I have this code copied from one of questions from SO:
public static String getCurrentTimeStamp() {
SimpleDateFormat sdfDate = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date now = new Date();
String strDate = sdfDate.format(now);
return strDate;
}
I want to get only the system time and NOT the date. Then I must change second line of code to:
SimpleDateFormat sdfDate = new SimpleDateFormat(" HH:mm:ss") ;
Then, DATE() must get the current time. Clear upto this point but I can't understand the format() function used.
I mean cant we simply output variable now instead of strdate?
Is it just because that the return type of function getCurrentTimeStamp() is String?
Please clarify and if there is any other simpler and one line code for getting system time alone, do share.
I mean cant we simply output variable now instead of strdate.
Well you could return now.toString() - but that will use the format that Date.toString() happens to choose, whereas you want a specific format. The point of the SimpleDateFormat object in this case is to convert a Date (which is a point in time, without reference to any particular calendar or time zone) into a String, applying an appropriate time zone, calendar system, and text format (in your case HH:mm:ss).
You can still simplify your method somewhat though, by removing the local variables (which are each only used once):
public static String getCurrentTimeStamp() {
return new SimpleDateFormat("HH:mm:ss").format(new Date());
}
Or maybe you'd find it more readable to keep the variable for the date format, but not the date and the return value:
public static String getCurrentTimeStamp() {
DateFormat format = new SimpleDateFormat("HH:mm:ss");
return format.format(new Date());
}
Personally I'd recommend using Joda Time instead, mind you - it's a much nicer date/time API, and its formatted are thread-safe so you could easily keep a reference to a single formatting object.
public static String getCurrentTimeStampwithTimeOnly() {
return new SimpleDateFormat("HH:mm:ss").format(new Date());
}
Helps you to do this.
you can call this line any time
Date now = new Date();
The now variable will contain the current timestamp
The format function just generates a String from this timestamp
also take a look at the Calendar class ( Calendar.getInstance())
Related
I am working on a project where I am comparing the date and time in a custom Comparator. I actually concatenated the date with date and time. When I debugged the issue, I realized that time is not getting sorted. Here is the snippet of my code from my Comparator.
Date dateObject1= new Date();
Date dateObject2 = new Date();
try {
dateObject1 = sdf.parse(date1 + "T" + time1);
dateObject2 = sdf.parse(date2 + "T" + time2);
} catch (Exception e) { }
if (dateObject1.compareTo(dateObject2) > 0)
return 1;
else if (dateObject1.compareTo(dateObject2) < 0)
return -1;
else
return 0;
Test cases:
1. date1 - 2019-12-13 , date2 - 2019-12-13
time1 - 08:00:00, time2 - 12:00:00
When i debugged the issue I found it's returning 0 for the above test case. I am not sure why it's happening but I intent to return -1 such that it's sorted in ascending order.
Please advice.
Your problem is here
} catch (Exception e) { }
You initialize your 2 dates, both of which get initialized to the current time (System.currentTimeMillis()).
Date dateObject1= new Date();
Date dateObject2 = new Date();
Your parsing then fails, but you swallow the exception so you never noticed it.
Then you try to sort two dates which are either exactly same, or separated by a couple of milliseconds, but are certainly unrelated to the actual timestamps that you're trying to sort.
Check the exception, fix the parsing, and then it will work.
java.time and Comparator.comparing … thenComparing
I don’t know what your Java version is. The following snippet works on Java 8 and above. The most important ideas can be applied on Java 6 and 7 too.
List<MyObject> listToBeSorted = Arrays.asList(
new MyObject("2019-12-12", "11:53:50"),
new MyObject("2019-12-11", "13:07:05"),
new MyObject("2019-12-13", "05:02:16"),
new MyObject("2019-12-11", "09:54:57"),
new MyObject("2019-12-12", "05:53:52"),
new MyObject("2019-12-13", "06:56:08"),
new MyObject("2019-12-12", "02:31:55"),
new MyObject("2019-12-11", "09:28:16"),
new MyObject("2019-12-11", "20:58:55"));
Comparator<MyObject> cmpr = Comparator.comparing(MyObject::getDate)
.thenComparing(MyObject::getTime);
listToBeSorted.sort(cmpr);
listToBeSorted.forEach(System.out::println);
Output is:
MyObject [date=2019-12-11, time=09:28:16]
MyObject [date=2019-12-11, time=09:54:57]
MyObject [date=2019-12-11, time=13:07:05]
MyObject [date=2019-12-11, time=20:58:55]
MyObject [date=2019-12-12, time=02:31:55]
MyObject [date=2019-12-12, time=05:53:52]
MyObject [date=2019-12-12, time=11:53:50]
MyObject [date=2019-12-13, time=05:02:16]
MyObject [date=2019-12-13, time=06:56:08]
You will observe that the objects have been sorted by date and objects with the same date also by time. Here is the MyObject class that I used:
public class MyObject {
LocalDate date;
LocalTime time;
public MyObject(String dateString, String timeString) {
date = LocalDate.parse(dateString);
time = LocalTime.parse(timeString);
}
public LocalDate getDate() {
return date;
}
public LocalTime getTime() {
return time;
}
#Override
public String toString() {
return "MyObject [date=" + date + ", time=" + time + "]";
}
}
The two key messages are:
Don’t keep your dates and times as strings in your objects. Keep proper date and time objects. It may require parsing strings when you build your objects, but everything else gets noticeably easier.
Don’t use Date and SimpleDateFormat at all. Use classes from java.time, the modern Java date and time API. In this case LocalDate and LocalTime. The SimpleDateFormat and Date classes are poorly designed and long outdated, the former in particular notoriously troublesome. The modern API is so much nicer to work with.
The advantage of the Comparator methods comparing and thenComparing is not so much that code gets considerably shorter. The really important gain is that writing comparators in this style is much less error prone, and the code reads more naturally.
What went wrong in your code?
The problem is in the line that you posted in a comment:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
This formatter only parses the date from each string and ignores the time. It’s one of many confusing traits of SimpleDateFormat that it is happy to parse only a part of the string and doesn’t draw our attention to the fact that some of the text is ignored — in this case the T and the entire time.
Link
Oracle tutorial: Date Time explaining how to use java.time.
Just return the value of the comparison since that is what you return anyway.
Date dateObject1= new Date();
Date dateObject2 = new Date();
try {
dateObject1 = sdf.parse(date1 + "T" + time1);
dateObject2 = sdf.parse(date2 + "T" + time2);
} catch (Exception e) {
e.printStackTrace(); // always print these. They are there to help you.
}
return dateObject1.compareTo(dateObject2);
I have a private method which takes date in as String type and returns XMLGregorianCalendar object with specific format. This method is being invoked from various other methods within the same class.
The format defined as SimpleDateFormat which is same for every invocation. Below are the 2 versions of the method.
Version 1:
private XMLGregorianCalendar getXmlGregorianCalendar(final String strDt) throws ParseException, DatatypeConfigurationException{
Date date = null;
// local variable dtFormat
DateFormat dtFormat = new SimpleDateFormat("yyyy-MM-dd-hh.mm.ss");
if (strDt != null) {
date = dtFormat.parse(strDt);
GregorianCalendar cal = new GregorianCalendar();
cal.setTime(date);
XMLGregorianCalendar xmlCal = DatatypeFactory.newInstance().newXMLGregorianCalendar(cal);
return xmlCal;
}else {
return DatatypeFactory.newInstance().newXMLGregorianCalendar(new GregorianCalendar());
}
}
Version 2:
// declare date format once, global variable
private DateFormat dtFormat = new SimpleDateFormat("yyyy-MM-dd-hh.mm.ss");
// getter setter for dtFormat
private XMLGregorianCalendar getXmlGregorianCalendar(final String strDt) throws ParseException, DatatypeConfigurationException{
Date date = null;
if (strDt != null) {
date = this.dtFormat.parse(strDt); // of course, getDtFormat() can be used
GregorianCalendar cal = new GregorianCalendar();
cal.setTime(date);
XMLGregorianCalendar xmlCal = DatatypeFactory.newInstance().newXMLGregorianCalendar(cal);
return xmlCal;
}else {
return DatatypeFactory.newInstance().newXMLGregorianCalendar(new GregorianCalendar());
}
}
Version 1 vs Version 2. Which has better performance?
Note: The enclosed class is annotated as #Component and involved in creating response for my web service.
SimpleDateFormat is not thread-safe, so that would be something to consider. Performance has little to do with this question, unless you really don't have any other performance hotspots (which would be surprising).
You can however use a ThreadLocal SimpleDateFormat, but remember that ThreadLocals have their own issues, and it probably doesn't really matter.
If that SimpleDateFormat is a constant, you can make it static final and it would improve your performance just a little bit. But you should be aware of the concept of static fields in classes. static fields are allocated once in memory for all instances of your #Component class. So if this cannot creating a bug in your code, it's better to define it as a constant using static final keywords.
I need to check if a given timestamp is today. I am using Joda-Time. Is there a method or a simple way to check this? What Joda-Time class is better suited for this? LocalDate? DateTime?
The date can be compared by single statement so why you need a special function.
when dateTimeis an object of DateTime()
if((dateTime.toLocalDate()).equals(new LocalDate()))
when date is an object of java.util.date
if((new DateTime(date).toLocalDate()).equals(new LocalDate()))
What Joda-time class is better suited for this? LocalDate? DateTime?
The understanding that you need to know what is LocalDate and DateTime.
LocalDate() is an immutable datetime class representing a date without a
time zone. So is not having a time part.
DateTime() is the standard implementation of an unmodifiable datetime
class. Its having all the attributes of the Date, which includes
date, time and timezone.
So if you need to compare both the date and time better go with datetime, if you just need to check the date you must use localDate because the datetime will produce a false if an .equal operator is used, unless the time including the seconds part are same for both the objects.
Here are some simple methods to check if a DateTime is today, tomorrow or yesterday:
public boolean isToday(DateTime time) {
return LocalDate.now().compareTo(new LocalDate(time)) == 0;
}
public boolean isTomorrow(DateTime time) {
return LocalDate.now().plusDays(1).compareTo(new LocalDate(time)) == 0;
}
public boolean isYesterday(DateTime time) {
return LocalDate.now().minusDays(1).compareTo(new LocalDate(time)) == 0;
}
One possibility is to create an interval covering the whole day in question, and then check if the various timestamps are contained in this interval.
Constructing the initial interval could look like:
Interval today = new Interval(DateTime.now().withTimeAtStartOfDay(), Days.ONE);
Then the timestamps could be checked like so:
today.contains(DateTime.now()); // True
today.contains(DateTime.now().minusDays(1)); // False
today.contains(DateTime.now().plusDays(1)); // False
today.contains(someOtherTimeStamp.toDateTime()); // And so on...
The recommended way to do this would be:
DateTime midnightToday = DateTime.now().withTimeAtStartOfDay();
DateTime myDateTime = <whatever>;
if(myDateTime.isAfter(midnightToday)) {
}
I think you need Joda 2.5 to do this, but that should do the trick.
I like #JustinMorris's answer. But I found this even better:
public static boolean isToday(DateTime time) {
return LocalDate.now().equals(new LocalDate(time));
}
public static boolean isTomorrow(DateTime time) {
return LocalDate.now().plusDays(1).equals(new LocalDate(time));
}
public static boolean isYesterday(DateTime time) {
return LocalDate.now().minusDays(1).equals(new LocalDate(time));
}
AFAIK there is no direct method available by which you can check the Date is Today Date or not.
The simplest approach will be constructing two DateTime one with the Timestamp, and another with today Date and then comparing day from dayOfYear() and year from year() but do remember whether both Date are in UTC or in Local Time Zone.
A small sample,
DateTime date = new DateTime(TimeStamp);
DateTime todayDate = new DateTime();
if(date.dayOfYear().get() == todayDate.dayOfYear().get() && date.year().get() == todayDate.year().get())
{
System.out.println("Date is today date");
}
Joda time actually have a method for this:
DateUtils#isToday(ReadablePartial);
DateUtils#isToday(ReadableInstant);
Simplest way I've found:
public boolean isToday(DateTime dateTime) {
return dateTime.withTimeAtStartOfDay().getMillis() ==
new DateTime().withTimeAtStartOfDay().getMillis();
}
The javadoc for SimpleDateFormat states that SimpleDateFormat is not synchronized.
"Date formats are not synchronized. It
is recommended to create separate
format instances for each thread. If
multiple threads access a format
concurrently, it must be synchronized
externally."
But what is the best approach to using an instance of SimpleDateFormat in a multi threaded environment. Here are a few options I have thought of, I have used options 1 and 2 in the past but I am curious to know if there are any better alternatives or which of these options would offer the best performance and concurrency.
Option 1: Create local instances when required
public String formatDate(Date d) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
return sdf.format(d);
}
Option 2: Create an instance of SimpleDateFormat as a class variable but synchronize access to it.
private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
public String formatDate(Date d) {
synchronized(sdf) {
return sdf.format(d);
}
}
Option 3: Create a ThreadLocal to store a different instance of SimpleDateFormat for each thread.
private ThreadLocal<SimpleDateFormat> tl = new ThreadLocal<SimpleDateFormat>();
public String formatDate(Date d) {
SimpleDateFormat sdf = tl.get();
if(sdf == null) {
sdf = new SimpleDateFormat("yyyy-MM-hh");
tl.set(sdf);
}
return sdf.format(d);
}
Creating SimpleDateFormat is expensive. Don't use this unless it's done seldom.
OK if you can live with a bit of blocking. Use if formatDate() is not used much.
Fastest option IF you reuse threads (thread pool). Uses more memory than 2. and has higher startup overhead.
For applications both 2. and 3. are viable options. Which is best for your case depends on your use case. Beware of premature optimization. Only do it if you believe this is an issue.
For libraries that would be used by 3rd party I'd use option 3.
The other option is Commons Lang FastDateFormat but you can only use it for date formatting and not parsing.
Unlike Joda, it can function as a drop-in replacement for formatting.
(Update: Since v3.3.2, FastDateFormat can produce a FastDateParser, which is a drop-in thread-safe replacement for SimpleDateFormat)
If you are using Java 8, you may want to use java.time.format.DateTimeFormatter:
This class is immutable and thread-safe.
e.g.:
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
String str = new java.util.Date().toInstant()
.atZone(ZoneId.systemDefault())
.format(formatter);
Commons Lang 3.x now has FastDateParser as well as FastDateFormat. It is thread safe and faster than SimpleDateFormat. It also uses the same format/parse pattern specifications as SimpleDateFormat.
Don't use SimpleDateFormat, use joda-time's DateTimeFormatter instead. It is a bit stricter in the parsing side and so isn't quite a drop in replacement for SimpleDateFormat, but joda-time is much more concurrent friendly in terms of safety and performance.
I would say, create a simple wrapper-class for SimpleDateFormat that synchronizes access to parse() and format() and can be used as a drop-in replacement. More foolproof than your option #2, less cumbersome than your option #3.
Seems like making SimpleDateFormat unsynchronized was a poor design decision on the part of the Java API designers; I doubt anyone expects format() and parse() to need to be synchronized.
Another option is to keep instances in a thread-safe queue:
import java.util.concurrent.ArrayBlockingQueue;
private static final int DATE_FORMAT_QUEUE_LEN = 4;
private static final String DATE_PATTERN = "yyyy-MM-dd HH:mm:ss";
private ArrayBlockingQueue<SimpleDateFormat> dateFormatQueue = new ArrayBlockingQueue<SimpleDateFormat>(DATE_FORMAT_QUEUE_LEN);
// thread-safe date time formatting
public String format(Date date) {
SimpleDateFormat fmt = dateFormatQueue.poll();
if (fmt == null) {
fmt = new SimpleDateFormat(DATE_PATTERN);
}
String text = fmt.format(date);
dateFormatQueue.offer(fmt);
return text;
}
public Date parse(String text) throws ParseException {
SimpleDateFormat fmt = dateFormatQueue.poll();
if (fmt == null) {
fmt = new SimpleDateFormat(DATE_PATTERN);
}
Date date = null;
try {
date = fmt.parse(text);
} finally {
dateFormatQueue.offer(fmt);
}
return date;
}
The size of dateFormatQueue should be something close to the estimated number of threads which can routinely call this function at the same time.
In the worst case where more threads than this number do actually use all the instances concurrently, some SimpleDateFormat instances will be created which cannot be returned to dateFormatQueue because it is full. This will not generate an error, it will just incur the penalty of creating some SimpleDateFormat which are used only once.
I just implemented this with Option 3, but made a few code changes:
ThreadLocal should usually be static
Seems cleaner to override initialValue() rather than test if (get() == null)
You may want to set locale and time zone unless you really want the default settings (defaults are very error prone with Java)
private static final ThreadLocal<SimpleDateFormat> tl = new ThreadLocal<SimpleDateFormat>() {
#Override
protected SimpleDateFormat initialValue() {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-hh", Locale.US);
sdf.setTimeZone(TimeZone.getTimeZone("America/Los_Angeles"));
return sdf;
}
};
public String formatDate(Date d) {
return tl.get().format(d);
}
Imagine your application has one thread. Why would you synchronize access to SimpleDataFormat variable then?
I have this situation where I am reading about 130K records containing dates stored as String fields. Some records contain blanks (nulls), some contain strings like this: 'dd-MMM-yy' and some contain this 'dd/MM/yyyy'.
I have written a method like this:
public Date parsedate(String date){
if(date !== null){
try{
1. create a SimpleDateFormat object using 'dd-MMM-yy' as the pattern
2. parse the date
3. return the parsed date
}catch(ParseException e){
try{
1. create a SimpleDateFormat object using 'dd/MM/yyy' as the pattern
2. parse the date
3. return parsed date
}catch(ParseException e){
return null
}
}
}else{
return null
}
}
So you may have already spotted the problem. I am using the try .. catch as part of my logic. It would be better is I can determine before hand that the String actually contains a parseable date in some format then attempt to parse it.
So, is there some API or library that can help with this? I do not mind writing several different Parse classes to handle the different formats and then creating a factory to select the correct6 one, but, how do I determine which one?
Thanks.
See Lazy Error Handling in Java for an overview of how to eliminate try/catch blocks using an Option type.
Functional Java is your friend.
In essence, what you want to do is to wrap the date parsing in a function that doesn't throw anything, but indicates in its return type whether parsing was successful or not. For example:
import fj.F; import fj.F2;
import fj.data.Option;
import java.text.SimpleDateFormat;
import java.text.ParseException;
import static fj.Function.curry;
import static fj.Option.some;
import static fj.Option.none;
...
F<String, F<String, Option<Date>>> parseDate =
curry(new F2<String, String, Option<Date>>() {
public Option<Date> f(String pattern, String s) {
try {
return some(new SimpleDateFormat(pattern).parse(s));
}
catch (ParseException e) {
return none();
}
}
});
OK, now you've a reusable date parser that doesn't throw anything, but indicates failure by returning a value of type Option.None. Here's how you use it:
import fj.data.List;
import static fj.data.Stream.stream;
import static fj.data.Option.isSome_;
....
public Option<Date> parseWithPatterns(String s, Stream<String> patterns) {
return stream(s).apply(patterns.map(parseDate)).find(isSome_());
}
That will give you the date parsed with the first pattern that matches, or a value of type Option.None, which is type-safe whereas null isn't.
If you're wondering what Stream is... it's a lazy list. This ensures that you ignore patterns after the first successful one. No need to do too much work.
Call your function like this:
for (Date d: parseWithPatterns(someString, stream("dd/MM/yyyy", "dd-MM-yyyy")) {
// Do something with the date here.
}
Or...
Option<Date> d = parseWithPatterns(someString,
stream("dd/MM/yyyy", "dd-MM-yyyy"));
if (d.isNone()) {
// Handle the case where neither pattern matches.
}
else {
// Do something with d.some()
}
Don't be too hard on yourself about using try-catch in logic: this is one of those situations where Java forces you to so there's not a lot you can do about it.
But in this case you could instead use DateFormat.parse(String, ParsePosition).
You can take advantage of regular expressions to determine which format the string is in, and whether it matches any valid format. Something like this (not tested):
(Oops, I wrote this in C# before checking to see what language you were using.)
Regex test = new Regex(#"^(?:(?<formatA>\d{2}-[a-zA-Z]{3}-\d{2})|(?<formatB>\d{2}/\d{2}/\d{3}))$", RegexOption.Compiled);
Match match = test.Match(yourString);
if (match.Success)
{
if (!string.IsNullOrEmpty(match.Groups["formatA"]))
{
// Use format A.
}
else if (!string.IsNullOrEmpty(match.Groups["formatB"]))
{
// Use format B.
}
...
}
If you formats are exact (June 7th 1999 would be either 07-Jun-99 or 07/06/1999: you are sure that you have leading zeros), then you could just check for the length of the string before trying to parse.
Be careful with the short month name in the first version, because Jun may not be June in another language.
But if your data is coming from one database, then I would just convert all dates to the common format (it is one-off, but then you control the data and its format).
In this limited situation, the best (and fastest method) is certinally to parse out the day, then based on the next char either '/' or '-' try to parse out the rest. and if at any point there is unexpected data, return NULL then.
Assuming the patterns you gave are the only likely choices, I would look at the String passed in to see which format to apply.
public Date parseDate(final String date) {
if (date == null) {
return null;
}
SimpleDateFormat format = (date.charAt(2) == '/') ? new SimpleDateFormat("dd/MMM/yyyy")
: new SimpleDateFormat("dd-MMM-yy");
try {
return format.parse(date);
} catch (ParseException e) {
// Log a complaint and include date in the complaint
}
return null;
}
As others have mentioned, if you can guarantee that you will never access the DateFormats in a multi-threaded manner, you can make class-level or static instances.
Looks like three options if you only have two, known formats:
check for the presence of - or / first and start with that parsing for that format.
check the length since "dd-MMM-yy" and "dd/MM/yyyy" are different
use precompiled regular expressions
The latter seems unnecessary.
Use regular expressions to parse your string. Make sure that you keep both regex's pre-compiled (not create new on every method call, but store them as constants), and compare if it actually is faster then the try-catch you use.
I still find it strange that your method returns null if both versions fail rather then throwing an exception.
you could use split to determine which format to use
String[] parts = date.split("-");
df = (parts.length==3 ? format1 : format2);
That assumes they are all in one or the other format, you could improve the checking if need be
An alternative to creating a SimpleDateFormat (or two) per iteration would be to lazily populate a ThreadLocal container for these formats. This will solve both Thread safety concerns and concerns around object creation performance.
A simple utility class I have written for my project. Hope this helps someone.
Usage examples:
DateUtils.multiParse("1-12-12");
DateUtils.multiParse("2-24-2012");
DateUtils.multiParse("3/5/2012");
DateUtils.multiParse("2/16/12");
public class DateUtils {
private static List<SimpleDateFormat> dateFormats = new ArrayList<SimpleDateFormat>();
private Utils() {
dateFormats.add(new SimpleDateFormat("MM/dd/yy")); // must precede yyyy
dateFormats.add(new SimpleDateFormat("MM/dd/yyyy"));
dateFormats.add(new SimpleDateFormat("MM-dd-yy"));
dateFormats.add(new SimpleDateFormat("MM-dd-yyyy"));
}
private static Date tryToParse(String input, SimpleDateFormat format) {
Date date = null;
try {
date = format.parse(input);
} catch (ParseException e) {
}
return date;
}
public static Date multiParse(String input) {
Date date = null;
for (SimpleDateFormat format : dateFormats) {
date = tryToParse(input, format);
if (date != null) break;
}
return date;
}
}
On one hand I see nothing wrong with your use of try/catch for the purpose, it’s the option I would use. On the other hand there are alternatives:
Take a taste from the string before deciding how to parse it.
Use optional parts of the format pattern string.
For my demonstrations I am using java.time, the modern Java date and time API, because the Date class used in the question was always poorly designed and is now long outdated. For a date without time of day we need a java.time.LocalDate.
try-catch
Using try-catch with java.time looks like this:
DateTimeFormatter ddmmmuuFormatter = DateTimeFormatter.ofPattern("dd-MMM-uu", Locale.ENGLISH);
DateTimeFormatter ddmmuuuuFormatter = DateTimeFormatter.ofPattern("dd/MM/uuuu");
String dateString = "07-Jun-09";
LocalDate result;
try {
result = LocalDate.parse(dateString, ddmmmuuFormatter);
} catch (DateTimeParseException dtpe) {
result = LocalDate.parse(dateString, ddmmuuuuFormatter);
}
System.out.println("Date: " + result);
Output is:
Date: 2009-06-07
Suppose instead we defined the string as:
String dateString = "07/06/2009";
Then output is still the same.
Take a taste
If you prefer to avoid the try-catch construct, it’s easy to make a simple check to decide which of the formats your string conforms to. For example:
if (dateString.contains("-")) {
result = LocalDate.parse(dateString, ddmmmuuFormatter);
} else {
result = LocalDate.parse(dateString, ddmmuuuuFormatter);
}
The result is the same as before.
Use optional parts in the format pattern string
This is the option I like the least, but it’s short and presented for some measure of completeness.
DateTimeFormatter dateFormatter
= DateTimeFormatter.ofPattern("[dd-MMM-uu][dd/MM/uuuu]", Locale.ENGLISH);
LocalDate result = LocalDate.parse(dateString, dateFormatter);
The square brackets denote optional parts of the format. So Java first tries to parse using dd-MMM-uu. No matter if successful or not it then tries to parse the remainder of the string using dd/MM/uuuu. Given your two formats one of the attempts will succeed, and you have parsed the date. The result is still the same as above.
Link
Oracle tutorial: Date Time explaining how to use java.time.