struts2的java文件中不能直接弹出script对话框

ServletResponseAware

public class Login extends ActionSupport implements SessionAware,ServletResponseAware
{

private HttpServletResponse response = null;
　　　　....
public void setServletResponse(HttpServletResponse response) {
// TODO Auto-generated method stub
this.response = response;
}

public String execute()
{
Person person = new Person();
PersonDAO personDAO = new PersonDAO();
if(personDAO.findById(id)==null)
{
System.out.println("用户不存在");
try {
response.setContentType("text/html; charset=UTF-8");
response.setCharacterEncoding("UTF-8");        //防止乱码；
PrintWriter out = response.getWriter();
out.print("<Script>alert('用户不存在!')</Script>");
out.flush();
out.close();
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
....
}
}