I find it curious that the most obvious way to create Date objects in Java has been deprecated and appears to have been "substituted" with a not so obvious to use lenient calendar.
How do you check that a date, given as a combination of day, month, and year, is a valid date?
For instance, 2008-02-31 (as in yyyy-mm-dd) would be an invalid date.
Key is df.setLenient(false);. This is more than enough for simple cases. If you are looking for a more robust (I doubt that) and/or alternate libraries like joda-time, then look at the answer by user "tardate"
final static String DATE_FORMAT = "dd-MM-yyyy";
public static boolean isDateValid(String date)
{
try {
DateFormat df = new SimpleDateFormat(DATE_FORMAT);
df.setLenient(false);
df.parse(date);
return true;
} catch (ParseException e) {
return false;
}
}
As shown by #Maglob, the basic approach is to test the conversion from string to date using SimpleDateFormat.parse. That will catch invalid day/month combinations like 2008-02-31.
However, in practice that is rarely enough since SimpleDateFormat.parse is exceedingly liberal. There are two behaviours you might be concerned with:
Invalid characters in the date string
Surprisingly, 2008-02-2x will "pass" as a valid date with locale format = "yyyy-MM-dd" for example. Even when isLenient==false.
Years: 2, 3 or 4 digits?
You may also want to enforce 4-digit years rather than allowing the default SimpleDateFormat behaviour (which will interpret "12-02-31" differently depending on whether your format was "yyyy-MM-dd" or "yy-MM-dd")
A Strict Solution with the Standard Library
So a complete string to date test could look like this: a combination of regex match, and then a forced date conversion. The trick with the regex is to make it locale-friendly.
Date parseDate(String maybeDate, String format, boolean lenient) {
Date date = null;
// test date string matches format structure using regex
// - weed out illegal characters and enforce 4-digit year
// - create the regex based on the local format string
String reFormat = Pattern.compile("d+|M+").matcher(Matcher.quoteReplacement(format)).replaceAll("\\\\d{1,2}");
reFormat = Pattern.compile("y+").matcher(reFormat).replaceAll("\\\\d{4}");
if ( Pattern.compile(reFormat).matcher(maybeDate).matches() ) {
// date string matches format structure,
// - now test it can be converted to a valid date
SimpleDateFormat sdf = (SimpleDateFormat)DateFormat.getDateInstance();
sdf.applyPattern(format);
sdf.setLenient(lenient);
try { date = sdf.parse(maybeDate); } catch (ParseException e) { }
}
return date;
}
// used like this:
Date date = parseDate( "21/5/2009", "d/M/yyyy", false);
Note that the regex assumes the format string contains only day, month, year, and separator characters. Aside from that, format can be in any locale format: "d/MM/yy", "yyyy-MM-dd", and so on. The format string for the current locale could be obtained like this:
Locale locale = Locale.getDefault();
SimpleDateFormat sdf = (SimpleDateFormat)DateFormat.getDateInstance(DateFormat.SHORT, locale );
String format = sdf.toPattern();
Joda Time - Better Alternative?
I've been hearing about joda time recently and thought I'd compare. Two points:
Seems better at being strict about invalid characters in the date string, unlike SimpleDateFormat
Can't see a way to enforce 4-digit years with it yet (but I guess you could create your own DateTimeFormatter for this purpose)
It's quite simple to use:
import org.joda.time.format.*;
import org.joda.time.DateTime;
org.joda.time.DateTime parseDate(String maybeDate, String format) {
org.joda.time.DateTime date = null;
try {
DateTimeFormatter fmt = DateTimeFormat.forPattern(format);
date = fmt.parseDateTime(maybeDate);
} catch (Exception e) { }
return date;
}
tl;dr
Use the strict mode on java.time.DateTimeFormatter to parse a LocalDate. Trap for the DateTimeParseException.
LocalDate.parse( // Represent a date-only value, without time-of-day and without time zone.
"31/02/2000" , // Input string.
DateTimeFormatter // Define a formatting pattern to match your input string.
.ofPattern ( "dd/MM/uuuu" )
.withResolverStyle ( ResolverStyle.STRICT ) // Specify leniency in tolerating questionable inputs.
)
After parsing, you might check for reasonable value. For example, a birth date within last one hundred years.
birthDate.isAfter( LocalDate.now().minusYears( 100 ) )
Avoid legacy date-time classes
Avoid using the troublesome old date-time classes shipped with the earliest versions of Java. Now supplanted by the java.time classes.
LocalDate & DateTimeFormatter & ResolverStyle
The LocalDate class represents a date-only value without time-of-day and without time zone.
String input = "31/02/2000";
DateTimeFormatter f = DateTimeFormatter.ofPattern ( "dd/MM/uuuu" );
try {
LocalDate ld = LocalDate.parse ( input , f );
System.out.println ( "ld: " + ld );
} catch ( DateTimeParseException e ) {
System.out.println ( "ERROR: " + e );
}
The java.time.DateTimeFormatter class can be set to parse strings with any of three leniency modes defined in the ResolverStyle enum. We insert a line into the above code to try each of the modes.
f = f.withResolverStyle ( ResolverStyle.LENIENT );
The results:
ResolverStyle.LENIENTld: 2000-03-02
ResolverStyle.SMARTld: 2000-02-29
ResolverStyle.STRICTERROR: java.time.format.DateTimeParseException: Text '31/02/2000' could not be parsed: Invalid date 'FEBRUARY 31'
We can see that in ResolverStyle.LENIENT mode, the invalid date is moved forward an equivalent number of days. In ResolverStyle.SMART mode (the default), a logical decision is made to keep the date within the month and going with the last possible day of the month, Feb 29 in a leap year, as there is no 31st day in that month. The ResolverStyle.STRICT mode throws an exception complaining that there is no such date.
All three of these are reasonable depending on your business problem and policies. Sounds like in your case you want the strict mode to reject the invalid date rather than adjust it.
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.
You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.
Where to obtain the java.time classes?
Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
Java 9 adds some minor features and fixes.
Java SE 6 and Java SE 7
Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
Android
Later versions of Android bundle implementations of the java.time classes.
For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.
You can use SimpleDateFormat
For example something like:
boolean isLegalDate(String s) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
sdf.setLenient(false);
return sdf.parse(s, new ParsePosition(0)) != null;
}
The current way is to use the calendar class. It has the setLenient method that will validate the date and throw and exception if it is out of range as in your example.
Forgot to add:
If you get a calendar instance and set the time using your date, this is how you get the validation.
Calendar cal = Calendar.getInstance();
cal.setLenient(false);
cal.setTime(yourDate);
try {
cal.getTime();
}
catch (Exception e) {
System.out.println("Invalid date");
}
java.time
With the Date and Time API (java.time classes) built into Java 8 and later, you can use the LocalDate class.
public static boolean isDateValid(int year, int month, int day) {
try {
LocalDate.of(year, month, day);
} catch (DateTimeException e) {
return false;
}
return true;
}
Building on Aravind's answer to fix the problem pointed out by ceklock in his comment, I added a method to verify that the dateString doesn't contain any invalid character.
Here is how I do:
private boolean isDateCorrect(String dateString) {
try {
Date date = mDateFormatter.parse(dateString);
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
return matchesOurDatePattern(dateString); //added my method
}
catch (ParseException e) {
return false;
}
}
/**
* This will check if the provided string matches our date format
* #param dateString
* #return true if the passed string matches format 2014-1-15 (YYYY-MM-dd)
*/
private boolean matchesDatePattern(String dateString) {
return dateString.matches("^\\d+\\-\\d+\\-\\d+");
}
An alternative strict solution using the standard library is to perform the following:
1) Create a strict SimpleDateFormat using your pattern
2) Attempt to parse the user entered value using the format object
3) If successful, reformat the Date resulting from (2) using the same date format (from (1))
4) Compare the reformatted date against the original, user-entered value. If they're equal then the value entered strictly matches your pattern.
This way, you don't need to create complex regular expressions - in my case I needed to support all of SimpleDateFormat's pattern syntax, rather than be limited to certain types like just days, months and years.
I suggest you to use org.apache.commons.validator.GenericValidator class from apache.
GenericValidator.isDate(String value, String datePattern, boolean strict);
Note: strict - Whether or not to have an exact match of the datePattern.
I think the simpliest is just to convert a string into a date object and convert it back to a string. The given date string is fine if both strings still match.
public boolean isDateValid(String dateString, String pattern)
{
try
{
SimpleDateFormat sdf = new SimpleDateFormat(pattern);
if (sdf.format(sdf.parse(dateString)).equals(dateString))
return true;
}
catch (ParseException pe) {}
return false;
}
Assuming that both of those are Strings (otherwise they'd already be valid Dates), here's one way:
package cruft;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DateValidator
{
private static final DateFormat DEFAULT_FORMATTER;
static
{
DEFAULT_FORMATTER = new SimpleDateFormat("dd-MM-yyyy");
DEFAULT_FORMATTER.setLenient(false);
}
public static void main(String[] args)
{
for (String dateString : args)
{
try
{
System.out.println("arg: " + dateString + " date: " + convertDateString(dateString));
}
catch (ParseException e)
{
System.out.println("could not parse " + dateString);
}
}
}
public static Date convertDateString(String dateString) throws ParseException
{
return DEFAULT_FORMATTER.parse(dateString);
}
}
Here's the output I get:
java cruft.DateValidator 32-11-2010 31-02-2010 04-01-2011
could not parse 32-11-2010
could not parse 31-02-2010
arg: 04-01-2011 date: Tue Jan 04 00:00:00 EST 2011
Process finished with exit code 0
As you can see, it does handle both of your cases nicely.
This is working great for me. Approach suggested above by Ben.
private static boolean isDateValid(String s) {
SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
try {
Date d = asDate(s);
if (sdf.format(d).equals(s)) {
return true;
} else {
return false;
}
} catch (ParseException e) {
return false;
}
}
looks like SimpleDateFormat is not checking the pattern strictly even after setLenient(false); method is applied on it, so i have used below method to validate if the date inputted is valid date or not as per supplied pattern.
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
public boolean isValidFormat(String dateString, String pattern) {
boolean valid = true;
DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
try {
formatter.parse(dateString);
} catch (DateTimeParseException e) {
valid = false;
}
return valid;
}
Two comments on the use of SimpleDateFormat.
it should be declared as a static instance
if declared as static access should be synchronized as it is not thread safe
IME that is better that instantiating an instance for each parse of a date.
Above methods of date parsing are nice , i just added new check in existing methods that double check the converted date with original date using formater, so it works for almost each case as i verified. e.g. 02/29/2013 is invalid date.
Given function parse the date according to current acceptable date formats. It returns true if date is not parsed successfully.
public final boolean validateDateFormat(final String date) {
String[] formatStrings = {"MM/dd/yyyy"};
boolean isInvalidFormat = false;
Date dateObj;
for (String formatString : formatStrings) {
try {
SimpleDateFormat sdf = (SimpleDateFormat) DateFormat.getDateInstance();
sdf.applyPattern(formatString);
sdf.setLenient(false);
dateObj = sdf.parse(date);
System.out.println(dateObj);
if (date.equals(sdf.format(dateObj))) {
isInvalidFormat = false;
break;
}
} catch (ParseException e) {
isInvalidFormat = true;
}
}
return isInvalidFormat;
}
Here's what I did for Node environment using no external libraries:
Date.prototype.yyyymmdd = function() {
var yyyy = this.getFullYear().toString();
var mm = (this.getMonth()+1).toString(); // getMonth() is zero-based
var dd = this.getDate().toString();
return zeroPad([yyyy, mm, dd].join('-'));
};
function zeroPad(date_string) {
var dt = date_string.split('-');
return dt[0] + '-' + (dt[1][1]?dt[1]:"0"+dt[1][0]) + '-' + (dt[2][1]?dt[2]:"0"+dt[2][0]);
}
function isDateCorrect(in_string) {
if (!matchesDatePattern) return false;
in_string = zeroPad(in_string);
try {
var idate = new Date(in_string);
var out_string = idate.yyyymmdd();
return in_string == out_string;
} catch(err) {
return false;
}
function matchesDatePattern(date_string) {
var dateFormat = /[0-9]+-[0-9]+-[0-9]+/;
return dateFormat.test(date_string);
}
}
And here is how to use it:
isDateCorrect('2014-02-23')
true
// to return valid days of month, according to month and year
int returnDaysofMonth(int month, int year) {
int daysInMonth;
boolean leapYear;
leapYear = checkLeap(year);
if (month == 4 || month == 6 || month == 9 || month == 11)
daysInMonth = 30;
else if (month == 2)
daysInMonth = (leapYear) ? 29 : 28;
else
daysInMonth = 31;
return daysInMonth;
}
// to check a year is leap or not
private boolean checkLeap(int year) {
Calendar cal = Calendar.getInstance();
cal.set(Calendar.YEAR, year);
return cal.getActualMaximum(Calendar.DAY_OF_YEAR) > 365;
}
Here is I would check the date format:
public static boolean checkFormat(String dateTimeString) {
return dateTimeString.matches("^\\d{4}-\\d{2}-\\d{2}") || dateTimeString.matches("^\\d{4}-\\d{2}-\\d{2}\\s\\d{2}:\\d{2}:\\d{2}")
|| dateTimeString.matches("^\\d{4}-\\d{2}-\\d{2}T\\d{2}:\\d{2}:\\d{2}") || dateTimeString
.matches("^\\d{4}-\\d{2}-\\d{2}T\\d{2}:\\d{2}:\\d{2}Z") ||
dateTimeString.matches("^\\d{4}-\\d{2}-\\d{2}\\s\\d{2}:\\d{2}:\\d{2}Z");
}
public static String detectDateFormat(String inputDate, String requiredFormat) {
String tempDate = inputDate.replace("/", "").replace("-", "").replace(" ", "");
String dateFormat;
if (tempDate.matches("([0-12]{2})([0-31]{2})([0-9]{4})")) {
dateFormat = "MMddyyyy";
} else if (tempDate.matches("([0-31]{2})([0-12]{2})([0-9]{4})")) {
dateFormat = "ddMMyyyy";
} else if (tempDate.matches("([0-9]{4})([0-12]{2})([0-31]{2})")) {
dateFormat = "yyyyMMdd";
} else if (tempDate.matches("([0-9]{4})([0-31]{2})([0-12]{2})")) {
dateFormat = "yyyyddMM";
} else if (tempDate.matches("([0-31]{2})([a-z]{3})([0-9]{4})")) {
dateFormat = "ddMMMyyyy";
} else if (tempDate.matches("([a-z]{3})([0-31]{2})([0-9]{4})")) {
dateFormat = "MMMddyyyy";
} else if (tempDate.matches("([0-9]{4})([a-z]{3})([0-31]{2})")) {
dateFormat = "yyyyMMMdd";
} else if (tempDate.matches("([0-9]{4})([0-31]{2})([a-z]{3})")) {
dateFormat = "yyyyddMMM";
} else {
return "Pattern Not Added";
//add your required regex
}
try {
String formattedDate = new SimpleDateFormat(requiredFormat, Locale.ENGLISH).format(new SimpleDateFormat(dateFormat).parse(tempDate));
return formattedDate;
} catch (Exception e) {
//
return "";
}
}
setLenient to false if you like a strict validation
public boolean isThisDateValid(String dateToValidate, String dateFromat){
if(dateToValidate == null){
return false;
}
SimpleDateFormat sdf = new SimpleDateFormat(dateFromat);
sdf.setLenient(false);
try {
//if not valid, it will throw ParseException
Date date = sdf.parse(dateToValidate);
System.out.println(date);
} catch (ParseException e) {
e.printStackTrace();
return false;
}
return true;
}
With 'legacy' date format, we can format the result and compare it back to the source.
public boolean isValidFormat(String source, String pattern) {
SimpleDateFormat sd = new SimpleDateFormat(pattern);
sd.setLenient(false);
try {
Date date = sd.parse(source);
return date != null && sd.format(date).equals(source);
} catch (Exception e) {
return false;
}
}
This execerpt says 'false' to source=01.01.04 with pattern '01.01.2004'
We can use the org.apache.commons.validator.GenericValidator's method directly without adding the whole library:
public static boolean isValidDate(String value, String datePattern, boolean strict) {
if (value == null
|| datePattern == null
|| datePattern.length() <= 0) {
return false;
}
SimpleDateFormat formatter = new SimpleDateFormat(datePattern, Locale.ENGLISH);
formatter.setLenient(false);
try {
formatter.parse(value);
} catch(ParseException e) {
return false;
}
if (strict && (datePattern.length() != value.length())) {
return false;
}
return true;
}
A simple and elegant way for Android developers (Java 8 not required):
// month value is 1-based. e.g., 1 for January.
public static boolean isDateValid(int year, int month, int day) {
Calendar calendar = Calendar.getInstance();
try {
calendar.setLenient(false);
calendar.set(year, month-1, day);
calendar.getTime();
return true;
} catch (Exception e) {
return false;
}
}
Below code works with dd/MM/yyyy format and can be used to check NotNull,NotEmpty as well.
public static boolean validateJavaDate(String strDate) {
if (strDate != null && !strDate.isEmpty() && !strDate.equalsIgnoreCase(" ")) {
{
SimpleDateFormat date = new SimpleDateFormat("dd/MM/yyyy");
date.setLenient(false);
try {
Date javaDate = date.parse(strDate);
System.out.println(strDate + " Valid Date format");
}
catch (ParseException e) {
System.out.println(strDate + " Invalid Date format");
return false;
}
return true;
}
} else {
System.out.println(strDate + "----> Date is Null/Empty");
return false;
}
}
My application queries a SQLite DateTime string and I'm trying to write a single method than I can use across my application so that DateTime timestamps are formatted consistently. So far I have,
public class DateTimeUtils {
public static String formatDueDate(String queryResponse) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss z", Locale.US);
Date result = new Date();
try {
result = sdf.parse(queryResponse);
} catch (ParseException e) {
e.printStackTrace();
}
return result.toString();
}
}
Which is used in a situations such as
taskViewHolder.mDue.setText(formatDueDate(task.getDue().toString()));
I'd like the output to look like June 27, 20015, 5:30PM
The raw datetime String takes the form: 2015-08-10T17:28:00.000-04:00
My problems are currently the resulting timestamp format is incorrect and instead looks like Sun Aug 02 17:29:03 EDT 2015 and instead of parsing the inputted timestamp, just returns the current datetime.
I believe this is because my formatting is actually throwing an exception and i'm just returning the current Date() object. What should I change so that the datetime string is parsed correctly?
Well, since you're creating the Date object outside the try block, you're right, if there is a parsing error, the current date will return. SimpleDateFormat does that work for you in the parse method. You could reduce the possibility of the current date returning by assigning the Date variable to null instead of instantiating a new object.
If you already get an correct Date class, maybe you can generator your special format by Calendar class and StringBuilder class.
Like below:
String[] monthString = new String[12];
if (monthString[0] == null) {
// Get month string by android locale
// The String will like Jule or May ...
Map<String, Integer> months = Calendar.getInstance().getDisplayNames(Calendar.MONTH, Calendar.LONG, getResources().getConfiguration().locale);
for (int i = 0; i < 12; i++) {
for (String month : months.keySet()) {
if (i == months.get(month).intValue()) {
monthString[i] = month;
months.remove(month);
break;
}
}
}
}
Calendar calendar=Calendar.getInstance();
calendar.setTime(result);
StringBuilder sb=new StringBuilder();
sb.append(monthString[calendar.get(Calendar.MONTH)]);
//spec your format string...
Hope this can help you.
I have a string holding a start time and an end time in this format 8:30AM - 9:30PM I want to be able to strip out the AM - and the PM and convert all the times to 24 hour format so 9:30PM would really be 21:30 and also have both the times stored in 2 different variables, I know how to strip the string into substrings but Im not sure about the conversion, this is what I have so far. the time variable starts out holding 8:30AM - 9:30PM.
String time = strLine.substring(85, 110).trim();
//time is "8:30AM - 9:30PM"
String startTime;
startTime = time.substring(0, 7).trim();
//startTime is "8:30AM"
String endTime;
endTime = time.substring(9).trim();
//endTime "9:30AM"
Working code (considering that you managed to split the Strings):
public class App {
public static void main(String[] args) {
try {
System.out.println(convertTo24HoursFormat("12:00AM")); // 00:00
System.out.println(convertTo24HoursFormat("12:00PM")); // 12:00
System.out.println(convertTo24HoursFormat("11:59PM")); // 23:59
System.out.println(convertTo24HoursFormat("9:30PM")); // 21:30
} catch (ParseException ex) {
Logger.getLogger(App.class.getName()).log(Level.SEVERE, null, ex);
}
}
// Replace with KK:mma if you want 0-11 interval
private static final DateFormat TWELVE_TF = new SimpleDateFormat("hh:mma");
// Replace with kk:mm if you want 1-24 interval
private static final DateFormat TWENTY_FOUR_TF = new SimpleDateFormat("HH:mm");
public static String convertTo24HoursFormat(String twelveHourTime)
throws ParseException {
return TWENTY_FOUR_TF.format(
TWELVE_TF.parse(twelveHourTime));
}
}
Now that I think about it, SimpleDateFormat, H h K k can be confusing.
Cheers.
You need to use: SimpleDateFormat
And can refer this tutorial: Formatting hour using SimpleDateFormat
Example:
//create Date object
Date date = new Date();
//formatting hour in h (1-12 in AM/PM) format like 1, 2..12.
String strDateFormat = "h";
SimpleDateFormat sdf = new SimpleDateFormat(strDateFormat);
System.out.println("hour in h format : " + sdf.format(date));
I wouldn't reinvent the wheel (unless you are doing this as a school project or some such).
Just get a date object out of your time stamp and then you can generate whatever format you want with this: SimpleDateFormat
[edited to address your specific request]
if you absolutely need to work from your own unique strings, then you'll do something like this (I don't know exactly what your strings look like... you're using offsets like 85, which means nothing out of context).
I didn't check this for bugs, but this is approximately what you want...
myStr = timestampString.toLowerCase(); //something like 8:30am
boolean add12 = (myStr.indexOf("pm") != -1)?true:false;
//convert hour to int
int hour = Integer.parseInt(myStr.split(":")[0]);
int minutes = Integer.parseInt( myStr.split(":")[1].replaceAll("\\D+","").replaceAll("^0+","") ); //get the letters out of the minute part and get a number out of that, also, strip out leading zeros
int militaryTime = hour + (add12)? 12:0;
if(!add12 && militaryTime == 12)
militaryTime = 0; //account for 12am
//dont' forget to add the leading zeros back in as you assemble your string
With Joda Time, the code looks like:
DateTimeFormatter formatter12 = DateTimeFormat.forPattern("K:mma");
DateTime begin = formatter12.parseDateTime(beginTime);
DateTime end = formatter12.parseDateTime(endTime);
DateTimeFormatter formatter24 = DateTimeFormat.forPattern("k:mma");
String begin24 = formatter24.print(begin);
String end24 = formatter24.print(end);
I should like to contribute the modern answer
DateTimeFormatter twelveHourFormatter = DateTimeFormatter.ofPattern("h:mma", Locale.ENGLISH);
String time = "8:30AM - 9:30PM";
String[] times = time.split(" - ");
LocalTime start = LocalTime.parse(times[0], twelveHourFormatter);
System.out.println(start.toString());
LocalTime end = LocalTime.parse(times[1], twelveHourFormatter);
System.out.println(end.toString());
This prints:
08:30
21:30
I am using java.time, the modern Java date and time API. The SimpleDateFormat class used in many of the other answers is long outdated and was always troublesome. java.time is so much nicer to work with than the date-time classes from the 1990’s. A LocalTime is a time of day without a date (and without time zone), so suits your need much better than an old-fashioned Date.
Link: Oracle tutorial: Date Time explaining how to use java.time.
24 hour time adds 12 to any time greater than 12pm so that 1pm is 13 and so on until 24 or 12am. Here is the sudo code:
if(hour <= 12)
{
hour = hour + 12;
}
All the below lines will works when
String str="07:05:45PM";
and when you call timeConversion(str) and want to convert to 24 hours format..
public class TimeConversion {
private static final DateFormat TWELVE_TF = new SimpleDateFormat("hh:mm:ssa");
private static final DateFormat TWENTY_FOUR_TF = new SimpleDateFormat("HH:mm:ss");
static String timeConversion(String s) {
String str = null;
try {
str= TWENTY_FOUR_TF.format(
TWELVE_TF.parse(s));
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return str;
}
public static void main(String[] args) throws ParseException {
String str="07:05:45PM";
System.out.println(timeConversion(str));
}
}
I'm trying to figure out a "simple" way of parsing a String into a Date Object.
The String can be either yyyyMMdd, yyyyMMddHHmm or yyyyMMddHHmmSS.
Currently, I'm looking at the length of the String, and creating a DateParser depending on the length. Is there a more elegant way of doing this?
Or you can pad your string with zeros:
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmSS") {
#Override
public Date parse(String s) throws ParseException {
return super.parse((s + "000000").substring(0, 14));
}
};
System.out.println(sdf.format(sdf.parse("20110711182405")));
System.out.println(sdf.format(sdf.parse("201107111824")));
System.out.println(sdf.format(sdf.parse("20110711")));
I would do as you are, looking at the length of the string, and creating an appropriate SimpleDateFormat instance.
SimpleDateFormat getFormatFor( String dateString ){
if ( dateString.length() == 8 ) return new SimpleDateFormat("yyyyMMdd");
if ( dateString.length() == 14 ) return new SimpleDateFormat("yyyyMMddHHmmss");
// you got a bad input...
}
NB these are not thread-safe, so you should create a new one each time.
I would use a SimpleDateFormat class, and populate the format pattern based on the length of the string. That'll work fine unless you one day have strings of the same length.
Using the examples from your question:
Formatting 11th July 2011:
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
Date parsedDate = dateFormat.parse("20110711");
Formatting 11th July 2011 1340hrs:
dateFormat = new SimpleDateFormat("yyyyMMddHHmm");
parsedDate = dateFormat.parse("201107111340");
Formatting 11th July 2011 1340hrs 10 seconds:
(NB. small s for seconds, capital S is for Milliseconds!)
dateFormat = new SimpleDateFormat("yyyyMMddHHmmss");
parsedDate = dateFormat.parse("20110711134010");
See the hyperlink for the full list of format pattern letters.
You could still used "specialized" parsers (as you suggested) and chain them:
For instance, you can still have a DateHourMinSecParser (for yyyyMMddHHmmSS), a DateHourMinParser (for yyyyMMddHHmm) and a DateParser (for yyyyMMdd) all of them implementing the same interface:
public interface GenericDateParser {
Date parseDate(String input) throws IllegalArgumentException;
}
e.g.
public class DateHourMinSecParser implements GenericDateParser {
...
public Date parseDate(String input) throws IllegalArgumentException {
...
}
}
but each one of these classes would actually take a parameter another GenericDateParser -- the idea being that each parser would try first to parse the date itself, if the parsing (or some internal checks -- e.g. string length) fails it would then pass it to the next parser in chain until either there are no more parsers in the chain (in which case it would throw an exception, or one of the members in the chain would return a value):
public class DateHourMinSecParser implements GenericDateParser {
private GenericDateParser chained;
public DateHourMinSecParser(GenericDateParser chained) {
this.chained = chained;
}
public Date parseDate(String input) throws IllegalArgumentException {
if( !internalChecks() ) { //chain it up
if( chained == null ) throw new IllegalArgumentException( "Don't know how to parse " + input);
}
//internal checks passed so try to parse it and return a Date or throw exception
...
}
}
and you would initialize them:
GenericDateParser p = new DateHourMinSecParser( new DateHourMinParser(new DateParser(null)) );
and then just use the top level one:
Date d = p.parse( '20110126' );
You can use a DateFormatter to parse the Date from the string.
import java.util.*;
import java.text.*;
public class StringToDate
{
public static void main(String[] args)
{
try
{
String str_date="11-June-07";
DateFormat formatter ;
Date date ;
formatter = new SimpleDateFormat("yyyy-MM-dd");
date = (Date)formatter.parse(str_date);
}
catch (ParseException e)
{
System.out.println("Exception :"+e);
}
}
}
You can change the pattern however you like to reflect your needs.