c# - How to highlight the searched keyword in Lucene.net?

Question

I have created a Lucene.net Project. I want to highlight the searched keywords.

How can I highlight these keywords using Lucene.net search?

Answer 1

#region search hightligh
        public static IEnumerable<Models.Post> SearchHighligh(string input, string fieldName = "")
        {
            if (string.IsNullOrEmpty(input)) return new List<Models.Post>();

            var terms = input.Trim().Replace("-", " ").Split(' ')
                .Where(x => !string.IsNullOrEmpty(x)).Select(x => x.Trim() + "*");
            input = string.Join(" ", terms);

            return _searchHighligh(input, fieldName);
        }
        private static string getHighlight(Highlighter highlighter, StandardAnalyzer analyzer, string fieldContent)
        {
            Lucene.Net.Analysis.TokenStream stream = analyzer.TokenStream("", new StringReader(fieldContent));
            return highlighter.GetBestFragments(stream, fieldContent, 1, ".");
        }


        private static IEnumerable<Models.Post> _searchHighligh(string searchQuery, string searchField = "")
        {
            // validation
            if (string.IsNullOrEmpty(searchQuery.Replace("*", "").Replace("?", ""))) return new List<Models.Post>();

            // set up lucene searcher
            using (var searcher = new IndexSearcher(_directory, false))
            {
                var hits_limit = 1000;
                var analyzer = new StandardAnalyzer(Lucene.Net.Util.Version.LUCENE_30);

                IFormatter formatter = new SimpleHTMLFormatter("<span style=\"font-weight:bold; background-color:yellow;\">", "</span>");
                SimpleFragmenter fragmenter = new SimpleFragmenter(1000);
                QueryScorer scorer = null;

                ScoreDoc[] hits;
                // search by single field
                if (!string.IsNullOrEmpty(searchField))
                {
                    var parser = new QueryParser(Lucene.Net.Util.Version.LUCENE_30, searchField, analyzer);
                    var query = parseQuery(searchQuery, parser);
                    scorer = new QueryScorer(query);
                    hits = searcher.Search(query, hits_limit).ScoreDocs;

                }
                // search by multiple fields (ordered by RELEVANCE)
                else
                {
                    var parser = new MultiFieldQueryParser
                        (Lucene.Net.Util.Version.LUCENE_30, new[] { "Title", "Body" }, analyzer);
                    var query = parseQuery(searchQuery, parser);
                    scorer = new QueryScorer(query);
                    hits = searcher.Search(query, null, hits_limit, Sort.INDEXORDER).ScoreDocs;

                }
                Highlighter highlighter = new Highlighter(formatter, scorer);
                highlighter.TextFragmenter = fragmenter;
                var results = _mapLuceneToDataListHighligh(hits, searcher, highlighter, analyzer);
                analyzer.Close();
                searcher.Dispose();
                return results;
            }
        }
        private static IEnumerable<Models.Post> _mapLuceneToDataListHighligh(IEnumerable<ScoreDoc> hits, IndexSearcher searcher, Highlighter highlighter, StandardAnalyzer analyzer)
        {
            // v 2.9.4: use 'hit.doc'
            // v 3.0.3: use 'hit.Doc'
            return hits.Select(hit => _mapLuceneDocumentToDataHighligh(searcher.Doc(hit.Doc), highlighter, analyzer)).ToList();
        }
        private static Models.Post _mapLuceneDocumentToDataHighligh(Document doc, Highlighter highlighter, StandardAnalyzer analyzer)
        {
            return new Models.Post
            {
                Id = Convert.ToInt32(doc.Get("Id")),
                //Title = getHighlight(highlighter, analyzer,doc.Get("Title")),
                Title =doc.Get("Title"),
                Body = getHighlight(highlighter, analyzer, doc.Get("Body")),
                SiteId = Convert.ToInt16(doc.Get("SiteId")),
                PostTypeId = Convert.ToInt32(doc.Get("PostTypeId")),
                OwnerUserId = Convert.ToInt32(doc.Get("OwnerUserId")),
                ParentId = Convert.ToInt32(doc.Get("ParentId")),
                CreationDate = UTILS.Function.getDateTime((doc.Get("CreationDate")), "g")
            };
        } 
        #endregion