title: retain the existing selection and allow user to add more selection in struts2 select tag
body: <p>How can I retain the existing selection from the list when the user makes further selection in struts tag <code>select</code>. </p>
  
  <p><strong>JSP:</strong></p>
  
  <pre><code>&lt;s:select key="chosenId" id="chosenId" name="entity.IdList" listKey="iD" list="idList" listValue="idName" size="5" multiple="true"/&gt;
  </code></pre>
  
  <p>For example: existing selection is <code>"Finance"</code> and test for certain object ( refer to image). When user edit that the particular object, he might want to select another <code>id</code> name. </p>
  
  <p><strong>The problem is when user tries to select in the select box, the current selection disappears. So I want to retain the existing selection and allow the user to select more.</strong></p>
  
  <p>What kind of approach should I make to get this kind of feature?</p>
  
  <p><img src="https://i.stack.imgur.com/5JHsv.png" alt="enter image description here"></p>