RegEx in Java: Problem with newline

Question

I am currently trying to learn how to use regular expressions so pelase bear with my simple question. For example, say I have an input file containing a bunch of links separated by a newline:

www.foo.com/Archives/monkeys.htm
Description of Monkey's website.

www.foo.com/Archives/pigs.txt
Description of Pig's website.

www.foo.com/Archives/kitty.txt
Description of Kitty's website.

www.foo.com/Archives/apple.htm
Description of Apple's website.

If I wanted to get one website along with its description, this regex seems to work on a testing tool: .*www.*\\s.*Pig.*

However, when I try running it within my code it doesn't seem to work. Is this expression correct? I tried replacing "\s" with "\n" and it doesn't seem to work still.

Answer 1

Works for me:

import java.util.regex.Pattern;
import java.util.regex.Matcher;
public class Foo {
  public static void main(String args[]) {
    Pattern p = Pattern.compile(".*www.*\\s.*Pig.*");
    String s = "www.foo.com/Archives/monkeys.htm\n"
             + "Description of Monkey's website.\n"
             + "\n"
             + "www.foo.com/Archives/pigs.txt\n"
             + "Description of Pig's website.\n"
             + "\n"
             + "www.foo.com/Archives/kitty.txt\n"
             + "Description of Kitty's website.\n"
             + "\n"
             + "www.foo.com/Archives/apple.htm\n"
             + "Description of Apple's website.\n";
    Matcher m = p.matcher(s);
    if (m.find()) {
      System.out.println(m.group());
    } else {
      System.out.println("ERR: no match");
    }
  }
}

Perhaps the problem was with the way you were using the Pattern and Matcher objects?

Answer 2

The lines are probably separated by \r\n in your file. Both \r (carriage return) and \n (linefeed) are considered line-separator characters in Java regexes, and the . metacharacter won't match either of them. The \s in your regex will match the \r but not the \n, so the match fails. Your tester probably used just \n to separate the lines.

If I'm right, changing the \s to \s+ or [\r\n]+ should get it to work. That's probably all you need to do in this case, but sometimes you have to match exactly one line separator, or at least keep track of how many you're matching. In that case you need a regex that matches exactly one of any of the three most common line separator types: \r\n (Windows/DOS), \n (Unix/Linus/OSX) and \r (older Macs). Either of these will do:

"\r\n|[\r\n]"

"\r?\n|\r\n"

Answer 3

try this

([^\r]+\r[^\r])+

Answer 4

This version matches newlines that may be either Windows (\r\n) or Unix (\n)

Pattern p = Pattern.compile("(www.*)((\r\n)|(\n))(.*Pig.*)");
String s = "www.foo.com/Archives/monkeys.htm\n"
           + "Description of Monkey's website.\n"
           + "\r\n"
           + "www.foo.com/Archives/pigs.txt\r\n"
           + "Description of Pig's website.\n"
           + "\n"
           + "www.foo.com/Archives/kitty.txt\n"
           + "Description of Kitty's website.\n"
           + "\n"
           + "www.foo.com/Archives/apple.htm\n"
           + "Description of Apple's website.\n";
Matcher m = p.matcher(s);
if (m.find()) {
  System.out.println("found: "+m.group());
  System.out.println("website: "+m.group(1));
  System.out.println("description: "+m.group(5));
}
System.out.println("done");