Refactor of DOI import failure dialog, import format reader and clipboard manager

src/main/java/org/jabref/gui/mergeentries/FetchAndMergeEntry.java

@@ -76,7 +76,17 @@ public void fetchAndMerge(BibEntry entry, List<Field> fields) {
                                   })
                                   .onFailure(exception -> {
                                       LOGGER.error("Error while fetching bibliographic information", exception);
-                                      dialogService.showErrorDialogAndWait(exception);
+                                      String localMessage = exception.getCause().getLocalizedMessage();
+                                      // client error
+                                      if (localMessage.startsWith("Client")) {
+                                          dialogService.showInformationDialogAndWait(Localization.lang("Lookup DOI"), Localization.lang("No DOI data exists"));
+                                      // server error
+                                      } else if (localMessage.startsWith("Server")) {
+                                          dialogService.showInformationDialogAndWait(Localization.lang("Lookup DOI"), Localization.lang("DOI server not available"));
+                                      // default error
+                                      } else {
+                                          dialogService.showErrorDialogAndWait(exception);
+                                      }
                                   })
                                   .executeWith(Globals.TASK_EXECUTOR);
                 }

src/main/java/org/jabref/logic/net/URLDownload.java

@@ -40,6 +40,7 @@
 import javax.net.ssl.TrustManager;
 import javax.net.ssl.X509TrustManager;
 
+import org.jabref.logic.l10n.Localization;
 import org.jabref.logic.util.io.FileUtil;
 import org.jabref.model.util.FileHelper;
 
@@ -360,6 +361,14 @@ private URLConnection openConnection() throws IOException {
                     connection = new URLDownload(newUrl).openConnection();
                 }
             }
+            // status code 4xx
+            if (status > HttpURLConnection.HTTP_BAD_REQUEST && status < HttpURLConnection.HTTP_INTERNAL_ERROR) {
+                throw new IOException(Localization.lang("Client Error " + status));
+
+                // status code 5xx
+            } else if (status >= HttpURLConnection.HTTP_INTERNAL_ERROR) {
+                throw new IOException(Localization.lang("Server Error " + status));
+            }
         }
 
         // this does network i/o: GET + read returned headers

src/test/java/org/jabref/logic/net/URLDownloadTest.java

@@ -28,6 +28,22 @@ public void testStringDownloadWithSetEncoding() throws IOException {
         assertTrue(dl.asString().contains("Google"), "google.com should contain google");
     }
 
+    // test client error 404
+    @Test
+    public void testStringDownloadThrowClientError() throws IOException {
+        URLDownload dl = new URLDownload(new URL("http://httpstat.us/404"));
+        IOException exception = assertThrows(IOException.class, dl::asString);
+        assertTrue(exception.getLocalizedMessage().contentEquals("Client Error 404"), "Should be Client Error.");
+    }
+
+    // test server error 503
+    @Test
+    public void testStringDownloadThrowServerError() throws IOException {
+        URLDownload dl = new URLDownload(new URL("http://httpstat.us/503"));
+        IOException exception = assertThrows(IOException.class, dl::asString);
+        assertTrue(exception.getLocalizedMessage().contentEquals("Server Error 503"), "Should be Server Error.");
+    }
+
     @Test
     public void testStringDownload() throws IOException {
         URLDownload dl = new URLDownload(new URL("http://www.google.com"));