How to extract a date from a string and put it into a date variable in Java

Question

I have been looking around stack-overflow and various other websites for the solution to my problem but haven't found any suitable for my specific purposes and have been unable to change these solutions to suit my code. These include regex codes which I do not fully understand or know how to manipulate.

So here is my question, I have a string which has a structure:

"name+" at:"+Date+" Notes:"+meetingnotes"

(name, Date and meetingnotes being variables). What I want to do is extract the date part of the string and stick it in a Date variable. The basic Dateformat for the dates is "yyyy-MM-dd". How do I do this?

Answer 1

For this, a regular expression is your friend:

String input = "John Doe at:2016-01-16 Notes:This is a test";

String regex = " at:(\\d{4}-\\d{2}-\\d{2}) Notes:";
Matcher m = Pattern.compile(regex).matcher(input);
if (m.find()) {
    Date date = new SimpleDateFormat("yyyy-MM-dd").parse(m.group(1));
    // Use date here
} else {
    // Bad input
}

Or in Java 8+:

    LocalDate date = LocalDate.parse(m.group(1));

Answer 2

A date pattern recognition algorithm to not only identify date pattern but also fetches probable date in Java date format. This algorithm is very fast and lightweight. The processing time is linear and all dates are identified in a single pass. Algorithm resolves date using tree traverse mechanism. Tree data structures are custom created to build supported date, time and month patterns.

The algorithm also acknowledges multiple space characters in between Date literals. E.g. DD DD DD and DD DD DD are considered as valid dates.

Following date-patterns are considered as valid and are identifiable using this algorithm.

dd MM(MM) yy(yy) yy(yy) MM(MM) dd MM(MM) dd yy(yy)

Where M is month literal is alphabet format like Jan or January

Allowed delimiters between dates are '/', '\', ' ', ',', '|', '-', ' '

It also recognizes trailing time pattern in following format hh(24):mm:ss.SSS am / pm hh(24):mm:ss am / pm hh(24):mm:ss am / pm

Resolution time is linear, no pattern matching or brute force is used. This algorithm is based on tree traversal and returns back, the list of date with following three components - date string identified in the text - converted & formatted date string - SimpleDateFormat

Using date string and the format string, users are free to convert the string into objects based on their requirements.

The algorithm library is available at maven central.

<dependency>
    <groupId>net.rationalminds</groupId>
    <artifactId>DateParser</artifactId>
    <version>0.3.0</version>
</dependency>

The sample code to use this is below.

 import java.util.List;  
 import net.rationalminds.LocalDateModel;  
 import net.rationalminds.Parser;  
 public class Test {  
   public static void main(String[] args) throws Exception {  
        Parser parser=new Parser();  
        List<LocalDateModel> dates=parser.parse("Identified date :'2015-January-10 18:00:01.704', converted");  
        System.out.println(dates);  
   }  
 }

Output: [LocalDateModel{originalText=2015-january-10 18:00:01.704, dateTimeString=2015-1-10 18:00:01.704, conDateFormat=yyyy-MM-dd HH:mm:ss.SSS, start=18, end=46}]

Detailed blog at http://coffeefromme.blogspot.com/2015/10/how-to-extract-date-object-from-given.html

The complete source is available on GitHub at https://github.com/vbhavsingh/DateParser