title: Validate struts2 checkbox is checked
body: <p>I would like to validate that a Struts2 checkbox is selected (boolean property) but the validation always fails at the moment. here is what I have:</p>
  
  <pre><code>&lt;s:checkbox key="agreetc" fieldValue="agreedtc"
              label="I have read and agree to the terms and conditions"/&gt;
  
  &lt;field name="agreetc"&gt;
      &lt;field-validator type="fieldexpression"&gt;
          &lt;param name="expression"&gt;agreetc == true&lt;/param&gt;
          &lt;message&gt;You must agree to the terms and conditions&lt;/message&gt;
      &lt;/field-validator&gt;
  &lt;/field&gt;
  </code></pre>
  
  <p>The value of <code>agreetc</code> in the action is always <em>false</em> because the setter for the field never gets called. If I add a String called <code>test</code> with a getter/setter and a <code>s:textfield</code>
  then that value is picked but I can't get the values from <code>s:radio</code>, <code>s:select</code> or <code>s:checkbox</code> in this action. Other actions I have been successful with <code>s:radio</code> and <code>s:select</code>.</p>
  
  <p>Does anyone have any ideas?</p>