配置文件导入bean的value值

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:contest="http://www.springframework.org/schema/context"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">


    <!-- 导入配置文件 -->
    <context:property-placeholder location="classpath:db.properties"/>
    <!-- 使用外部属性文件的属性 -->
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="${user}" ></property>
        <property name="password" value="${password}"></property>
        <property name="driverClass" value="${driverclass}"/>
        <property name="jdbcUrl" value="${jdbcurl}"></property>
    </bean>
    <!--<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="root" ></property>
        <property name="password" value="ljwheyxy"></property>
        <property name="driverClass" value="com.mysql.jdbc.Driver"/>
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/mysql"></property>
    </bean>-->

</beans>