and leap years):
     */
    private static final String DATE_REGEX_SIMPLE = "(0?[1-9]|[12][0-9]|3[01])-(0?[1-9]|1[012])-((18|19|20|21)\\d\\d)";

    /**
     * This date regex is similar to the first one, but with the difference of matching only the whole string. So "01-01-2000-12345" won't pass with a match.
     */
    private static final String DATE_REGEX_SIMPLE_ONLY_WHOLE_STRING = "^" + DATE_REGEX_SIMPLE + "$";

    private static final SimpleDateFormat SDF = new SimpleDateFormat("dd-MM-yyyy");
    static {
        SDF.setLenient(false);
    }

    private static final DateChecker dateValidatorSimple = new DateChecker(DATE_REGEX_SIMPLE);
    private static final DateChecker dateValidatorSimpleOnlyWholeString = new DateChecker(DATE_REGEX_SIMPLE_ONLY_WHOLE_STRING);

    /**
     * @param args
     */
    public static void main(String[] args) {
        DateTimeStatistics dateTimeStatistics = new DateTimeStatistics();
        boolean shouldMatch = true;
        for (int i = 0; i < validDateStrings.length; i++) {
            String validDate = validDateStrings[i];
            matchAssertAndPopulateTimes(
                    dateTimeStatistics,
                    shouldMatch, validDate);
        }

        shouldMatch = false;
        for (int i = 0; i < invalidDateStrings.length; i++) {
            String invalidDate = invalidDateStrings[i];

            matchAssertAndPopulateTimes(dateTimeStatistics,
                    shouldMatch, invalidDate);
        }

        for (int year = YEAR_START; year < (YEAR_END + 1); year++) {
            FebruaryBoundaryDates februaryBoundaryDates = createValidAndInvalidFebruaryBoundaryDateStringsFromYear(year);
            shouldMatch = true;
            matchAssertAndPopulateTimes(dateTimeStatistics,
                    shouldMatch, februaryBoundaryDates.getValidFebruaryBoundaryDateString());
            shouldMatch = false;
            matchAssertAndPopulateTimes(dateTimeStatistics,
                    shouldMatch, februaryBoundaryDates.getInvalidFebruaryBoundaryDateString());
        }

        dateTimeStatistics.calculateAvarageTimesAndPrint();
    }

    private static void matchAssertAndPopulateTimes(
            DateTimeStatistics dateTimeStatistics,
            boolean shouldMatch, String date) {
        dateTimeStatistics.addDate(date);
        matchAndPopulateTimeToMatch(date, DATE_REGEX, shouldMatch, dateTimeStatistics.getTimesTakenWithDateRegex());
        matchAndPopulateTimeToMatch(date, DATE_REGEX_ONLY_WHOLE_STRING, shouldMatch, dateTimeStatistics.getTimesTakenWithDateRegexOnlyWholeString());
        boolean matchesSimpleDateFormat = matchWithSimpleDateFormatAndPopulateTimeToMatchAndReturnMatches(date, dateTimeStatistics.getTimesTakenWithSimpleDateFormatParse());
        matchAndPopulateTimeToMatchAndReturnMatchesAndCheck(
                dateTimeStatistics.getTimesTakenWithDateRegexSimple(), shouldMatch,
                date, matchesSimpleDateFormat, DATE_REGEX_SIMPLE);
        matchAndPopulateTimeToMatchAndReturnMatchesAndCheck(
                dateTimeStatistics.getTimesTakenWithDateRegexSimpleOnlyWholeString(), shouldMatch,
                date, matchesSimpleDateFormat, DATE_REGEX_SIMPLE_ONLY_WHOLE_STRING);

        matchAndPopulateTimeToMatch(date, dateValidatorSimple, shouldMatch, dateTimeStatistics.getTimesTakenWithdateValidatorSimple());
        matchAndPopulateTimeToMatch(date, dateValidatorSimpleOnlyWholeString, shouldMatch, dateTimeStatistics.getTimesTakenWithdateValidatorSimpleOnlyWholeString());
    }

    private static void matchAndPopulateTimeToMatchAndReturnMatchesAndCheck(
            List<Long> times,
            boolean shouldMatch, String date, boolean matchesSimpleDateFormat, String regex) {
        boolean matchesFromRegex = matchAndPopulateTimeToMatchAndReturnMatches(date, regex, times);
        assert !((matchesSimpleDateFormat && matchesFromRegex) ^ shouldMatch) : "Parsing with SimpleDateFormat and date:" + date + "\nregex:" + regex + "\nshouldMatch:" + shouldMatch;
    }

    private static void matchAndPopulateTimeToMatch(String date, String regex, boolean shouldMatch, List<Long> times) {
        boolean matches = matchAndPopulateTimeToMatchAndReturnMatches(date, regex, times);
        assert !(matches ^ shouldMatch) : "date:" + date + "\nregex:" + regex + "\nshouldMatch:" + shouldMatch;
    }

    private static void matchAndPopulateTimeToMatch(String date, DateChecker dateValidator, boolean shouldMatch, List<Long> times) {
        long timestampStart;
        long timestampEnd;
        boolean matches;
        timestampStart = System.nanoTime();
        matches = dateValidator.check(date);
        timestampEnd = System.nanoTime();
        times.add(timestampEnd - timestampStart);
        assert !(matches ^ shouldMatch) : "date:" + date + "\ndateValidator with regex:" + dateValidator.getRegex() + "\nshouldMatch:" + shouldMatch;
    }

    private static boolean matchAndPopulateTimeToMatchAndReturnMatches(String date, String regex, List<Long> times) {
        long timestampStart;
        long timestampEnd;
        boolean matches;
        timestampStart = System.nanoTime();
        matches = date.matches(regex);
        timestampEnd = System.nanoTime();
        times.add(timestampEnd - timestampStart);
        return matches;
    }

    private static boolean matchWithSimpleDateFormatAndPopulateTimeToMatchAndReturnMatches(String date, List<Long> times) {
        long timestampStart;
        long timestampEnd;
        boolean matches = true;
        timestampStart = System.nanoTime();
        try {
            SDF.parse(date);
        } catch (ParseException e) {
            matches = false;
        } finally {
            timestampEnd = System.nanoTime();
            times.add(timestampEnd - timestampStart);
        }
        return matches;
    }

    private static FebruaryBoundaryDates createValidAndInvalidFebruaryBoundaryDateStringsFromYear(int year) {
        FebruaryBoundaryDates februaryBoundaryDates;
        int modulo100 = year % 100;
        //http://science.howstuffworks.com/science-vs-myth/everyday-myths/question50.htm
        if ((modulo100 == 0 && year % 400 == 0) || (modulo100 != 0 && year % LEAP_STEP == 0)) {
            februaryBoundaryDates = new FebruaryBoundaryDates(
                    createFebruaryDateFromDayAndYear(29, year), 
                    createFebruaryDateFromDayAndYear(30, year)
                    );
        } else {
            februaryBoundaryDates = new FebruaryBoundaryDates(
                    createFebruaryDateFromDayAndYear(28, year), 
                    createFebruaryDateFromDayAndYear(29, year)
                    );
        }
        return februaryBoundaryDates;
    }

    private static String createFebruaryDateFromDayAndYear(int day, int year) {
        return String.format("%d-02-%d", day, year);
    }

    static class FebruaryBoundaryDates {
        private String validFebruaryBoundaryDateString;
        String invalidFebruaryBoundaryDateString;
        public FebruaryBoundaryDates(String validFebruaryBoundaryDateString,
                String invalidFebruaryBoundaryDateString) {
            super();
            this.validFebruaryBoundaryDateString = validFebruaryBoundaryDateString;
            this.invalidFebruaryBoundaryDateString = invalidFebruaryBoundaryDateString;
        }
        public String getValidFebruaryBoundaryDateString() {
            return validFebruaryBoundaryDateString;
        }
        public void setValidFebruaryBoundaryDateString(
                String validFebruaryBoundaryDateString) {
            this.validFebruaryBoundaryDateString = validFebruaryBoundaryDateString;
        }
        public String getInvalidFebruaryBoundaryDateString() {
            return invalidFebruaryBoundaryDateString;
        }
        public void setInvalidFebruaryBoundaryDateString(
                String invalidFebruaryBoundaryDateString) {
            this.invalidFebruaryBoundaryDateString = invalidFebruaryBoundaryDateString;
        }
    }

    static class DateTimeStatistics {
        private List<String> dates = new ArrayList<String>();
        private List<Long> timesTakenWithDateRegex = new ArrayList<Long>();
        private List<Long> timesTakenWithDateRegexOnlyWholeString = new ArrayList<Long>();
        private List<Long> timesTakenWithDateRegexSimple = new ArrayList<Long>();
        private List<Long> timesTakenWithDateRegexSimpleOnlyWholeString = new ArrayList<Long>();
        private List<Long> timesTakenWithSimpleDateFormatParse = new ArrayList<Long>();
        private List<Long> timesTakenWithdateValidatorSimple = new ArrayList<Long>();
        private List<Long> timesTakenWithdateValidatorSimpleOnlyWholeString = new ArrayList<Long>();
        public List<String> getDates() {
            return dates;
        }
        public List<Long> getTimesTakenWithDateRegex() {
            return timesTakenWithDateRegex;
        }
        public List<Long> getTimesTakenWithDateRegexOnlyWholeString() {
            return timesTakenWithDateRegexOnlyWholeString;
        }
        public List<Long> getTimesTakenWithDateRegexSimple() {
            return timesTakenWithDateRegexSimple;
        }
        public List<Long> getTimesTakenWithDateRegexSimpleOnlyWholeString() {
            return timesTakenWithDateRegexSimpleOnlyWholeString;
        }
        public List<Long> getTimesTakenWithSimpleDateFormatParse() {
            return timesTakenWithSimpleDateFormatParse;
        }
        public List<Long> getTimesTakenWithdateValidatorSimple() {
            return timesTakenWithdateValidatorSimple;
        }
        public List<Long> getTimesTakenWithdateValidatorSimpleOnlyWholeString() {
            return timesTakenWithdateValidatorSimpleOnlyWholeString;
        }
        public void addDate(String date) {
            dates.add(date);
        }
        public void addTimesTakenWithDateRegex(long time) {
            timesTakenWithDateRegex.add(time);
        }
        public void addTimesTakenWithDateRegexOnlyWholeString(long time) {
            timesTakenWithDateRegexOnlyWholeString.add(time);
        }
        public void addTimesTakenWithDateRegexSimple(long time) {
            timesTakenWithDateRegexSimple.add(time);
        }
        public void addTimesTakenWithDateRegexSimpleOnlyWholeString(long time) {
            timesTakenWithDateRegexSimpleOnlyWholeString.add(time);
        }
        public void addTimesTakenWithSimpleDateFormatParse(long time) {
            timesTakenWithSimpleDateFormatParse.add(time);
        }
        public void addTimesTakenWithdateValidatorSimple(long time) {
            timesTakenWithdateValidatorSimple.add(time);
        }
        public void addTimesTakenWithdateValidatorSimpleOnlyWholeString(long time) {
            timesTakenWithdateValidatorSimpleOnlyWholeString.add(time);
        }

        private void calculateAvarageTimesAndPrint() {
            long[] sumOfTimes = new long[7];
            int timesSize = timesTakenWithDateRegex.size();
            for (int i = 0; i < timesSize; i++) {
                sumOfTimes[0] += timesTakenWithDateRegex.get(i);
                sumOfTimes[1] += timesTakenWithDateRegexOnlyWholeString.get(i);
                sumOfTimes[2] += timesTakenWithDateRegexSimple.get(i);
                sumOfTimes[3] += timesTakenWithDateRegexSimpleOnlyWholeString.get(i);
                sumOfTimes[4] += timesTakenWithSimpleDateFormatParse.get(i);
                sumOfTimes[5] += timesTakenWithdateValidatorSimple.get(i);
                sumOfTimes[6] += timesTakenWithdateValidatorSimpleOnlyWholeString.get(i);
            }
            System.out.println("AVG from timesTakenWithDateRegex (in nanoseconds):" + (double) sumOfTimes[0] / timesSize);
            System.out.println("AVG from timesTakenWithDateRegexOnlyWholeString (in nanoseconds):" + (double) sumOfTimes[1] / timesSize);
            System.out.println("AVG from timesTakenWithDateRegexSimple (in nanoseconds):" + (double) sumOfTimes[2] / timesSize);
            System.out.println("AVG from timesTakenWithDateRegexSimpleOnlyWholeString (in nanoseconds):" + (double) sumOfTimes[3] / timesSize);
            System.out.println("AVG from timesTakenWithSimpleDateFormatParse (in nanoseconds):" + (double) sumOfTimes[4] / timesSize);
            System.out.println("AVG from timesTakenWithDateRegexSimple + timesTakenWithSimpleDateFormatParse (in nanoseconds):" + (double) (sumOfTimes[2] + sumOfTimes[4]) / timesSize);
            System.out.println("AVG from timesTakenWithDateRegexSimpleOnlyWholeString + timesTakenWithSimpleDateFormatParse (in nanoseconds):" + (double) (sumOfTimes[3] + sumOfTimes[4]) / timesSize);
            System.out.println("AVG from timesTakenWithdateValidatorSimple (in nanoseconds):" + (double) sumOfTimes[5] / timesSize);
            System.out.println("AVG from timesTakenWithdateValidatorSimpleOnlyWholeString (in nanoseconds):" + (double) sumOfTimes[6] / timesSize);
        }
    }

    static class DateChecker {

        private Matcher matcher;
        private Pattern pattern;

        public DateChecker(String regex) {
            pattern = Pattern.compile(regex);
        }

        /**
         * Checks if the date format is a valid.
         * Uses the regex pattern to match the date first. 
         * Than additionally checks are performed on the boundaries of the days taken the month into account (leap years are covered).
         * 
         * @param date the date that needs to be checked.
         * @return if the date is of an valid format or not.
         */
        public boolean check(final String date) {
            matcher = pattern.matcher(date);
            if (matcher.matches()) {
                matcher.reset();
                if (matcher.find()) {
                    int day = Integer.parseInt(matcher.group(1));
                    int month = Integer.parseInt(matcher.group(2));
                    int year = Integer.parseInt(matcher.group(3));

                    switch (month) {
                    case 1:
                    case 3:
                    case 5:
                    case 7:
                    case 8:
                    case 10:
                    case 12: return day < 32;
                    case 4:
                    case 6:
                    case 9:
                    case 11: return day < 31;
                    case 2: 
                        int modulo100 = year % 100;
                        //http://science.howstuffworks.com/science-vs-myth/everyday-myths/question50.htm
                        if ((modulo100 == 0 && year % 400 == 0) || (modulo100 != 0 && year % LEAP_STEP == 0)) {
                            //its a leap year
                            return day < 30;
                        } else {
                            return day < 29;
                        }
                    default:
                        break;
                    }
                }
            }
            return false;
        }

        public String getRegex() {
            return pattern.pattern();
        }
    }
}

Some useful notes:
- to enable the assertions (assert checks) you need to use -ea argument when running the tester. (In eclipse this is done by editing the Run/Debug configuration -> Arguments tab -> VM Arguments -> insert "-ea"
- the regex above is bounded to years 1800 to 2199
- you don't need to use ^ at the beginning and $ at the end to match only the whole date string. The String.matches takes care of that.
- make sure u check the valid and invalid cases and change them according the rules that you have.
- the "only whole string" version of each regex gives the same speed as the "normal" version (the one without ^ and $). If you see performance differences this is because java "gets used" to processing the same instructions so the time lowers. If you switch the lines where the "normal" and the "only whole string" version execute, you will see this proven.

Hope this helps someone!
Cheers,
Despot

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孤傲高冷的网名

5楼-- · 2019-01-03 15:57

Construct a SimpleDateFormat with the mask, and then call: SimpleDateFormat.parse(String s, ParsePosition p)

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闹够了就滚

6楼-- · 2019-01-03 15:59

This will do it regex: "^((19|20)\\d\\d)-(0?[1-9]|1[012])-(0?[1-9]|[12][0-9]|3[01])$" This will take care of valid formats and valid dates. It will not validate the correct days of the month i.e. leap year.

String regex = "^((19|20)\\d\\d)-(0?[1-9]|1[012])-(0?[1-9]|[12][0-9]|3[01])$";

Assert.assertTrue("Date: matched.", Pattern.matches(regex, "2011-1-1"));
Assert.assertFalse("Date (month): not matched.", Pattern.matches(regex, "2011-13-1"));

Good luck!

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Regex date format validation on Java

java.time

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