Set WM_CLASS to org-jabref-JabRefMain

WM_CLASS is used by certain Un*x window managers, such as GNOME, to map windows
to the corresponding application. Currently WM_CLASS is set to java-lang-Thread
which is very generic and not unique to JabRef. Instead, use reflection to set
it to org-jabref-JabRefMain which resembles the main class name.

CHANGELOG.md

@@ -17,6 +17,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - Updated French translation
 - We added support for pasting entries in different formats [#3143](https://github.com/JabRef/jabref/issues/3143)
 - Crossreferenced entries are now used when a BibTex key is generated for an entry with empty fields. [#2811](https://github.com/JabRef/jabref/issues/2811)
+- We now set the WM_CLASS of the UI to org-jabref-JabRefMain to allow certain Un*x window managers to properly identify its windows
 
 ### Fixed
  - We fixed an issue where JabRef would not terminated after asking to collect anonymous statistics [#2955 comment](https://github.com/JabRef/jabref/issues/2955#issuecomment-334591123)

src/main/java/org/jabref/gui/GUIGlobals.java

@@ -2,6 +2,7 @@
 
 import java.awt.Color;
 import java.awt.Font;
+import java.awt.Toolkit;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -156,6 +157,16 @@ public static void init() {
         GUIGlobals.currentFont = new Font(Globals.prefs.get(JabRefPreferences.FONT_FAMILY),
                 Globals.prefs.getInt(JabRefPreferences.FONT_STYLE), Globals.prefs.getInt(JabRefPreferences.FONT_SIZE));
 
+        // Set WM_CLASS using reflection for certain Un*x window managers
+        try {
+            Toolkit xToolkit = Toolkit.getDefaultToolkit();
+            java.lang.reflect.Field awtAppClassNameField = xToolkit.getClass().getDeclaredField("awtAppClassName");
+            awtAppClassNameField.setAccessible(true);
+            awtAppClassNameField.set(xToolkit, "org-jabref-JabRefMain");
+        } catch (Exception e) {
+            // ignore any error since this code only works for certain toolkits
+        }
+
     }
 
     public static void setFont(int size) {