spring配置文件中util:properties和context:property-placeholder用法

<util:properties id="config" location="classpath:db.properties" />
<!-- 配置连接池 -->
<bean id="ds" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<property name="driverClassName" value="#{config.driver}" />
<property name="url" value="#{config.url}" />
<property name="username" value="#{config.username}" />
<property name="password" value="#{config.password}" />
</bean>

xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.2.xsd"

<context:property-placeholder location="classpath:general.properties"/>
<!-- 配置Druid连接池 -->
<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource">
    <!-- 基本属性 driverClassName、url、user、password -->
    <property name="driverClassName" value="${jdbc.driverClassName}"/>
    <property name="url" value="${jdbc.url}" />
    <property name="username" value="${jdbc.username}" />
    <property name="password" value="${jdbc.password}" />
</bean>