Fix lucence segment error by checking for existing index (#8401)

* Fix lucence segment error by checking for exisitng index

fix some potential resource leaks

* Remove empty lines and improve Logger call

Co-authored-by: Oliver Kopp <kopp.dev@gmail.com>

CHANGELOG.md

@@ -20,6 +20,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 
 ### Fixed
 
+- We fixed an issue where the fulltext search on an empty library with no documents would lead to an exception [koppor#522](https://github.com/koppor/jabref/issues/522)
 - We fixed an issue where clicking on "Accept changes" in the merge dialog would lead to an exception [forum#2418](https://discourse.jabref.org/t/the-library-has-been-modified-by-another-program/2418/8)
 - We fixed an issue where clicking on headings in the entry preview could lead to an exception. [#8292](https://github.com/JabRef/jabref/issues/8292)
 - We fixed an issue where IntegrityCheck used the system's character encoding instead of the one set by the library or in preferences [#8022](https://github.com/JabRef/jabref/issues/8022)

src/main/java/org/jabref/logic/pdf/search/indexing/PdfIndexer.java

@@ -59,9 +59,8 @@ public static PdfIndexer of(BibDatabaseContext databaseContext, FilePreferences
      */
     public void createIndex() {
         // Create new index by creating IndexWriter but not writing anything.
-        try {
-            IndexWriter indexWriter = new IndexWriter(directoryToIndex, new IndexWriterConfig(new EnglishStemAnalyzer()).setOpenMode(IndexWriterConfig.OpenMode.CREATE));
-            indexWriter.close();
+        try (IndexWriter indexWriter = new IndexWriter(directoryToIndex, new IndexWriterConfig(new EnglishStemAnalyzer()).setOpenMode(IndexWriterConfig.OpenMode.CREATE))) {
+            // empty comment for checkstyle
         } catch (IOException e) {
             LOGGER.warn("Could not create new Index!", e);
         }
@@ -119,8 +118,7 @@ public void removeFromIndex(BibEntry entry, LinkedFile linkedFile) {
         try (IndexWriter indexWriter = new IndexWriter(
                 directoryToIndex,
                 new IndexWriterConfig(
-                        new EnglishStemAnalyzer()).setOpenMode(IndexWriterConfig.OpenMode.CREATE_OR_APPEND))
-        ) {
+                        new EnglishStemAnalyzer()).setOpenMode(IndexWriterConfig.OpenMode.CREATE_OR_APPEND))) {
             if (!entry.getFiles().isEmpty()) {
                 indexWriter.deleteDocuments(new Term(SearchFieldConstants.PATH, linkedFile.getLink()));
             }
@@ -189,8 +187,7 @@ private void writeToIndex(BibEntry entry, LinkedFile linkedFile) {
         }
         try {
             // Check if a document with this path is already in the index
-            try {
-                IndexReader reader = DirectoryReader.open(directoryToIndex);
+            try (IndexReader reader = DirectoryReader.open(directoryToIndex)) {
                 IndexSearcher searcher = new IndexSearcher(reader);
                 TermQuery query = new TermQuery(new Term(SearchFieldConstants.PATH, linkedFile.getLink()));
                 TopDocs topDocs = searcher.search(query, 1);
@@ -205,19 +202,18 @@ private void writeToIndex(BibEntry entry, LinkedFile linkedFile) {
                         return;
                     }
                 }
-                reader.close();
             } catch (IndexNotFoundException e) {
                 // if there is no index yet, don't need to check anything!
             }
             // If no document was found, add the new one
             Optional<List<Document>> pages = new DocumentReader(entry, filePreferences).readLinkedPdf(this.databaseContext, linkedFile);
             if (pages.isPresent()) {
-                IndexWriter indexWriter = new IndexWriter(directoryToIndex,
-                        new IndexWriterConfig(
-                                new EnglishStemAnalyzer()).setOpenMode(IndexWriterConfig.OpenMode.CREATE_OR_APPEND));
-                indexWriter.addDocuments(pages.get());
-                indexWriter.commit();
-                indexWriter.close();
+                try (IndexWriter indexWriter = new IndexWriter(directoryToIndex,
+                                                               new IndexWriterConfig(
+                                                                                     new EnglishStemAnalyzer()).setOpenMode(IndexWriterConfig.OpenMode.CREATE_OR_APPEND))) {
+                    indexWriter.addDocuments(pages.get());
+                    indexWriter.commit();
+                }
             }
         } catch (IOException e) {
             LOGGER.warn("Could not add the document {} to the index!", linkedFile.getLink(), e);

src/main/java/org/jabref/logic/pdf/search/retrieval/PdfSearcher.java

@@ -49,18 +49,22 @@ public static PdfSearcher of(BibDatabaseContext databaseContext) throws IOExcept
      * @return a result set of all documents that have matches in any fields
      */
     public PdfSearchResults search(final String searchString, final int maxHits)
-            throws IOException {
+        throws IOException {
         if (StringUtil.isBlank(Objects.requireNonNull(searchString, "The search string was null!"))) {
             return new PdfSearchResults();
         }
         if (maxHits <= 0) {
             throw new IllegalArgumentException("Must be called with at least 1 maxHits, was" + maxHits);
         }
 
-        try {
-            List<SearchResult> resultDocs = new LinkedList<>();
+        List<SearchResult> resultDocs = new LinkedList<>();
 
-            IndexReader reader = DirectoryReader.open(indexDirectory);
+        if (!DirectoryReader.indexExists(indexDirectory)) {
+            LOGGER.debug("Index directory {} does not yet exist", indexDirectory);
+            return new PdfSearchResults();
+        }
+
+        try (IndexReader reader = DirectoryReader.open(indexDirectory)) {
             IndexSearcher searcher = new IndexSearcher(reader);
             Query query = new MultiFieldQueryParser(PDF_FIELDS, new EnglishStemAnalyzer()).parse(searchString);
             TopDocs results = searcher.search(query, maxHits);
@@ -69,7 +73,7 @@ public PdfSearchResults search(final String searchString, final int maxHits)
             }
             return new PdfSearchResults(resultDocs);
         } catch (ParseException e) {
-            LOGGER.warn("Could not parse query: '" + searchString + "'! \n" + e.getMessage());
+            LOGGER.warn("Could not parse query: '{}'!\n{}", searchString, e.getMessage());
             return new PdfSearchResults();
         }
     }