title: webflow evaluate expression doesn't call method
body: <p>in the flow:</p>
  
  <pre><code>&lt;action-state id="create"&gt;
          &lt;evaluate expression="operatore_rer" result="flowScope.operatore_rer" /&gt;
          &lt;evaluate expression="mainService.getComuni()" result="flowScope.comuni_list" /&gt;
          &lt;transition to="nuovo-operatore-rer" /&gt;
      &lt;/action-state&gt;
  </code></pre>
  
  <p>evaluate expression doesn't call the method mainService.getComuni()</p>
  
  <p>where and how i have to declare mainService????</p>
  
  <p>if i declare this in applicationContext:</p>
  
  <pre><code>&lt;bean id="mainService" class="com.aieap.services.MainService" /&gt;
  </code></pre>
  
  <p>this is the error:</p>
  
  <pre><code>GRAVE: StandardWrapper.Throwable
  org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mainService' defined in ServletContext resource [/WEB-INF/dispatch-servlet.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.aieap.services.MainService]: Specified class is an interface
  </code></pre>
  
  <p>help me </p>