SSH问题，接口问题

package com.crm.common.dao;import com.crm.common.util.PageResult;public interface CommonDAO
{
public abstract void listByPage(String s, PageResult pageresult);
}package com.crm.common.Ibiz;import com.crm.common.dao.CommonDAO;public class BaseBiz
{
private CommonDAO commonDAO; //单例模式
public CommonDAO getCommonDAO()
{
return commonDAO;
} public void setCommonDAO(CommonDAO commonDAO) {
this.commonDAO = commonDAO;
}
}
package com.crm.serviceimpl;
import com.crm.common.Ibiz.BaseBiz;
import com.crm.common.dao.CommonDAO;
import com.crm.common.util.PageResult;public class ChanceService extends BaseBiz
{
public ChanceService()
{
} public void search(SalChance condition, PageResult pageResult)
{
String hql = "select o from SalChance o where 1=1 ";
//注意这行
getCommonDAO().listByPage(hql, pageResult);
}

}
package com.crm.web.action;import com.crm.common.web.baseaction.BaseAction;
import com.crm.entity.SalChance;
import com.crm.serviceimpl.ChanceService;
import com.crm.web.form.ChanceForm;public class ChanceAction extends BaseAction
{ private ChanceService chanceService;
private UserService userService; public ActionForward toList(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response)
throws Exception
{
ChanceForm myForm = (ChanceForm)form;
myForm.getItem().setChcStatus("未指派");
                //注意这行调用ChanceService的search方法
chanceService.search(myForm.getItem(), myForm.getPageResult());

return mapping.findForward("list");
} public void setChanceService(ChanceService chanceService) {
this.chanceService = chanceService;
}}
<tx:advice id="txAdvice" transaction-manager="myHibTxManager">
- <tx:attributes>
  <tx:method name="search*" propagation="SUPPORTS" read-only="true" /> 
  </tx:attributes>
</tx:advice>- <aop:config>
  <aop:pointcut id="serviceMethods" expression="execution(* com.crm.serviceimpl.*.*(..))" /> 
  <aop:advisor advice-ref="txAdvice" pointcut-ref="serviceMethods" /> 
  </aop:config>就是想问DAO里面的listByPage(String s, PageResult pageresult);方法，它明明什么实现都没有，为什么调用他就真的查询得数据出来呢？以上是我觉得有联系的相关代码，能帮解释一下吗