struts2的拦截器的getInvocationContext()跟使用ActionContext.getContext()有什么不同

struts2的拦截器的getInvocationContext()和使用ActionContext.getContext()有什么不同?
struts2的拦截器的intercept方法中使用invocation.getInvocationContext()和使用ActionContext.getContext()有什么不同?

用

ActionContext.getContext().getsession().put("test","123");

  public String intercept(ActionInvocation invocation)    {ActionContext ac = invocation.getInvocationContext();  String s=(String)ac.getsession.get("test");

 public String intercept(ActionInvocation invocation)  {     ActionContext ac = invocation.getInvocationContext();    ac.getSession().put("test","123");  }

  ActionContext actionContext = ActionContext.getContext();    Map session= actionContext.getSession();   String s2=(String)session.get("test");