Fix: Allow pasting PDF URLs into main table to create entries (JabRef#12911)

* Improve handling of PDF file import behavior

* Add support for handling PDF URLs when pasted

* Revert submodule changes

* Replace Collections.emptyList() with List.of() and improve exception handling

* Change log level from debug to trace for PDF URL

* Registered fix in changelog

* Used getValidFileName for helper method deriveFileNameFromUrl

* Refactor PDF URL detection using FileUtil.isPDFFile

* Move getFileNameFromURL helper method to URLUtil class

Author: Kaan0029

CHANGELOG.md

@@ -105,6 +105,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 - We fixed an issue where valid DOI could not be imported if it had special characters like `<` or `>`. [#12434](https://github.com/JabRef/jabref/issues/12434)
 - We fixed an issue where the tooltip only displayed the first linked file when hovering. [#12470](https://github.com/JabRef/jabref/issues/12470)
 - We fixed an issue where some texts in the "Citation Information" tab and the "Preferences" dialog could not be translated. [#12883](https://github.com/JabRef/jabref/pull/12883)
+- We fixed an issue where pasting a PDF URL into the main table caused an import error instead of creating a new entry. [#12911](https://github.com/JabRef/jabref/pull/12911)
 - We fixed an issue where libraries would sometimes be hidden when closing tabs with the Welcome tab open. [#12894](https://github.com/JabRef/jabref/issues/12894)
 
 ### Removed

src/main/java/org/jabref/gui/externalfiles/ImportHandler.java

@@ -38,9 +38,13 @@
 import org.jabref.logic.importer.ParseException;
 import org.jabref.logic.importer.ParserResult;
 import org.jabref.logic.importer.fileformat.BibtexParser;
+import org.jabref.logic.importer.fileformat.PdfMergeMetadataImporter;
 import org.jabref.logic.l10n.Localization;
+import org.jabref.logic.net.URLDownload;
 import org.jabref.logic.util.BackgroundTask;
+import org.jabref.logic.util.StandardFileType;
 import org.jabref.logic.util.TaskExecutor;
+import org.jabref.logic.util.URLUtil;
 import org.jabref.logic.util.UpdateField;
 import org.jabref.logic.util.io.FileUtil;
 import org.jabref.model.FieldChange;
@@ -371,7 +375,7 @@ public List<BibEntry> handleBibTeXData(String entries) {
             return result;
         } catch (ParseException ex) {
             LOGGER.error("Could not paste", ex);
-            return Collections.emptyList();
+            return List.of();
         }
     }
 
@@ -397,7 +401,20 @@ public void importStringConstantsWithDuplicateCheck(Collection<BibtexString> str
 
     public List<BibEntry> handleStringData(String data) throws FetcherException {
         if ((data == null) || data.isEmpty()) {
-            return Collections.emptyList();
+            return List.of();
+        }
+        LOGGER.trace("Checking if URL is a PDF: {}", data);
+
+        if (URLUtil.isURL(data)) {
+            String fileName = data.substring(data.lastIndexOf('/') + 1);
+            if (FileUtil.isPDFFile(Path.of(fileName))) {
+                try {
+                    return handlePdfUrl(data);
+                } catch (IOException ex) {
+                    LOGGER.error("Could not handle PDF URL", ex);
+                    return List.of();
+                }
+            }
         }
 
         if (!CompositeIdFetcher.containsValidId(data)) {
@@ -421,7 +438,7 @@ private List<BibEntry> tryImportFormats(String data) {
             return unknownFormatImport.parserResult().getDatabase().getEntries();
         } catch (ImportException ex) { // ex is already localized
             dialogService.showErrorDialogAndWait(Localization.lang("Import error"), ex);
-            return Collections.emptyList();
+            return List.of();
         }
     }
 
@@ -444,4 +461,44 @@ public void importEntriesWithDuplicateCheck(BibDatabaseContext database, List<Bi
             }
         }
     }
+
+    private List<BibEntry> handlePdfUrl(String pdfUrl) throws IOException {
+        Optional<Path> targetDirectory = bibDatabaseContext.getFirstExistingFileDir(preferences.getFilePreferences());
+        if (targetDirectory.isEmpty()) {
+            LOGGER.warn("File directory not available while downloading {}.", pdfUrl);
+            return List.of();
+        }
+        URLDownload urlDownload = new URLDownload(pdfUrl);
+        String filename = URLUtil.getFileNameFromUrl(pdfUrl);
+        Path targetFile = targetDirectory.get().resolve(filename);
+        try {
+            urlDownload.toFile(targetFile);
+        } catch (FetcherException fe) {
+            LOGGER.error("Error downloading PDF from URL", fe);
+            return List.of();
+        }
+        try {
+            PdfMergeMetadataImporter importer = new PdfMergeMetadataImporter(preferences.getImportFormatPreferences());
+            ParserResult parserResult = importer.importDatabase(targetFile, bibDatabaseContext, preferences.getFilePreferences());
+            if (parserResult.hasWarnings()) {
+                LOGGER.warn("PDF import had warnings: {}", parserResult.getErrorMessage());
+            }
+            List<BibEntry> entries = parserResult.getDatabase().getEntries();
+            if (!entries.isEmpty()) {
+                entries.forEach(entry -> {
+                    if (entry.getFiles().isEmpty()) {
+                        entry.addFile(new LinkedFile("", targetFile, StandardFileType.PDF.getName()));
+                    }
+                });
+            } else {
+                BibEntry emptyEntry = new BibEntry();
+                emptyEntry.addFile(new LinkedFile("", targetFile, StandardFileType.PDF.getName()));
+                entries.add(emptyEntry);
+            }
+            return entries;
+        } catch (IOException ex) {
+            LOGGER.error("Error importing PDF from URL - IO issue", ex);
+            return List.of();
+        }
+    }
 }

src/main/java/org/jabref/logic/util/URLUtil.java

@@ -9,6 +9,8 @@
 import java.util.Objects;
 import java.util.regex.Pattern;
 
+import org.jabref.logic.util.io.FileUtil;
+
 /**
  * URL utilities for URLs in the JabRef logic.
  * <p>
@@ -122,4 +124,19 @@ public static URI createUri(String url) {
             throw new IllegalArgumentException(e);
         }
     }
+
+    /**
+     * Extracts the filename from a URL.
+     * If the URL doesn't have a filename (ends with '/'), returns a default name.
+     *
+     * @param url the URL string to extract the filename from
+     * @return the extracted filename or a default name if none found
+     */
+    public static String getFileNameFromUrl(String url) {
+        String fileName = url.substring(url.lastIndexOf('/') + 1);
+        if (fileName.isBlank()) {
+            fileName = "downloaded.pdf";
+        }
+        return FileUtil.getValidFileName(fileName);
+    }
 }