I have one fxml file controlled by one controller. I want to separate the controller into multiple parts as if placed in one controller makes a long code. Unfortunately, fx:controller can only be placed in the root. Are there any suggestions for me how to separate the controller?
I recommend to create custom controls - use several smaller FXML files rather than one big FXML file.
Here is the tutorial:
http://docs.oracle.com/javafx/2/fxml_get_started/custom_control.htm
During the loading of your FXML markup, there is only the provision to have one controller specified for your scene graph. You are able to load other FXML markup files and nest controllers, but I don't think that's what you're asking.
To my mind, it doesn't matter anyway.
You can write any number of classes in any number of files and have them interact with your controller class just like any Java class can interact with any other Java class.
I really can't think of any particularly good reason why it would be useful to specify multiple controllers for a scene graph at load time.
You can add an fxml file as a node into another fxml , both with diferent controllers with include option in scene builder
来源：https://stackoverflow.com/questions/16879826/multiple-controller-for-one-fxml-file