tomcat/postgres problem

I'm trying to load the postgresql driver into tomcat using the server.xml file and web.xml file, but I keep getting the following error:

javax.naming.NamingException: DbcpDataSourceFactory: driverClassName is required

Here's part of my server.xml file:

<Resource name="jdbc/MyDB" scope="Shareable" type="javax.sql.DataSource"/>
<ResourceParams name="jdbc/MyDB">
<parameter>
<name>validationQuery</name>
<value></value>
</parameter>
<parameter>
<name>user</name>
<value>Jason</value>
</parameter>
<parameter>
<name>maxWait</name>
<value>5000</value>
</parameter>
<parameter>
<name>maxActive</name>
<value>4</value>
</parameter>
<parameter>
<name>url</name>
<value>jdbc:postgresql:mydb</value>
</parameter>
<parameter>
<name>password</name>
<value> </value>
</parameter>
<parameter>
<name>driverClassName</name>
<value>org.postgresql.Driver</value>
</parameter>
<parameter>
<name>maxIdle</name>
<value>2</value>
</parameter>
</ResourceParams>

And here's part of my web.xml file

<resource-ref>
<description>
Postgresql driver
</description>
<res-ref-name>
jdbc/MyDB
</res-ref-name>
<res-type>
javax.sql.DataSource
</res-type>
<res-auth>
Container
</res-auth>
</resource-ref>

I know I can load the driver with Class.forName(). That works too. But how do I get the driver loaded via the server.xml and web.xml files? Any suggestions?

- Jake