Added @PreserveOnRefresh annotation to prevent Singleton exception

doc/dev_notes.md

@@ -39,9 +39,16 @@ For production:
 ```
 build graalvm binary
 ./gradlew nativeCompile failed, need for some improvements!
-./gradlew nativeCompile -Dvaadin.productionMode=true
+
+1. First build jar, and get META-INF with   
+    ./gradlew clean build -Pvaadin.productionMode -x processTestAot
+    java -agentlib:native-image-agent=config-output-dir=src/main/resources/META-INF/native-image -jar build/libs/ModeratorElection-0.0.1-SNAPSHOT.jar 
+    curl -X GET http://localhost:8080 
+2. graalvm native-image compilation
+    ./gradlew nativeCompile -Dvaadin.productionMode=true //-H:ConfigurationFileDirectories=/path/to/config-dir/ notwendig falls nicht in src/main/resources/META-INF/native-image/
 
 ```
+
 ```
 gu available
 https://docs.oracle.com/en/graalvm/enterprise/21/docs/reference-manual/graalvm-updater/#component-installation
@@ -62,4 +69,14 @@ https://github.com/vaadin/flow/issues/9376
 https://mvysny.github.io/cant-move-node/
 https://vaadin.com/forum/t/unregistered-node-was-not-found-based-on-its-id-the-tree-is-most-likely-co/161068
 https://vaadin.com/docs/v14/flow/integrations/spring/tutorial-spring-scopes
-'''
+    => @PreserveOnRefresh annotation in MainView.java does the trick
+```
+
+```
+pyb test funktionsfähig machen, ddadevops Doku weiss mehr
+erledigt!
+```
+
+```
+ddadevops anpassung, dass src code ins docker image übergeben werden kann - ohne git clone
+```

src/main/java/com/ModeratorElection/MainView.java

@@ -12,6 +12,7 @@ import com.vaadin.flow.component.notification.Notification;
 import com.vaadin.flow.component.notification.NotificationVariant;
 import com.vaadin.flow.component.orderedlayout.HorizontalLayout;
 import com.vaadin.flow.component.orderedlayout.VerticalLayout;
+import com.vaadin.flow.router.PreserveOnRefresh;
 import com.vaadin.flow.router.Route;
 import com.vaadin.flow.router.PageTitle;
 import org.springframework.beans.factory.annotation.Value;
@@ -23,6 +24,7 @@ import java.util.List;
 
 @Route("")
 @PageTitle("Moderatorenwahl")
+@PreserveOnRefresh
 @Configuration
 public class MainView extends VerticalLayout {