Java EE (Java Enterprise Edition) General Discussion

I use JspTag to load data from struts2+spring+hibernate,usually I load data from struts2+spring+hibernate using following code:

public class TestAction extends ActionSupport{
    ......
    WebApplicationContextUtils.getRequiredWebApplicationContext().getBean("testDao");
}

It can run well under struts2+spring+hibernate.

Now I use JspTag using above code,like follows:

public class TestTag extends TagSupport{
   public int doStartTag() throws JspException{
       ......
       WebApplicationContextUtils.getRequiredWebApplicationContext().getBean("testDao");

}

This time when I run my TestTag,it raise following error:
Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException

with this statement---> WebApplicationContextUtils.getRequiredWebApplicationContext().getBean("testDao");

My question is how to load data from struts2+spring+hibernate by using JspTag?

Any idea and source code will be appreciated!

Best regards,
Edward