Explainer.java

package lia.searching;

/**
 * Copyright Manning Publications Co.
 *
 * Licensed 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 lan      
*/

import org.apache.lucene.analysis.SimpleAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.queryParser.QueryParser;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.store.Directory;
import org.apache.lucene.util.Version;

import java.io.File;

// From chapter 3
public class Explainer {
  public static void main(String[] args) throws Exception {
    if (args.length != 2) {
      System.err.println("Usage: Explainer <index dir> <query>");
      System.exit(1);
    }

    String indexDir = args[0];
    String queryExpression = args[1];

    Directory directory = FSDirectory.open(new File(indexDir));
    QueryParser parser = new QueryParser(Version.LUCENE_30,
                                         "contents", new SimpleAnalyzer());
    Query query = parser.parse(queryExpression);

    System.out.println("Query: " + queryExpression);

    IndexSearcher searcher = new IndexSearcher(directory);
    TopDocs topDocs = searcher.search(query, 10);

    for (ScoreDoc match : topDocs.scoreDocs) {
      Explanation explanation
         = searcher.explain(query, match.doc);     //#A

      System.out.println("----------");
      Document doc = searcher.doc(match.doc);
      System.out.println(doc.get("title"));
      System.out.println(explanation.toString());  //#B
    }
    searcher.close();
    directory.close();
  }
}
/*
#A Generate Explanation
#B Output Explanation
*/