Utility Function of the Day

The following example class makes use of JDK 1.4's new Regular Expression classes (In the java.util.regex package) to create a printf(...)-like function.
The comments contain all the information you'll require, so without further ado:

The Code:

import  java.util.*;

import  java.util.regex.*;




/**

 *  Class to show the Regular Expresion example

 */

public class FormatExample

{




  /**

   * Similar to C's printf(...) routine, this method takes an input string with

   * embedded opcodes and replaces these opcodes with the content of specified

   * arguments.

   *

   * The op-code is %{argument_name}, where "argument_name" is the key-name in the

   * specified Properties object that holds the content to fill-in.

   *

   * An example of a string to format would be:

   *  "Welcome %{user_name} and good %{day_part}!"

   *  The Properties object contains two entries:

   *    "user_name" which contains, for example "John Smith" and

   *    "day_part" which contains, for example: "morning".

   *  The resulting string is:

   *     "Welcome John Smith and good morning!"

   *

   *  You could also place any other object as the value for the argument,

   *  as the routine automatically does a "toString()" call to convert the

   *  value of the argument to a string.

   *

   * @param   formatString  The string to format

   * @param   arguments     By-name hash of arguments to fill-in

   * @return  Fully qualified string with all references resolved.

   * @author  Tal Rotbart 

   */

  public  static  String  format(String  formatString,  Properties arguments)

  {

    StringBuffer  formattedString   = new StringBuffer(formatString.length()  * 2);

    Pattern       tokenRegex        = Pattern.compile("%\\{[\\p{Alnum}\\p{Punct}]*\\}");



    if  ((arguments  ==  null) || (arguments.size()  <=  0))

    {

      return  formatString;

    }



    Matcher matcher     = tokenRegex.matcher(formatString);



    /**

     * Match the %{n} instances and replace them with the specified string argument

     */

    while  (matcher.find())

    {

      /**

       * Take the matched argument name and use it

       */

      String  argumentNameString = formatString.substring(matcher.start() + 2, matcher.end() - 1);

      Object  argumentValue      = arguments.get(argumentNameString);



      /**

       * If we do not have the argument, it doesn't mean we have to choke, it may be filled at a later "format" call.

       */

      if  (argumentValue  !=  null)

      {

        /**

         * Recursively resolve the referenced string resources

         */

        matcher.appendReplacement(formattedString, argumentValue.toString());

      }

    }




    /**

     * Append everything after the last match, or from the top if no match

     */

    matcher.appendTail(formattedString);



    return  formattedString.toString();

  }




  /**

   * Main method for testing the "format" routine.

   */

  public static void main(String[] args)

  {

    String      formatString      = "Welcome %{user_name}! Have a good %{day_part}!";

    Properties  formatProperties  = new Properties();



    formatProperties.setProperty("user_name", "John Smith");

    formatProperties.setProperty("day_part", "evening");



    System.out.println("Result  = \"" + format(formatString,  formatProperties) + "\".");

  }




}

Enjoy :)