spring.xml从外部文件引入数据库配置信息

<!-- 分散配置 -->
    <context:property-placeholder location="classpath:jdbc.properties" />

    <!-- 数据源 -->
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="driverClass" value="${jdbc.driverclass}" />
        <property name="jdbcUrl" value="${jdbc.url}"></property>
        <property name="user" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />

        <property name="maxPoolSize" value="${c3p0.pool.size.max}" />
        <property name="minPoolSize" value="${c3p0.pool.size.min}" />
        <property name="initialPoolSize" value="${c3p0.pool.size.ini}" />
        <property name="acquireIncrement" value="${c3p0.pool.size.increment}" />
    </bean>

jdbc.properties

jdbc.driverclass=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/springmvcdb?characterEncoding=utf-8
jdbc.username=root
jdbc.password=root

c3p0.pool.size.max=10
c3p0.pool.size.min=2
c3p0.pool.size.ini=3
c3p0.pool.size.increment=2

hibernate.dialect=org.hibernate.dialect.MySQL5Dialect
hibernate.show_sql=true

    <!-- 加载外部的properties文件（方式一），用于解析${}形式的变量。 
        如果需要加载多个properties文件，就写在一起，之间使用逗号隔开。
    <context:property-placeholder location="classpath:cn/yht/spring/k_placeholder/jdbc.properties"/>
    -->

    <!-- 加载外部的properties文件（方式二） 
    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <list>
                <value>classpath:cn/yht/spring/k_placeholder/jdbc.properties</value>
            </list>
        </property>
    </bean>