Added error dialog when setting invalid main file directory (JabRef#1921

)

CHANGELOG.md

@@ -47,6 +47,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - Fixed [#1882](https://github.com/JabRef/jabref/issues/1882): Crash after saving illegal bibtexkey in entry editor
 - Fixed field `location` containing only city is not exported correctly to MS-Office 2007 xml format
 - Fixed field `key` field is not exported to MS-Office 2008 xml format
+- Fixed download files failed silently when an invalid directory is selected
 
 ### Removed
 - The non-supported feature of being able to define file directories for any extension is removed. Still, it should work for older databases using the legacy `ps` and `pdf` fields, although we strongly encourage using the `file` field. 

src/main/java/net/sf/jabref/gui/externalfiles/DownloadExternalFile.java

@@ -215,7 +215,10 @@ public void download(URL url, final DownloadCallback callback) throws IOExceptio
 
                 callback.downloadComplete(fileListEntry);
             } catch (IOException ex) {
-                LOGGER.warn("Problem downloading file", ex);
+                String content = String.format("%s %n %s", Localization.lang("Error message:"),
+                        ex.getLocalizedMessage());
+                JOptionPane.showMessageDialog(this.frame, content,
+                        Localization.lang("Error while writing"), JOptionPane.ERROR_MESSAGE);
             }
 
             if (!tmp.delete()) {

src/main/java/net/sf/jabref/gui/preftabs/FileTab.java

@@ -3,13 +3,17 @@
 import java.awt.BorderLayout;
 import java.awt.Dimension;
 import java.awt.event.ItemListener;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
 
 import javax.swing.BorderFactory;
 import javax.swing.ButtonGroup;
 import javax.swing.JButton;
 import javax.swing.JCheckBox;
 import javax.swing.JComboBox;
 import javax.swing.JLabel;
+import javax.swing.JOptionPane;
 import javax.swing.JPanel;
 import javax.swing.JRadioButton;
 import javax.swing.JSpinner;
@@ -281,7 +285,14 @@ else if (origAutoSaveSetting && !autoSave.isSelected()) {
 
     @Override
     public boolean validateSettings() {
-        return true;
+        Path path = Paths.get(fileDir.getText());
+        boolean valid = Files.exists(path) && Files.isDirectory(path);
+        if (!valid) {
+            String content = String.format("%s -> %s %n %n %s: %n %s", Localization.lang("File"),
+                    Localization.lang("Main file directory"), Localization.lang("Directory not found"), path);
+            JOptionPane.showMessageDialog(this.frame, content, Localization.lang("Error"), JOptionPane.ERROR_MESSAGE);
+        }
+        return valid;
     }
 
     @Override