Add support of LuceneSail#SIMILARITY_CLASS_KEY

- add getter/setter for Similarity algorithm instance

Signed-off-by: Jacek Grzebyta <grzebyta.dev@gmail.com>

Author: jgrzebyta

core/sail/fts/lucene-api/src/main/java/org/eclipse/rdf4j/sail/lucene/LuceneSail.java

@@ -196,9 +196,9 @@ public class LuceneSail extends NotifyingSailWrapper {
 	final private Logger logger = LoggerFactory.getLogger(this.getClass());
 
 	/**
-	 * Set the parameter "reindexQuery=" to configure the statements to index over. Default value is
-	 * "SELECT ?s ?p ?o ?c WHERE {{?s ?p ?o} UNION {GRAPH ?c {?s ?p ?o.}}} ORDER BY ?s" . NB: the query must
-	 * contain the bindings ?s, ?p, ?o and ?c and must be ordered by ?s.
+	 * Set the parameter "reindexQuery=" to configure the statements to index over. Default value is "SELECT
+	 * ?s ?p ?o ?c WHERE {{?s ?p ?o} UNION {GRAPH ?c {?s ?p ?o.}}} ORDER BY ?s" . NB: the query must contain
+	 * the bindings ?s, ?p, ?o and ?c and must be ordered by ?s.
 	 */
 	public static final String REINDEX_QUERY_KEY = "reindexQuery";
 
@@ -249,6 +249,12 @@ public class LuceneSail extends NotifyingSailWrapper {
 	 */
 	public static final String ANALYZER_CLASS_KEY = "analyzer";
 
+	/**
+	 * Set this key as sail parameter to configure {@link org.apache.lucene.search.similarities.Similarity}
+	 * class implementation to use for text analysis.
+	 */
+	public static final String SIMILARITY_CLASS_KEY = "similarity";
+
 	/**
 	 * Set this key as sail parameter to influence whether incomplete queries are treated as failure
 	 * (Malformed queries) or whether they are ignored. Set to either "true" or "false". When ommitted in the
@@ -598,8 +604,7 @@ public Statement mapStatement(Statement statement) {
 	}
 
 	protected Collection<SearchQueryInterpreter> getSearchQueryInterpreters() {
-		return Arrays.<SearchQueryInterpreter> asList(
-				new QuerySpecBuilder(incompleteQueryFails),
+		return Arrays.<SearchQueryInterpreter> asList(new QuerySpecBuilder(incompleteQueryFails),
 				new DistanceQuerySpecBuilder(luceneIndex), new GeoRelationQuerySpecBuilder(luceneIndex));
 	}
 }

core/sail/fts/lucene/src/main/java/org/eclipse/rdf4j/sail/lucene/LuceneIndex.java

@@ -87,6 +87,8 @@
 import com.spatial4j.core.context.SpatialContextFactory;
 import com.spatial4j.core.shape.Point;
 import com.spatial4j.core.shape.Shape;
+import org.apache.lucene.search.similarities.DefaultSimilarity;
+import org.apache.lucene.search.similarities.Similarity;
 
 /**
  * A LuceneIndex is a one-stop-shop abstraction of a Lucene index. It takes care of proper synchronization of
@@ -118,6 +120,8 @@ public class LuceneIndex extends AbstractLuceneIndex {
 
 	private volatile Analyzer queryAnalyzer;
 
+	private volatile Similarity similarity;
+
 	/**
 	 * The IndexWriter that can be used to alter the index' contents. Created lazily.
 	 */
@@ -162,6 +166,7 @@ public synchronized void initialize(Properties parameters)
 		super.initialize(parameters);
 		this.directory = createDirectory(parameters);
 		this.analyzer = createAnalyzer(parameters);
+		this.similarity = createSimilarity(parameters);
 		// slightly hacky cast to cope with the fact that Properties is
 		// Map<Object,Object>
 		// even though it is effectively Map<String,String>
@@ -203,6 +208,21 @@ protected Analyzer createAnalyzer(Properties parameters)
 		return analyzer;
 	}
 
+	protected Similarity createSimilarity(Properties parameters)
+		throws Exception
+	{
+		Similarity similarity;
+		if (parameters.containsKey(LuceneSail.SIMILARITY_CLASS_KEY)) {
+			similarity = (Similarity)Class.forName(
+					parameters.getProperty(LuceneSail.SIMILARITY_CLASS_KEY)).newInstance();
+		}
+		else {
+			similarity = new DefaultSimilarity();
+		}
+
+		return similarity;
+	}
+
 	private void postInit()
 		throws IOException
 	{
@@ -212,6 +232,7 @@ private void postInit()
 		if (!DirectoryReader.indexExists(directory)) {
 			logger.debug("creating new Lucene index in directory {}", directory);
 			IndexWriterConfig indexWriterConfig = new IndexWriterConfig(analyzer);
+			indexWriterConfig.setSimilarity(similarity);
 			indexWriterConfig.setOpenMode(OpenMode.CREATE);
 			IndexWriter writer = new IndexWriter(directory, indexWriterConfig);
 			writer.close();
@@ -274,7 +295,9 @@ public synchronized IndexSearcher getIndexSearcher()
 		if (closed.get()) {
 			throw new SailException("Index has been closed");
 		}
-		return getCurrentMonitor().getIndexSearcher();
+		IndexSearcher indexSearcher = getCurrentMonitor().getIndexSearcher();
+		indexSearcher.setSimilarity(similarity);
+		return indexSearcher;
 	}
 
 	/**