Spring读取property文件的两种配置：EL表达式和placeholder表达式

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
  xmlns:context="http://www.springframework.org/schema/context"
  xmlns:util="http://www.springframework.org/schema/util"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">


  <!-- --------------------------properties file---------------------------------- -->
  <!-- resource list -->
  <bean id="resourceList" class="java.util.ArrayList">
    <constructor-arg>
      <list>
        <value>classpath:application-test.properties</value>
        <value>classpath:application-test1.properties</value>
        <value>classpath:application-test2.properties</value>
        <value>classpath:application-test3.properties</value>
      </list>
    </constructor-arg>
  </bean>

  <!-- support expression language -->
  <!-- <util:properties id="testProperties" location="classpath:bootstrap-test.properties" /> -->
  <bean id="configProperties"
    class="org.springframework.beans.factory.config.PropertiesFactoryBean">
    <property name="locations" ref="resourceList">
    </property>
  </bean>

  <!-- support placeholder -->
  <bean id="propertyPlaceholderConfigurer"
    class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="ignoreUnresolvablePlaceholders" value="true" />
    <!-- <property name="locations" ref="resourceList" /> -->
    <property name="properties" ref="configProperties" />
  </bean>

  <!----------------- bean annotation driven -------------------------------- -->
  <context:annotation-config />
  <context:component-scan
    base-package="com.xxx.test" />

  <!-- ------------------import local src/main/resources/ ------------------------- -->
  <import resource="classpath:/config/xxx.beans.xml" />

</beans>