RegEx to replace to given date with the current date

Question

I have deserialized json to string variable where i wanted to update below variable to current date in all occurrence

"buyDate":"2019-04-09T13:21:00.866Z",

String result = content.replaceAll("(\"buyDate\":\"(\\d{4}-\\d{2}-\\d{2}\\.*$)\")", "\"buyDate\":" + LocalDate.now().toString() + "\"");

but above logic is failing. Can someone please suggest solution.

I think `String.replaceAll` is not the best idea when it comes to manipulating JSON data... Think about deserializing the JSON to objects, manipulating their values and re-writing the JSON file. — deHaar, Jun 16 '20 at 09:21

score 1 · Accepted Answer · 2020-06-16T10:46:02.193

I would recommend using parsers for parsing and amending dynamic JSON data. However, if the JSON is static and you want to achieve your result using regex; then your regex is very correct(although it can be compacted. See in answer). You just need to use LocalDateTime instance instead of LocalDate instance. Something like;

// Sample code. Please manipulate according to your requirements.
import java.time.*;

public class Main
{
    public static void main(String[] args) {
        // Sample test String
        String content = "\"buyDate\":\"2019-04-09T13:21:00.866Z\"";
       // String result = content.replaceAll("(\"buyDate\":\"(\\d{4}-\\d{2}-\\d{2}.*)\")", "\"buyDate\":\"" 
        //+ LocalDateTime.now().toString() + "Z\"");
// COMPACTED REGEX
        String result = content.replaceAll("(\"buyDate\":\".*?\"", "\"buyDate\":\"" 
        + LocalDateTime.now().toString() + "Z\"");
        System.out.println(result);
    }
}
// Outputs: "buyDate":"2020-06-16T09:33:38.276Z" a.t. online IDE's local time.

You can find the sample run of the above code in here.

If you want to replace only date value leaving time and zero-hour format as it is(although I don't see any practical reason to do so); then you could try this:

import java.time.*;
import java.time.format.*;
import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Main
{
    public static void main(String[] args) {
        LocalDate dt = LocalDate.now();
        final String regex = "\"buyDate\":\"(\\d{4}-\\d{2}-\\d{2})T";
        final String string = "\"buyDate\":\"2019-04-09T13:21:00.866Z\"";
        DateTimeFormatter formatDateToday=DateTimeFormatter.ofPattern("YYYY-MM-dd");
        final String subst = "\"buyDate\":\""+ dt.format(formatDateToday) +"T";

        final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
        final Matcher matcher = pattern.matcher(string);

        // The substituted value will be contained in the result variable
        final String result = matcher.replaceAll(subst);
        System.out.println(result);
    }
}

I used DateTimeFormatter class for formatting the Date.
I used Pattern and Matcher class to match only the dates in the given JSON string.

You can find the sample run of the above code in here.

score 0 · Answer 2 · edited Jun 17 '20 at 08:50

Why is there a $ and then its followed by \" in the regex? This will suffice "(\"buyDate\":\"(\\d{4}-\\d{2}-\\d{2}.*)\")".

Your final code will be like

String result = content.replaceAll("(\"buyDate\":\"(\\d{4}-\\d{2}-\\d{2}.*)\")", "\"buyDate\":" + LocalDate.now().toString() + "\"");

You should use java.time package classes for cleaner manipulation.

RegEx to replace to given date with the current date

2 Answers2