I have a huge log file with different types of string rows, and I need to extract data in a "smart" way from these.
Sample snippet:
2011-03-05 node32_three INFO stack trace, at empty string asfa 11120023
--- - MON 23 02 2011 ERROR stack trace NONE
For instance, what is the best way to extract the date from each row, independent of date format?
You could make a regex for different formats like so:
(fmt1)|(fmt2)|....
Where fmt1, fmt2 etc are the individual regexes, for yor example
(20\d\d-[01]\d-[0123]\d)|((?MON|TUE|WED|THU|FRI|SAT|SUN) [0123]\d [01]\d 20\d\d)
Note that to prevent the chance to match arbitrary numbers I restricted year, month and day numbers accordingly. For example, a day number cannot start with 4, neither can a month number start with 2.
This gives the following pseudo code:
// remember that you need to double each backslash when writing the
// pattern in string form
Pattern p = Pattern.compile("..."); // compile once and for all
String s;
for each line
s = current input line;
Matcher m = p.matcher(s);
if (m.find()) {
String d = m.group(); // d is the string that matched
....
}
Each individual date pattern is written in () to make it possible to find out what format we had, like so:
int fmt = 0;
// each (fmt) is a group, numbered starting with 1 from left to right
for (int i = 1; fmt == 0 && i <= total number of different formats; i++)
if (m.group(i) != null) fmt = i;
For this to work, inner (regex) groups must be written (?regex) so that they do not count as capture-groups, look at updated example.