title: JAXB duplicate object
body: <p>How to avoid creating different object instances when they are suppose to be the same ?</p>
  
  <p>Here is the xml file :</p>
  
  <pre><code>&lt;family&gt;
      &lt;person&gt;
          &lt;firstName&gt;John&lt;/firstName&gt;
          &lt;father&gt;
              &lt;firstName&gt;Gary&lt;/firstName&gt;
          &lt;/father&gt;
          &lt;mother&gt;
              &lt;firstName&gt;Jane&lt;/firstName&gt;
          &lt;/mother&gt;
      &lt;/person&gt;
      &lt;person&gt;
          &lt;firstName&gt;Philip&lt;/firstName&gt;
          &lt;father&gt;
              &lt;firstName&gt;Franck&lt;/firstName&gt;
          &lt;/father&gt;
          &lt;mother&gt;
              &lt;firstName&gt;Jane&lt;/firstName&gt;
          &lt;/mother&gt;
      &lt;/person&gt;
  &lt;/family&gt;
  </code></pre>
  
  <p>father and mother elements are of type <code>Person</code>.
  I have two persons with the same mother, when I unmarsharll the xml file it creates two different instances of Person class.  Is there a way to tell that they should be the same object ?</p>