spring 读取properties的两种方法

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="locations" value="classpath:com/foo/jdbc.properties"/>
</bean>

<property name="url" value="${jdbc.url}"/>

<beans xmlns="http://www.springframework.org/schema/beans" 
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" 
     xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" 
     xsi:schemaLocation="http://www.springframework.org/schema/beans 
            http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
            http://www.springframework.org/schema/context 
            http://www.springframework.org/schema/context/spring-context-3.0.xsd 
            http://www.springframework.org/schema/aop 
            http://www.springframework.org/schema/aop/spring-aop-3.0.xsd 
            http://www.springframework.org/schema/tx 
            http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">

xmlns:context=http://www.springframework.org/schema/context

<context:property-placeholder location="dbconf.properties"/>