java继承问题，求大神帮忙解答

service.impl里面是这么写的
public class ServiceImpl implements Service{
private Dao dao;

public String getDao(){
return dao.getDao();
}
}
下面是dao的代码
public interface Dao {
public String getDao();
}
下面是dao.impl代码
public class DaoImpl implements Dao{
public String getDao(){
//方法
}
}
下面是dao.impl1代码
public class DaoImpl1 implements Dao{
public String getDao(){
//方法
}
}
我怎么能更改一个配置文件改变获取那个dao.impl里面的方法？这个代码应该怎么修改？求大神帮忙~~~~~~

 <!--配置bean,配置后该类由spring管理-->
    <bean name="springAction" class="com.bless.springdemo.action.SpringAction">
        <!--(1)依赖注入,配置当前类中相应的属性-->
        <property name="springDao" ref="springDao"></property>
    </bean>
<bean name="DaoImpl" class="com.bless.springdemo.dao.impl.DaoImpl">
<bean name="DaoImpl1" class="com.bless.springdemo.dao.impl.DaoImpl1">
<bean name="ServiceImpl" class="com.bless.springdemo.dao.impl.ServiceImpl">
  <property name="dao" ref="DaoImpl"></property>  <!--改成DaoImpl1就是另一个了-->
</bean>

如果线程框架的话，那用spring
http://blessht.iteye.com/blog/1162131