I Don't have experience in writing RequestHandler and I Don't know how difficult it is.
If your requirement is to add more filters to the existing the query, I think it is easy to write a SearchComponent.
You can write a CustomComponent extending SearchComponent. In that Custom component, you can override the prepare method as below:
public void prepare(ResponseBuilder responseBuilder) throws IOException {
BooleanFilter booleanFilter = new BooleanFilter();
TermsFilter termFilter = new TermsFilter(new Term("name", value));
booleanFilter.add(new FilterClause(termFilter, Occur.MUST));
/*
Create a filtered Query with the with the filter created and the actual query
*/
FilteredQuery query = new FilteredQuery(responseBuilder.getQuery(),booleanFilter);
// Set the new query into the response builder.
responseBuilder.setQuery(query);
}
Once you have search component ready, you can create the searchComponent in solrConfig.xml
as below:
<searchComponent name="customComponent" class="com.CustomComponent">
<lst name="parameterName">
<str name="key">value</str>
</lst>
</searchComponent>
Then You can add this as a last component in the existing Request Handler
<arr name="last-components">
<str>customComponent</str>
<str>spellcheck</str>
</arr>