Javafx error exception in Application start method no controller specified
The error says it, the FXML is missing the fx:controller
declaration. Add the controller declaration to BorderPane
declaration as shown :
...
<BorderPane maxHeight="1.7976931348623157E308"
maxWidth="1.7976931348623157E308" prefHeight="400.0"
prefWidth="600.0" xmlns="http://javafx.com/javafx/8"
xmlns:fx="http://javafx.com/fxml/1"
fx:controller="Weert.Controller">
...
To know how to set controller class via SceneBuilder, you can have a look at this question.