Tomcat 8 org.apache.catalina.webresources.Cache.getResource

You have few errors:

1. Should be <Resources> (plural)
2. FileResourceSet could be defined in <Resources><PreResource> section if needed and etc... not well documented yet: The Context Container

This works fine for me with Tomcat 8.0.15 & Liferay Portal 6.2.1 GA2 (which has a lot of static files + JDBC pool):

<?xml version='1.0' encoding='utf-8'?>
<Context>
    <WatchedResource>WEB-INF/web.xml</WatchedResource>
    <WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>
    <Resources
        cachingAllowed="true"
        cacheMaxSize="100000"
    />
    <Resource name="jdbc/liferay"
        auth="Container"
        type="javax.sql.DataSource"
        maxActive="64"
        maxIdle="16"
        maxWait="1000"
        username="root"
        password=""
        driverClassName="com.mysql.jdbc.Driver"
        url="jdbc:mysql://localhost/lp_621_ga2_patched?useUnicode=true&amp;characterEncoding=UTF-8&amp;useFastDateParsing=false&amp;autoReconnect=true"
        validationQuery="select 1;"
    />
</Context>