code: public final static String alphanumeric(final String prefix, final int totalLength)
  	{
  		if (prefix.length() >= totalLength)
  			throw new IllegalArgumentException("Cannot generate id of length " +
  			                                   totalLength +
  			                                   ", prefix " +
  			                                   prefix +
  			                                   " takes up that length!");
  
  		return prefix + alphanumeric(totalLength - prefix.length());
  	}
docs: Generates a random sequence of alphanumeric characters, prefixed by <code>prefix</code> such that the total string is of
  length <code>totalLength</code> using a new pseudorandom number
  generator (<code>new Random()</code>)
  
  @param totalLength
  the length of the string to return (must be > the prefix length)
  
  @return a String of length <code>length</code>