Common terms query parser plugin for Apache Solr

Common terms query parser plugin for Apache Solr

/**
 * Solr query parser login for the lucene common terms query. Must be used like q={!commonTermsQueryParser}WeightThe weight...
 * where commonTermsQueryParser is configured in solrconfig.xml.
 *
 * The query field must be given as query parameter "qf". The maxTermFrequency can be configured in solrconfig.xml
 * (default is 0.01). The query is executed against the field given in the request parameter qf while
 * using the query analyzers of this field. 
 *
 * see http://java.dzone.com/articles/create-custom-solr-queryparser
 */
public class CommonTermsQParserPlugin extends QParserPlugin {

    private static final String MAX_TERM_FREQUENCY_CONFIG_PARAM_NAME = "maxTermFrequency";
    private static final float DEFAULT_MAX_TERM_FREQUENCY = 0.01F;

    private float maxTermFrequency = DEFAULT_MAX_TERM_FREQUENCY;

    @Override
    public void init(NamedList args) {
        SolrParams params = SolrParams.toSolrParams(args);

        // handle configuration parameters passed through solrconfig.xml
        final Float maxTermFrequency = params.getFloat(MAX_TERM_FREQUENCY_CONFIG_PARAM_NAME);
        if (maxTermFrequency != null) {
            this.maxTermFrequency = maxTermFrequency;
        }
    }

    @Override
    public QParser createParser(final String queryString, SolrParams localParams, SolrParams params, SolrQueryRequest req) {
        return new QParser(queryString, localParams, params, req) {

            @Override
            public Query parse() throws SyntaxError {
                String queryField = params.get("qf");
                final Analyzer analyzer = req.getSchema().getQueryAnalyzer();
                final CommonTermsQuery commonTermsQuery = new CommonTermsQuery(BooleanClause.Occur.SHOULD, BooleanClause.Occur.SHOULD, maxTermFrequency);
                try {
                    final TokenStream tokenStream = analyzer.tokenStream(queryField, new StringReader(queryString));
                    tokenStream.reset();

                    final CharTermAttribute charTermAttribute = tokenStream.addAttribute(CharTermAttribute.class);
                    while (tokenStream.incrementToken()) {
                        commonTermsQuery.add(new Term(queryField, charTermAttribute.toString()));
                    }
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }

                return commonTermsQuery;
            }
        };
    }
}

solrconfig.xml snippet

    <queryParser class="....CommonTermsQParserPlugin" name="commonTermsQueryParser">
        <float name="maxTermFrequency">0.00001</float>
    </queryParser>