Question

I’m trying to extract hours, minutes, seconds, and nanoseconds from a string time stamp in a log file.Here is the input string I am testing with:

 SOME_TEXT,+09:30:01.040910105,SOME_TEXT,SOME_TEXT,SOME_TEXT

In Perl/Python, I would use the following regex to group the fields I am interested in:

 (\d\d)\:(\d\d)\:(\d\d)\.(\d{9})

You can verify that the regex works with the test string at http://regexpal.com if you’re curious.

So I tried to write a simple Java program that can extract the fields:

import java.util.regex.*;

public class Driver
{
  static public void main(String[] args)
  {
    String t = new String("SOME_TEXT,+09:30:01.040910105,SOME_TEXT,SOME_TEXT,SOME_TEXT");
    Pattern regex = Pattern.compile("(\\d\\d):(\\d\\d):(\\d\\d)\\.(\\d{9})");
    Matcher matches = regex.matcher(t);
    for (int i=1; i<matches.groupCount(); ++i)
    {
      System.out.println(matches.group(i));
    }
  }
}

My regex did not translate correctly, however. The following exception shows that it did not find any matches:

 Exception in thread "main" java.lang.IllegalStateException: No match found
   at java.util.regex.Matcher.group(Matcher.java:485)
   at Driver.main(Driver.java:12)

How would I properly translate the regex from Perl/Python style to Java?

Answer 1

The regex itself is fine. There are, however, two problems with the code:

1. you need to call Matcher.find();
2. you need to fix the for loop (it should use <= instead of <).

Here is the corrected version:

public class Driver
{
  static public void main(String[] args)
  {
    String t = new String("SOME_TEXT,+09:30:01.040910105,SOME_TEXT,SOME_TEXT,SOME_TEXT");
    Pattern regex = Pattern.compile("(\\d\\d):(\\d\\d):(\\d\\d)\\.(\\d{9})");
    Matcher matcher = regex.matcher(t);
    while (matcher.find()) {
        for (int i=1; i<=matcher.groupCount(); ++i)
        {
          System.out.println(matcher.group(i));
        }
    }
  }
}

This prints out:

09
30
01
040910105