Fixes issue JabRef#6851

	Fixes issue preventing files from being drag & dropped into an
	empty library

	Added a drag/drop handlers on the table-view to allow for files
	to be drag & drop into an empty library

CHANGELOG.md

@@ -203,6 +203,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 
 ### Fixed
 
+- We fixed an issue preventing files from being drag & dropeed into an empty library. [#6851](https://github.com/JabRef/jabref/issues/6851) 
 - We fixed an issue where entry preview tab has no name in drop down list. [#6591](https://github.com/JabRef/jabref/issues/6591)
 - We fixed to only search file links in the BIB file location directory when preferences has corresponding checkbox checked. [#5891](https://github.com/JabRef/jabref/issues/5891)
 - We fixed wrong button order (Apply and Cancel) in ManageProtectedTermsDialog.

src/main/java/org/jabref/gui/maintable/MainTable.java

@@ -94,6 +94,9 @@ public MainTable(MainTableDataModel model,
 
         localDragboard = stateManager.getLocalDragboard();
 
+        this.setOnDragOver(this::handleOnDragOverTableView);
+        this.setOnDragDropped(this::handleOnDragDroppedTableView);
+
         this.getColumns().addAll(
                 new MainTableColumnFactory(
                         database,
@@ -174,8 +177,7 @@ public MainTable(MainTableDataModel model,
     }
 
     /**
-     * This is called, if a user starts typing some characters into the keyboard with focus on main table. The {@link
-     * MainTable} will scroll to the cell with the same starting column value and typed string
+     * This is called, if a user starts typing some characters into the keyboard with focus on main table. The {@link MainTable} will scroll to the cell with the same starting column value and typed string
      *
      * @param sortedColumn The sorted column in {@link MainTable}
      * @param keyEvent     The pressed character
@@ -311,6 +313,13 @@ private void handleOnDragOver(TableRow<BibEntryTableViewModel> row, BibEntryTabl
         event.consume();
     }
 
+    private void handleOnDragOverTableView(DragEvent event) {
+        if (event.getDragboard().hasFiles()) {
+            event.acceptTransferModes(TransferMode.ANY);
+        }
+        event.consume();
+    }
+
     private void handleOnDragEntered(TableRow<BibEntryTableViewModel> row, BibEntryTableViewModel entry, MouseDragEvent event) {
         // Support the following gesture to select entries: click on one row -> hold mouse button -> move over other rows
         // We need to select all items between the starting row and the row where the user currently hovers the mouse over
@@ -382,6 +391,20 @@ private void handleOnDragDropped(TableRow<BibEntryTableViewModel> row, BibEntryT
         event.consume();
     }
 
+    private void handleOnDragDroppedTableView(DragEvent event) {
+        boolean success = false;
+
+        if (event.getDragboard().hasFiles()) {
+            List<Path> files = event.getDragboard().getFiles().stream().map(File::toPath).collect(Collectors.toList());
+            importHandler.importFilesInBackground(files).executeWith(Globals.TASK_EXECUTOR);
+
+            success = true;
+        }
+
+        event.setDropCompleted(success);
+        event.consume();
+    }
+
     public void addSelectionListener(ListChangeListener<? super BibEntryTableViewModel> listener) {
         getSelectionModel().getSelectedItems().addListener(listener);
     }