spring使用propertyConfigurer配置连接池出错：报错

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">  
	<property name="locations">  
	    <list>  
	        <value>classpath:config/config.properties</value>  
	    </list>  
	</property>  
</bean>
   
<bean id="dbInfo" class="com.metarnet.noc.db.DbInfo">
	<property name="driver" value="${jdbc.driverClass}" />  
	<property name="url" value="${jdbc.url}" />  
	<property name="user" value="${jdbc.user}" />  
	<property name="password" value="${jdbc.password}" />  
	<property name="initialPoolSize" value="${jdbc.initialPoolSize}" />  
	<property name="minPoolSize" value="${jdbc.minPoolSize}" />  
	<property name="maxPoolSize" value="${jdbc.maxPoolSize}" />
</bean>

<bean id="dataSource" lazy-init="true" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close" >  
	<property name="driverClass" value="com.mysql.jdbc.Driver" />
	<property name="jdbcUrl" value="jdbc:mysql://localhost:3306/spring?useUnicode=true&characterEncoding=UTF-8" />  
	<property name="user" value="root" />  
	<property name="password" value="123456" />  
	<property name="initialPoolSize" value="5" />  
	<property name="minPoolSize" value="2" />  
	<property name="maxPoolSize" value="${jdbc.maxPoolSize}" />  
</bean>

如上面的配置, dbInfo是我用来测试propertyConfigurer赋值的,结果正常, 

可下面的dataSource 死活不能用这种方法配置 , 只要有 ${} 就报错