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

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

public class XxxTag extends RequestContextAwareTag {
  //覆盖doStartTagInternal方法
  protected int doStartTagInternal() throws Exception {
      this.getRequestContext().getWebApplicationContext().getBean("beanName");
      
  }
}

------解决方案--------------------

在标签中可以通过pageContext得到servletContext
Java code
ApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(pageContext.getServletContext());
XxxService service = (XxxService)ctx.getBean("beanName");