Lucene 4.3

package com.fox.facet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.lucene.analysis.core.WhitespaceAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.facet.index.FacetFields;
import org.apache.lucene.facet.params.FacetSearchParams;
import org.apache.lucene.facet.search.CountFacetRequest;
import org.apache.lucene.facet.search.DrillDownQuery;
import org.apache.lucene.facet.search.FacetResult;
import org.apache.lucene.facet.search.FacetsCollector;
import org.apache.lucene.facet.taxonomy.CategoryPath;
import org.apache.lucene.facet.taxonomy.TaxonomyReader;
import org.apache.lucene.facet.taxonomy.directory.DirectoryTaxonomyReader;
import org.apache.lucene.facet.taxonomy.directory.DirectoryTaxonomyWriter;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.MatchAllDocsQuery;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;
import org.apache.lucene.util.Version;

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/** Shows simple usage of faceted indexing and search. */
public class SimpleFacetsExample {

    private final Directory indexDir = new RAMDirectory();
    private final Directory taxoDir = new RAMDirectory();

    /** Empty constructor */
    public SimpleFacetsExample() {
    }

    private void add(IndexWriter indexWriter, FacetFields facetFields, String... categoryPaths) throws IOException {
        Document doc = new Document();

        List<CategoryPath> paths = new ArrayList<CategoryPath>();
        for (String categoryPath : categoryPaths) {
            paths.add(new CategoryPath(categoryPath, '/'));
        }
        facetFields.addFields(doc, paths);
        indexWriter.addDocument(doc);
    }

    /** Build the example index. */
    private void index() throws IOException {
        IndexWriter indexWriter = new IndexWriter(indexDir, new IndexWriterConfig(Version.LUCENE_43, new WhitespaceAnalyzer(
                Version.LUCENE_43)));

        // Writes facet ords to a separate directory from the main index
        DirectoryTaxonomyWriter taxoWriter = new DirectoryTaxonomyWriter(taxoDir);

        // Reused across documents, to add the necessary facet fields
        FacetFields facetFields = new FacetFields(taxoWriter);

        add(indexWriter, facetFields, "Author/Bob", "Publish Date/2010/10/15");
        add(indexWriter, facetFields, "Author/Lisa", "Publish Date/2010/10/20");
        add(indexWriter, facetFields, "Author/Lisa", "Publish Date/2012/1/1");
        add(indexWriter, facetFields, "Author/Susan", "Publish Date/2012/1/7");
        add(indexWriter, facetFields, "Author/Frank", "Publish Date/1999/5/5");

        indexWriter.close();
        taxoWriter.close();
    }

    /** User runs a query and counts facets. */
    private List<FacetResult> search() throws IOException {
        DirectoryReader indexReader = DirectoryReader.open(indexDir);
        IndexSearcher searcher = new IndexSearcher(indexReader);
        TaxonomyReader taxoReader = new DirectoryTaxonomyReader(taxoDir);

        // Count both "Publish Date" and "Author" dimensions
        FacetSearchParams fsp = new FacetSearchParams(new CountFacetRequest(new CategoryPath("Publish Date"), 10),
                new CountFacetRequest(new CategoryPath("Author"), 10));

        // Aggregatses the facet counts
        FacetsCollector fc = FacetsCollector.create(fsp, searcher.getIndexReader(), taxoReader);

        // MatchAllDocsQuery is for "browsing" (counts facets
        // for all non-deleted docs in the index); normally
        // you'd use a "normal" query, and use MultiCollector to
        // wrap collecting the "normal" hits and also facets:
        searcher.search(new MatchAllDocsQuery(), fc);

        // Retrieve results
        List<FacetResult> facetResults = fc.getFacetResults();

        indexReader.close();
        taxoReader.close();

        return facetResults;
    }

    /** User drills down on 'Publish Date/2010'. */
    private List<FacetResult> drillDown() throws IOException {
        DirectoryReader indexReader = DirectoryReader.open(indexDir);
        IndexSearcher searcher = new IndexSearcher(indexReader);
        TaxonomyReader taxoReader = new DirectoryTaxonomyReader(taxoDir);

        // Now user drills down on Publish Date/2010:
        FacetSearchParams fsp = new FacetSearchParams(new CountFacetRequest(new CategoryPath("Author"), 10));
        DrillDownQuery q = new DrillDownQuery(fsp.indexingParams, new MatchAllDocsQuery());
        q.add(new CategoryPath("Publish Date/2010", '/'));
        FacetsCollector fc = FacetsCollector.create(fsp, searcher.getIndexReader(), taxoReader);
        searcher.search(q, fc);

        // Retrieve results
        List<FacetResult> facetResults = fc.getFacetResults();

        indexReader.close();
        taxoReader.close();

        return facetResults;
    }

    /** Runs the search example. */
    public List<FacetResult> runSearch() throws IOException {
        index();
        return search();
    }

    /** Runs the drill-down example. */
    public List<FacetResult> runDrillDown() throws IOException {
        index();
        return drillDown();
    }

    /** Runs the search and drill-down examples and prints the results. */
    public static void main(String[] args) throws Exception {
        System.out.println("Facet counting example:");
        System.out.println("-----------------------");
        List<FacetResult> results = new SimpleFacetsExample().runSearch();
        for (FacetResult res : results) {
            System.out.println(res);
        }

        System.out.println("
");
        System.out.println("Facet drill-down example (Publish Date/2010):");
        System.out.println("---------------------------------------------");
        results = new SimpleFacetsExample().runDrillDown();
        for (FacetResult res : results) {
            System.out.println(res);
        }
    }

}

Result:

Facet counting example:
-----------------------
Request: Publish Date nRes=10 nLbl=10
Num valid Descendants (up to specified depth): 3
    Publish Date (0.0)
          Publish Date/2012 (2.0)
          Publish Date/2010 (2.0)
          Publish Date/1999 (1.0)
Request: Author nRes=10 nLbl=10
Num valid Descendants (up to specified depth): 4
    Author (0.0)
          Author/Lisa (2.0)
          Author/Frank (1.0)
          Author/Susan (1.0)
          Author/Bob (1.0)


Facet drill-down example (Publish Date/2010):
---------------------------------------------
Request: Author nRes=10 nLbl=10
Num valid Descendants (up to specified depth): 2
    Author (0.0)
          Author/Lisa (1.0)
          Author/Bob (1.0)