title: The best way to add a time span (long and TimeUnit) to a java.util.Date?
body: <p>I'm trying to implement this method:</p>
  
  <pre><code>/**
   * Adds the given span to the given date and returns a new date.
   */
  public java.util.Date add(java.util.Date d, long span, java.util.concurrent.TimeUnit unit) {
      // ...
  }
  </code></pre>
  
  <p>I can just do a switch on the unit. Is there a library that does this? apache commons? Joda?</p>