Simple demo of CSV matching using Regular Expressions

[Java Tip]

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;
  }
}