title: Struts2- extending action classes and thread safety
body: <p>I understand the instance variables on an action class are thread-safe since action classes are instantiated per request. But I have this need for extending action classes and I'm concerned about the thread-safety. </p>
  
  <p>Say, for example I have some common attributes and a few methods handling those attributes among several action classes. I prefer to put them in a single action class and make that extend the <code>ActionSupport</code>. And all action classes will then extend the base action class that I just created. My question is, are the instance variables on the base action class thread-safe? Does S2 manage the base action class at all? </p>
  
  <p>Also what makes an action class an action class to be managed by the S2 and instantiated per request? Getting declared in the <code>struts.xml</code>? Extending <code>ActionSupport</code> class?</p>