title: cast object to specific class by string
body: <p>how can i dynamically cast oject to a specific class which is given as a string. e.g.</p>
  
  <pre><code>def a = (ClassA) testService.getObject(xmlString)
  </code></pre>
  
  <p>i would like to do something like this</p>
  
  <pre><code>(grailsApplication.getClassForName(classString)) testService.getObject(xmlString)
  </code></pre>
  
  <p>but the groovy compiler does not like this way of cast operation.</p>