使用正则表达式提取和重新格式化时间戳的唯一方法？

Question

I need to read a list of timestamps and sort them by "oldest" and "newest" order. But before I can sort them, I need to reformat them first. Those timestamps are in the following format:

mm:hh PM/AM dd Month(egJun) yyyy ,

For example:

• 3:40 PM 1 Jun 2016
• 11:40 AM 11 Jun 2016

I am using Regex to extract and reformat each timestamp into a format that Java will recognize, eg dd Month(eg Jun) yyyy hh:mm

What I have done is as following:

package regularExpressionDate;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class regularExpressionDate {

    public static void main(String[] args) {
        String pattern = "^(\\d{1,2}):(\\d{1,2})\\s(PM|AM)\\s(\\d{1,2})\\s(\\w{3})\\s(\\d{4})$";
        String date1 = "3:40 PM 1 Jun 2016";
        String newDate1;
        int hour;

        Pattern r = Pattern.compile(pattern);
        Matcher m1 = r.matcher(date1);

        if(m1.find()) {
            hour = Integer.parseInt(m1.group(1));
            if(m1.group(3).equals("PM")) {
                hour+=12;
                System.out.println(m1.group(3));
            }
            newDate1 = (m1.group(4) + " " + m1.group(5) + " " + m1.group(6) + " " + hour + ":" + m1.group(2));
            System.out.println(newDate1);
        }
        else {
            System.out.println("No match");
        }
    }
}

For input 3:40 PM 1 Jun 2016 , I got 1 Jun 2016 15:40 .

My question is:

• Is my approach the best way to achieve my goal in terms of clarity and efficiency? I was hoping there would a method that could convert into Java recognized timestamp format right away, but I did not find it.

Answer 1

You can use the Stream API to parse and sort multiple dates

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("h:mm a d MMM yyyy");
List<LocalDateTime> dates =
        Stream.of("3:40 PM 1 Jun 2016", "11:40 AM 11 Jun 2016")
                .map(text -> LocalDateTime.parse(text, formatter))
                .sorted()
                .collect(Collectors.toList());
System.out.println(dates);

prints

[2016-06-01T15:40, 2016-06-11T11:40]

Answer 2

I went this way using parser.

    LocalDateTime ldt = LocalDateTime.parse("11:40 AM 11 Jun 2016", DateTimeFormatter.ofPattern("h:m a d MMM yyyy"));
    System.out.println(ldt);

If you have multiple white spaces, you can clear input before parsing

 String inputDate = "11:40    AM    11   Jun 2016";
 inputDate = inputDate.replaceAll("[ ]+", " ");

For multiple dates, move formatter.

 //BTW, it is thread-safe.
 private static final DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("h:m a d MMM yyyy");


 //---
 LocalDateTime ldt = LocalDateTime.parse(input, FORMATTER);

Answer 3

You can parse your date String to Java Date by using SimpleDateFormat

    String date = "3:40 PM 1 Jun 2016";

    SimpleDateFormat formatter = new SimpleDateFormat("hh:mm a dd MMM yyyy");
    Date startDate = formatter.parse(date);
    System.out.println(startDate);

After this you can sort date objects using comparator.

Answer 4

You can do something like this :

Convert string dates to Date and then add them to a list (collection) and sort them.

Check out the working example here !!

    // Your dates to sort
    String dates[] = {"3:40 PM 1 Jun 2016", "11:40 AM 11 Jun 2016"}; 

    List<Date> lst = new ArrayList<>();
    // Your date format
    DateFormat format = new SimpleDateFormat("hh:mm a dd MMM yyyy"); 

    for(String str : dates){
        //creating the collection of your dates converted to java dates
        lst.add(format.parse(str)); 
    }

    //sorting  the dates
    Collections.sort(lst);

    //converting the dates into new format (if required)
    DateFormat newFormat = new SimpleDateFormat("dd MMM yyyy HH:mm");
    for(Date date : lst){
        System.out.println(newFormat.format(date));
    }