Code: regex, formatted output, console

[Christian Kindler]

To get familiar with regex, formatted output and the Console class, I wrote a small program. You can use it learn regex. You can change it / play around with it to solidify your knowledge. And of course you can look for bugs/errors or suggest improvements.

The program asks for a string to search in and a regex pattern. It prints matches with start and end index and it prints the original string with the matches highlighted in bold.

I don't know if printing in bold works in a windows console, it's tested on Linux with bash.

The program comes with no license, so you are totally free to use/change it

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

public class HighlightedConsoleParser {

	public final static char ESC = 27;

	public static void main(String[] args) {
		Console c = System.console();

		String text = c.readLine("%s", "text to parse: ");
		String pattern = c.readLine("%s", "search pattern: ");

		Pattern p = Pattern.compile(pattern);
		Matcher m = p.matcher(text);

		if (printSingleMatches(m)) {
			m.reset();
			printHighlightedResult(m, text);
		} else {
			c.printf("%s", "no matches found.\n");		
		}
	}

	private static boolean printHighlightedResult(Matcher m, String text) {

		Console c = System.console();
		int lastEnd = 0;
		boolean matched = false;

		while (m.find()) {
			int startIdx = m.start();
			int endIdx = m.end();
			
			// print non-matching substrings
			if (startIdx > lastEnd) {
				c.printf("%s", text.substring(lastEnd, startIdx));
			}

			// print matching substrings bold
			startBold(c);
			c.printf("%s", m.group());
			endBold(c);

			lastEnd = endIdx;
			matched = true;
		}
		
		if (matched) {
			// print remaining text after last match			
			if (lastEnd < text.length()) {
				c.printf("%s", text.substring(lastEnd));
			}
			c.printf("%c", '\n');
		}
		return matched;
	}

	private static boolean printSingleMatches(Matcher m) {

		Console c = System.console();
		int i=1;
		boolean matched = false;

		while(m.find()) {
			c.format("hit %1$4d: %2$-6s (start: %3$4d, end: %4$4d)\n", i++, m.group(), m.start(), m.end());
			matched = true;
		}
		return matched;
	}

	private static void startBold(Console c) {
		c.printf("%c[1m", ESC);
	}

	private static void endBold(Console c) {
		c.printf("%c[0m", ESC);
	}
}

[David Marco]

I think that Windows console does not allow for bold fonts. On my machine (Windows Server 2008) the program output shows like:

text to parse: abc1ef6hi7k
search pattern: \d
hit 1: 1 (start: 3, end: 4)
hit 2: 6 (start: 6, end: 7)
hit 3: 7 (start: 9, end: 10)
abc←[1m1←[0mef←[1m6←[0mhi←[1m7←[0mk

Greetings.