Help with parsing configuration using SolrParams/NamedList

[Jay Luker]

Hi,

I'm trying to use a CustomSimilarityFactory and pass in per-field
options from the schema.xml, like so:

 <similarity class="org.ads.solr.CustomSimilarityFactory">
    <lst name="field_a">
        <int name="min">500</int>
        <int name="max">10000</int>
        <float name="steepness">0.5</float>
    </lst>
    <lst name="field_b">
        <int name="min">500</int>
        <int name="max">20000</int>
        <float name="steepness">0.5</float>
    </lst>
 </similarity>

My problem is I am utterly failing to figure out how to parse this
nested option structure within my CustomSimilarityFactory class. I
know that the settings are available as a SolrParams object within the
getSimilarity() method. I'm convinced I need to convert to a NamedList
using params.toNamedList(), but my java fu is too feeble to code the
dang thing. The closest I seem to get is the top level as a NamedList
where the keys are "field_a" and "field_b", but then my values are
strings, e.g., "{min=500,max=10000,steepness=0.5}".

Anyone who could dash off a quick example of how to do this?

Thanks,
--jay