import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/* Simple demo of CSV matching using Regular Expressions.
 * Does NOT use the "CSV" class defined in the Java CookBook, but uses
 * a regex pattern simplified from Chapter 7 of <em>Mastering Regular 
 * Expressions</em> (p. 205, first edn.)
 * @version $Id: CSVRE.java,v 1.16 2004/04/25 19:43:32 ian Exp $
 */
public class CSVRE {	
	/** The rather involved pattern used to match CSV's consists of three
	 * alternations: the first matches aquoted field, the second unquoted,
	 * the third a null field.
	 */
	public static final String CSV_PATTERN = "\"([^\"]+?)\",?|([^,]+),?|,";
	private static Pattern csvRE;

	public static void main(String[] argv) throws IOException {
		System.out.println(CSV_PATTERN);
		new CSVRE().process(new BufferedReader(new InputStreamReader(System.in)));
	}
	
	/** Construct a regex-based CSV parser. */
	public CSVRE() {
		csvRE = Pattern.compile(CSV_PATTERN);
	}
	
	/** Process one file. Delegates to parse() a line at a time */
	public void process(BufferedReader in) throws IOException {
		String line;

		// For each line...
		while ((line = in.readLine()) != null) {
			System.out.println("line = `" + line + "'");
			List l = parse(line);
			System.out.println("Found " + l.size() + " items.");
			for (int i = 0; i < l.size(); i++) {
				System.out.print(l.get(i) + ",");
			}
			System.out.println();
		}
	}
	
	/** Parse one line.
	 * @return List of Strings, minus their double quotes
	 */
	public List parse(String line) {
		List list = new ArrayList();
		Matcher m = csvRE.matcher(line);
		// For each field
		while (m.find()) {
			String match = m.group();
			if (match == null)
				break;
			if (match.endsWith(",")) {	// trim trailing ,
				match = match.substring(0, match.length() - 1);
			}
			if (match.startsWith("\"")) { // assume also ends with
				match = match.substring(1, match.length() - 1);
			}
			if (match.length() == 0)
				match = null;
			list.add(match);
		}
		return list;
	}
}