Fix similar error that can be caused by an invalid custom mailer class

Author: HoussemNasri

java/code/src/com/redhat/rhn/domain/notification/UserNotificationFactory.java

@@ -78,7 +78,7 @@ private static void configureMailer() {
             mailer = cobj.getDeclaredConstructor().newInstance();
         }
         catch (Throwable e) {
-            log.warn("An exception was thrown while configuring Mailer", e);
+            log.error("An exception was thrown while initializing custom mailer class", e);
             mailer = new SmtpMail();
         }
     }

java/code/src/com/redhat/rhn/frontend/events/BaseMailAction.java

@@ -52,16 +52,16 @@ public void execute(EventMessage msg) {
      * @return the mailer associated with this class
      */
     protected Mail getMail() {
-        String clazz = Config.get().getString(
-                "web.mailer_class");
+        String clazz = Config.get().getString("web.mailer_class");
         if (clazz == null) {
             return new SmtpMail();
         }
         try {
-            Class cobj = Class.forName(clazz);
-            return (Mail) cobj.newInstance();
+            Class<? extends Mail> cobj = Class.forName(clazz).asSubclass(Mail.class);
+            return cobj.getDeclaredConstructor().newInstance();
         }
-        catch (Exception e) {
+        catch (Throwable e) {
+            getLogger().error("An exception was thrown while initializing custom mailer class", e);
             return new SmtpMail();
         }
     }