follow up re: key execution speed

I wrote in last week and received much good advice on using keys to perform
lookups during XSL execution.  I was advised, properly I am sure, that keys
are damn fast and the best way to do nearly anything.  However my problem is
a little unusual, and is resulting in unsatisfactory performance.

The trick is this: while I have been advised that keys are speed for any
lookup that will be performed more than once in a transform, my situation is
a little more complicated. I only do this lookup once per transform, but I
perform this transform many times (thousands!) on different source
documents.  I was hoping to get the speed benefit of the key across these
multiple transformations.

My XSL templates make use of two data files, Zips.xml, which maps zip codes
to dealer codes, and Dealers.xml, which contains information about each
dealer. The idea is to use a key (ziptorc) over the (very large - 400K) Zips
file (looks like <ZIP zip='10001' rc='2'/>) to perform the zip-to-dealer
mapping, then to use another key over the dealer file (rctodealer) to
perform a generic templating of the dealer informaiton. My templates are as
follows:

<xsl:key name="ziptorc" match="ZIP" use="@zip"/>
<xsl:key name="rctodealer" match="DEALER" use="@rc"/>
<xsl:template name="TARGETBYZIP">
	<!-- target by ZIP -->
	<xsl:variable name="ZIP">
		<xsl:value-of select="ZIP/@val"/>
	</xsl:variable>
	<xsl:variable name="RC">
		<xsl:for-each select="document('Zips.xml')">
			<xsl:value-of select="key('ziptorc', $ZIP)/@rc"/>
		</xsl:for-each>
	</xsl:variable>
	<xsl:for-each select="document('Dealers.xml')">
		<xsl:apply-templates select="key('rctodealer', $RC)"/>
	</xsl:for-each>
</xsl:template>

<xsl:template match="DEALER">
	<!-- generic template for displaying dealer information here -->
</xsl:template>

I am using Xalan, creating and persisting a Templates object. I am then
creating a Transformer object to perform each transform. Performance is very
slow; seems to me that it is reloading the data files and recreating the
keys every time it performs the transform.

Is there some set of changes, to the XSL or to the Java, that will enable me
to get the blazing performance I require?

Thanks very much for your help.

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