Hybrid Search Using a Custom Algorithm in Apache Solr

				
					package org.apache.solr.handler.component.combine;

import java.util.List;
import java.util.Map;
import org.apache.lucene.search.Explanation;
import org.apache.solr.common.params.SolrParams;
import org.apache.solr.common.util.NamedList;
import org.apache.solr.common.util.SimpleOrderedMap;
import org.apache.solr.handler.component.ShardDoc;

/**
 * Example implementation of a custom combiner plugin.
 * This class can be used as a template for developing a custom combiner.
 * NOTE: This implementation intentionally does not perform real merging logic.
 * It is only meant as a minimal reference template for plugin development.
 */

public class CustomCombiner extends QueryAndResponseCombiner {

    /** Example parameter loaded from solrconfig.xml */
    private int customInt;

    /**
     * Called once at Solr startup when the plugin is created.
     * Here we read parameters defined inside the <combiner> configuration.
     */
    @Override
    public void init(NamedList<?> args) {
        Object customParam = args.get("customParam");
        if (customParam != null) {
            this.customInt = Integer.parseInt(customParam.toString());
        }
    }

    public int getCustomInt() {
        return customInt;
    }

    /**
     * This is the core method of the combiner.
     * Here is where the developer should implement the merging algorithm:
     * The returned list becomes the final ranked result returned by Solr.
     * NOTE: This example returns an empty list intentionally.
     */
    @Override
    public List<ShardDoc> combine(Map<String, List<ShardDoc>> shardDocMap, SolrParams solrParams) {
        return List.of();
    }


    /**
     * Debug/explain information.
     * This method allows the combiner to expose how the final ranking
     * was produced. The information is returned when debugQuery=true.
     * A real implementation would normally add per-document explanations.
     */
    @Override
    public SimpleOrderedMap<Explanation> getExplanations(
            String[] queryKeys,
            Map<String, List<ShardDoc>> queriesDocMap,
            List<ShardDoc> combinedQueriesDocs,
            SolrParams solrParams) {
        SimpleOrderedMap<Explanation> docIdsExplanations = new SimpleOrderedMap<>();
        docIdsExplanations.add("combinerDetails", Explanation.match(customInt, "This is a test for custom combiner"));
        return docIdsExplanations;
    }
}