Java 无法解析activemq.base占位符

我尝试将activemq web控制台连接到我的控制台应用程序。下面是应用程序的my context.xml：

<beans xmlns="http://www.springframework.org/schema/beans"
...
 <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <value>activemq.properties</value>
    </property>
 </bean> 

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <value>file:${activemq.base}/conf/credentials.properties</value>
    </property>
</bean>
...

<import resource="${activemq.base}/conf/jetty.xml" />
...

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <list>
            <value>activemq.properties</value>
            <value>file:${activemq.base}/conf/credentials.properties</value>
        </list>
    </property>
</bean>