Fix arXiv fetcher tests (#7686)

* Add some code comments and remove some empty lines

* Fix tests (arXiv does not use https URLs)

* Fix https

* Readbility fixes

Author: koppor

src/main/java/org/jabref/logic/importer/fetcher/ArXiv.java

@@ -16,7 +16,6 @@
 import javax.xml.parsers.DocumentBuilderFactory;
 import javax.xml.parsers.ParserConfigurationException;
 
-import org.jabref.logic.cleanup.CleanupJob;
 import org.jabref.logic.cleanup.EprintCleanup;
 import org.jabref.logic.help.HelpFile;
 import org.jabref.logic.importer.FetcherException;
@@ -80,7 +79,6 @@ public Optional<URL> findFullText(BibEntry entry) throws IOException {
                                                           .map(Optional::get)
                                                           .findFirst();
             pdfUrl.ifPresent(url -> LOGGER.info("Fulltext PDF found @ arXiv."));
-
             return pdfUrl;
         } catch (FetcherException e) {
             LOGGER.warn("arXiv API request failed", e);
@@ -117,11 +115,12 @@ private Optional<ArXivEntry> searchForEntryById(String id) throws FetcherExcepti
         }
     }
 
-    private List<ArXivEntry> searchForEntries(BibEntry entry) throws FetcherException {
-        entry = (BibEntry) entry.clone();
-        CleanupJob cleanupJob = new EprintCleanup();
-        cleanupJob.cleanup(entry);
-        // 1. Eprint
+    private List<ArXivEntry> searchForEntries(BibEntry originalEntry) throws FetcherException {
+        // We need to clone the entry, because we modify it by a cleanup job.
+        final BibEntry entry = (BibEntry) originalEntry.clone();
+
+        // 1. Check for Eprint
+        new EprintCleanup().cleanup(entry);
         Optional<String> identifier = entry.getField(StandardField.EPRINT);
         if (StringUtil.isNotBlank(identifier)) {
             try {
@@ -133,26 +132,21 @@ private List<ArXivEntry> searchForEntries(BibEntry entry) throws FetcherExceptio
         }
 
         // 2. DOI and other fields
-        String query;
-
-        Optional<String> doi = entry.getField(StandardField.DOI).flatMap(DOI::parse).map(DOI::getNormalized);
-        if (doi.isPresent()) {
-            // Search for an entry in the ArXiv which is linked to the doi
-            query = "doi:" + doi.get();
-        } else {
-            Optional<String> authorQuery = entry.getField(StandardField.AUTHOR).map(author -> "au:" + author);
-            Optional<String> titleQuery = entry.getField(StandardField.TITLE).map(title -> "ti:" + StringUtil.ignoreCurlyBracket(title));
-            query = OptionalUtil.toList(authorQuery, titleQuery).stream().collect(Collectors.joining("+AND+"));
-        }
-
+        String query = entry.getField(StandardField.DOI)
+             .flatMap(DOI::parse)
+             .map(DOI::getNormalized)
+             .map(doiString -> "doi:" + doiString)
+             .orElseGet(() -> {
+                 Optional<String> authorQuery = entry.getField(StandardField.AUTHOR).map(author -> "au:" + author);
+                 Optional<String> titleQuery = entry.getField(StandardField.TITLE).map(title -> "ti:" + StringUtil.ignoreCurlyBracket(title));
+                 return String.join("+AND+", OptionalUtil.toList(authorQuery, titleQuery));
+             });
         Optional<ArXivEntry> arxivEntry = searchForEntry(query);
-
         if (arxivEntry.isPresent()) {
             // Check if entry is a match
             StringSimilarity match = new StringSimilarity();
             String arxivTitle = arxivEntry.get().title.orElse("");
             String entryTitle = StringUtil.ignoreCurlyBracket(entry.getField(StandardField.TITLE).orElse(""));
-
             if (match.isSimilar(arxivTitle, entryTitle)) {
                 return OptionalUtil.toList(arxivEntry);
             }
@@ -175,7 +169,7 @@ private List<ArXivEntry> queryApi(String searchQuery, List<ArXivIdentifier> ids,
 
     /**
      * Queries the API.
-     *
+     * <p>
      * If only {@code searchQuery} is given, then the API will return results for each article that matches the query.
      * If only {@code ids} is given, then the API will return results for each article in the list.
      * If both {@code searchQuery} and {@code ids} are given, then the API will return each article in

src/main/java/org/jabref/model/strings/StringUtil.java

@@ -654,7 +654,6 @@ public static String boldHTML(String input) {
      * Return string enclosed in HTML bold tags  if not null, otherwise return alternative text in HTML bold tags
      */
     public static String boldHTML(String input, String alternative) {
-
         if (input == null) {
             return "<b>" + alternative + "</b>";
         }

src/test/java/org/jabref/logic/importer/fetcher/ArXivTest.java

@@ -99,7 +99,7 @@ void findFullTextByTitle() throws IOException {
     void findFullTextByTitleWithCurlyBracket() throws IOException {
         entry.setField(StandardField.TITLE, "Machine versus {Human} {Attention} in {Deep} {Reinforcement} {Learning} {Tasks}");
 
-        assertEquals(Optional.of(new URL("https://arxiv.org/pdf/2010.15942v2")), fetcher.findFullText(entry));
+        assertEquals(Optional.of(new URL("http://arxiv.org/pdf/2010.15942v2")), fetcher.findFullText(entry));
     }
 
     @Test
@@ -131,7 +131,7 @@ void findFullTextByTitleWithCurlyBracketAndPartOfAuthor() throws IOException {
         entry.setField(StandardField.TITLE, "Machine versus {Human} {Attention} in {Deep} {Reinforcement} {Learning} {Tasks}");
         entry.setField(StandardField.AUTHOR, "Zhang, Ruohan and Guo");
 
-        assertEquals(Optional.of(new URL("https://arxiv.org/pdf/2010.15942v2")), fetcher.findFullText(entry));
+        assertEquals(Optional.of(new URL("http://arxiv.org/pdf/2010.15942v2")), fetcher.findFullText(entry));
     }
 
     @Test