Java 在ehcache xml中配置堆大小

我的ehcache.xml中有以下条目

<config
        xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
        xmlns:jsr107='http://www.ehcache.org/v3/jsr107'
        xmlns='http://www.ehcache.org/v3'
        xsi:schemaLocation="
        http://www.ehcache.org/v3 http://www.ehcache.org/schema/ehcache-core-3.2.xsd
        http://www.ehcache.org/v3/jsr107 http://www.ehcache.org/schema/ehcache-107-ext-3.2.xsd">
    <service>
        <jsr107:defaults enable-management="true" enable-statistics="true"/>
    </service>

    <cache alias="testsCache" uses-template="testsCache">
        <expiry>
            <none/>
        </expiry>
    </cache>

    <cache-template name="testsCache">
        <key-type>java.lang.String</key-type>
        <value-type>com.test.Test</value-type>
        <listeners>
            <listener>
                <!-- the the main cache event listener-->
                <class>com.test.CacheEventLogger</class>
                <event-firing-mode>ASYNCHRONOUS</event-firing-mode>
                <event-ordering-mode>UNORDERED</event-ordering-mode>
                <events-to-fire-on>CREATED</events-to-fire-on>
                <events-to-fire-on>UPDATED</events-to-fire-on>
                <events-to-fire-on>EXPIRED</events-to-fire-on>
                <events-to-fire-on>REMOVED</events-to-fire-on>
                <events-to-fire-on>EVICTED</events-to-fire-on>
            </listener>
        </listeners>
        <resources>
            <heap unit="MB">"${heap.size}"</heap>
        </resources>
    </cache-template>
</config>

application.yml

heap.size:100

如何配置

Caused by: org.xml.sax.SAXParseException: cvc-datatype-valid.1.2.1: '"${heap.size}"' is not a valid value for 'integer'