Fix opening pdf with okular in linux (#5253) (#5855)

* Fix opening pdf with okular in linux (#5253)

* Fix opening pdf with okular in linux (#5253) stream ouput to Logger

* Fix checkstyle

Co-authored-by: Tobias Diez <tobiasdiez@gmx.de>

Author: t-morales

CHANGELOG.md

@@ -18,6 +18,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 
 ### Fixed
 
+- We fixed and issue where pdf files will not open under some KDE linux distributions when using okular. [#5253](https://github.com/JabRef/jabref/issues/5253)
 - We fixed an issue where the Medline fetcher was only working when JabRef was running from source. [#5645](https://github.com/JabRef/jabref/issues/5645)
 - We fixed some visual issues in the dark theme. [#5764](https://github.com/JabRef/jabref/pull/5764) [#5753](https://github.com/JabRef/jabref/issues/5753)
 - We fixed an issue where non-default previews didn't handle unicode characters. [#5779](https://github.com/JabRef/jabref/issues/5779)

src/main/java/org/jabref/gui/desktop/os/Linux.java

@@ -15,10 +15,15 @@
 import org.jabref.gui.externalfiletype.ExternalFileTypes;
 import org.jabref.preferences.JabRefPreferences;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import static org.jabref.preferences.JabRefPreferences.ADOBE_ACROBAT_COMMAND;
 import static org.jabref.preferences.JabRefPreferences.USE_PDF_READER;
 
 public class Linux implements NativeDesktop {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Linux.class);
+
     @Override
     public void openFile(String filePath, String fileType) throws IOException {
         Optional<ExternalFileType> type = ExternalFileTypes.getInstance().getExternalFileTypeByExt(fileType);
@@ -30,7 +35,13 @@ public void openFile(String filePath, String fileType) throws IOException {
             viewer = "xdg-open";
         }
         String[] cmdArray = { viewer, filePath };
-        Runtime.getRuntime().exec(cmdArray);
+        Process p = Runtime.getRuntime().exec(cmdArray);
+        // When the stream is full at some point, then blocks the execution of the program
+        // See https://stackoverflow.com/questions/10981969/why-is-going-through-geterrorstream-necessary-to-run-a-process.
+        BufferedReader in = new BufferedReader(new InputStreamReader(p.getErrorStream()));
+        String line;
+        line = in.readLine();
+        LOGGER.debug("Received output: " + line);
     }
 
     @Override
@@ -46,7 +57,13 @@ public void openFileWithApplication(String filePath, String application) throws
         String[] cmdArray = new String[openWith.length + 1];
         System.arraycopy(openWith, 0, cmdArray, 0, openWith.length);
         cmdArray[cmdArray.length - 1] = filePath;
-        Runtime.getRuntime().exec(cmdArray);
+        Process p = Runtime.getRuntime().exec(cmdArray);
+        // When the stream is full at some point, then blocks the execution of the program
+        // See https://stackoverflow.com/questions/10981969/why-is-going-through-geterrorstream-necessary-to-run-a-process.
+        BufferedReader in = new BufferedReader(new InputStreamReader(p.getErrorStream()));
+        String line;
+        line = in.readLine();
+        LOGGER.debug("Received output: " + line);
     }
 
     @Override