ibatis 中isNull, isNotNull与isEmpty, isNotEmpty区别

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<span style="font-family: Arial, Verdana, sans-serif; white-space: normal; "><strong>isNull, isNotNull与isEmpty, isNotEmpty区别</strong></span> 
在iBATIS中isNull用于判断参数是否为Null，isNotNull相反
isEmpty判断参数是否为Null或者空，满足其中一个条件则其true
isNotEmpty相反，当参数既不为Null也不为空是其为true
判断之后做相对应的表达式操作

如下代码：
  
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<select id="getCustomerRegNum" resultClass="int" parameterClass="QueryCustomerCondition"> 
          select count(cus_id) from cus_customer_tbl  
          <dynamic prepend="WHERE"> 
            <isNotEmpty prepend="AND" property="cusWebFrom"> 
                ( CUS_CUSTOMER_TBL.CUS_WEB_FROM LIKE '%$cusWebFrom$%') 
            </isNotEmpty> 
            <isNotEmpty prepend="AND" property="cusWebAgent"> 
                ( CUS_CUSTOMER_TBL.CUS_WEB_AGENT LIKE '%$cusWebAgent$%') 
            </isNotEmpty> 
          </dynamic> 
   </select> 

当之传入参数 cusWebForm 而不传入 cusWebAgent 时，产生的SQL语句为：
select count(cus_id) from cus_customer_tbl    WHERE      ( CUS_CUSTOMER_TBL.CUS_WEB_FROM LIKE '%baidu%')

而当XML代码用<isNotNull > 配置时（注意他们的区别），
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<select id="getCustomerRegNum" resultClass="int" parameterClass="QueryCustomerCondition"> 
          select count(cus_id) from cus_customer_tbl  
          <dynamic prepend="WHERE"> 
            <isNotNull prepend="AND" property="cusWebFrom"> 
                ( CUS_CUSTOMER_TBL.CUS_WEB_FROM LIKE '%$cusWebFrom$%') 
            </isNotNull> 
            <isNotNull prepend="AND" property="cusWebAgent"> 
                ( CUS_CUSTOMER_TBL.CUS_WEB_AGENT LIKE '%$cusWebAgent$%') 
            </isNotNull> 
          </dynamic> 
   </select> 

同样 ，当之传入参数 cusWebForm 而不传入 cusWebAgent 时，产生的SQL语句为：
select count(cus_id) from cus_customer_tbl     WHERE     ( CUS_CUSTOMER_TBL.CUS_WEB_FROM LIKE '%baidu%')      AND        (CUS_CUSTOMER_TBL.CUS_WEB_AGENT LIKE '%%')

从Sql 语句就能看出他们的区别。。。。。