Extract multiple dates (dd-MMM-yyyy format) from a string in java

Question

I have searched everywhere for this but couldn't get a specific solution, and the documentation also didn't cover this. So I want to extract the start date and end date from this string "1-Mar-2019 to 31-Mar-2019". The problem is I'm not able to extract both the date strings.

I found the closest solution here but couldn't post a comment asking how to extract values individually due to low reputation: https://stackoverflow.com/a/8116229/10735227

I'm using a regex pattern to look for the occurrences and to extract both occurrences to 2 strings first.
Here's what I tried:

Pattern p = Pattern.compile("(\\d{1,2}-[a-zA-Z]{3}-\\d{4})");  
Matcher m = p.matcher(str);
while(m.find())
{
    startdt = m.group(1); 
    enddt = m.group(1);   //I think this is wrong, don't know how to fix it
}
System.out.println("startdt: "+startdt+" enddt: "+enddt);

Output is:

startdt: 31-Mar-2019 enddt: 31-Mar-2019

Additionally I need to use DateFormatter to convert the string to date (adding the trailing 0 before single digit date if required).

Actually, you extract the two dates with your code. It takes two iterations in the while block. Do you mean to get both with 1 regex "at once"? — Wiktor Stribiżew, Jul 02 '19 at 08:33
maybe you can do something like this Pattern p = Pattern.compile("(\\d{1,2}-[a-zA-Z]{3}-\\d{4}) to (\\d{1,2}-[a-zA-Z]{3}-\\d{4})"); Matcher m = p.matcher(str); while(m.find()) { startdt = m.group(1); enddt = m.group(2); } — Akash, Jul 02 '19 at 08:40
@WiktorStribiżew I mean to get the 2 dates into the 2 strings whether at once or through a loop if required — Arun Koundinya, Jul 02 '19 at 08:40
Sorry, I forgot to mention that the string will have 2 dates but could have from at the beginning some times. Should I edit the question? — Arun Koundinya, Jul 02 '19 at 08:47
@ArunKoundinya FYI: with [this solution](https://stackoverflow.com/a/56848621/3832970), you are not checking a range. You will get `2-Feb-2019` and `1-Mar-2019` in `2-Feb-2019: 1-Mar-2019 to 31-Mar-2019`, not the expected `1-Mar-2019` and `31-Mar-2019`. It is OK as per your question title though. Just your data implies that you need to match ranges. — Wiktor Stribiżew, Jul 03 '19 at 08:23
@WiktorStribiżew thanks for the info but the string will have just the 2 dates, so I see no problem with it, I can use your solution in case that situation does come up — Arun Koundinya, Jul 03 '19 at 09:50

score 1 · Accepted Answer · answered Jul 02 '19 at 08:47

1

You can catch both dates simply calling the find method twice, if you only have one, this would only capture the first one :

String str = "1-Mar-2019 to 31-Mar-2019";

String startdt = null, enddt = null;

Pattern p = Pattern.compile("(\\d{1,2}-[a-zA-Z]{3}-\\d{4})");  
Matcher m = p.matcher(str);
if(m.find()) {
    startdt = m.group(1); 
    if(m.find()) {
       enddt = m.group(1);
    }
}   
System.out.println("startdt: "+startdt+" enddt: "+enddt);

Note that this could be used with a while(m.find()) and a List<String to be able to extract every date your could find.

answered Jul 02 '19 at 08:47

AxelH

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Best suggestion this far, imho. You might also use a longer regex including two dates and capture tham as group 1 and group 2. – Ole V.V. Jul 02 '19 at 08:49
@OleV.V. it was the second part of my answer but [Wiktor Stribiżew's answer](https://stackoverflow.com/a/56848631/4391450) post it first ;) – AxelH Jul 02 '19 at 08:50

Wiktor Stribiżew · Answer 2 · 2019-07-02T08:49:04.340

1

If your text may be messy, and you really need to use a regex to extract the date range, you may use

String str = "Text here 1-Mar-2019 to 31-Mar-2019 and tex there";
String startdt = "";
String enddt = "";

String date_rx = "\\d{1,2}-[a-zA-Z]{3}-\\d{4}";
Pattern p = Pattern.compile("(" + date_rx + ")\\s*to\\s*(" + date_rx + ")");  
Matcher m = p.matcher(str);
if(m.find())
{
    startdt = m.group(1); 
    enddt = m.group(2); 
}
System.out.println("startdt: "+startdt+" enddt: "+enddt);
// => startdt: 1-Mar-2019 enddt: 31-Mar-2019

See the Java demo

Also, consider this enhancement: match the date as whole word to avoid partial matches in longer strings:

Pattern.compile("\\b(" + date_rx + ")\\s*to\\s*(" + date_rx + ")\\b")

If the range can be expressed with - or to you may replace to with (?:to|-), or even (?:to|\\p{Pd}) where \p{Pd} matches any hyphen/dash.

edited Jul 02 '19 at 08:49

answered Jul 02 '19 at 08:47

Wiktor Stribiżew

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I went for `Pattern.compile(regexDate + ".*?" + regexDate);` but didn't had the time to post it! This would be the cleanest way to get both date in one regex – AxelH Jul 02 '19 at 08:48
@AxelH I am not sure `.*?` is best to detect a datetime range, it is usually expressed with `to` or dashes, so I suggest `date_rx + \s*(?:to|\p{Pd})\s* + date_rx`. – Wiktor Stribiżew Jul 02 '19 at 08:51
Yeah, I used a lazy quantifier simply to keep the example readable. But I like that you didn't include the group in `date_rx`, it is reusable ! – AxelH Jul 02 '19 at 08:57

score 0 · Answer 3 · answered Jul 02 '19 at 08:35

0

You can simply use String::split

String range = "1-Mar-2019 to 31-Mar-2019";
String dts [] = range.split(" ");
System.out.println(dts[0]);
System.out.println(dts[2]);

answered Jul 02 '19 at 08:35

Scary Wombat

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Thank you, but I still want to know how to extract the occurrences through regex, because the string could possibly change (but still have the dates) – Arun Koundinya Jul 02 '19 at 08:44

Extract multiple dates (dd-MMM-yyyy format) from a string in java

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