struts2 action中替多个对象赋值方法

struts2 action中为多个对象赋值方法
例子:
<form method="post" action="Test_Action">
  <input type="text" name="user.username" />
<input type="text" name="admin.name"/>
<input type="submit" value="submit" />
</form>

在action中:
public class Test_Action {
  private User user;
  private Admin admin;

  // get() set()
  public String execute(){
    system.out.println("user = "+ user.getUsername() + " admin = "+ admin.getName());
}
}