JavaFX 2.0 FXML resource loading error

For me is better to have a schema that you can map directly to code (easy to automate), mainly because code is what is going to be at both ends.

GET  /orders          <---> orders 
POST /orders          <---> orders.push(data)
GET  /orders/1        <---> orders[1]
PUT  /orders/1        <---> orders[1] = data
GET  /orders/1/lines  <---> orders[1].lines
POST /orders/1/lines  <---> orders[1].lines.push(data) 

Update: For an up-to-date tutorial, please, consult the official documentation. There was a lot of new stuff that was added in 2.2. Also, the Introduction to FXML covers pretty much everything you need to know about FXML. Finally, Hendrik Ebbers made an extremely helpful blog post about custom UI controls.

After a few days of looking around the API and reading through some docs (Intro to FXML, Getting started with FXML Property binding, Future of FXML) I've come up with a fairly sensible solution. The least straight-forward piece of information I learned from this little experiment was that the instance of a controller (declared with fx:controller in FXML) is held by the FXMLLoader that loaded the FXML file... Worst of all, this important fact is only mentioned in one place in all the docs I saw:

a controller is generally only visible to the FXML loader that creates it

So, remember, in order to programmatically (from Java code) obtain a reference to the instance of a controller that was declared in FXML with fx:controller use FXMLLoader.getController() (refer to the implementation of the ChoiceCell class below for a complete example).

Another thing to note is that Property.bindBiderctional() will set the value of the calling property to the value of the property passed in as the argument. Given two boolean properties target (originally set to false) and source (initially set to true) calling target.bindBidirectional(source) will set the value of target to true. Obviously, any subsequent changes to either property will change the other property's value (target.set(false) will cause the value of source to be set to false):

BooleanProperty target = new SimpleBooleanProperty();//value is false
BooleanProperty source = new SimpleBooleanProperty(true);//value is true
target.bindBidirectional(source);//target.get() will now return true
target.set(false);//both values are now false
source.set(true);//both values are now true

Anyway, here is the complete code that demonstrates how FXML and Java can work together (as well as a few other useful things)

Package structure:

com.example.javafx.choice
  ChoiceCell.java
  ChoiceController.java
  ChoiceModel.java
  ChoiceView.fxml
com.example.javafx.mvc
  FxmlMvcPatternDemo.java
  MainController.java
  MainView.fxml
  MainView.properties

FxmlMvcPatternDemo.java

package com.example.javafx.mvc;

import java.util.ResourceBundle;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class FxmlMvcPatternDemo extends Application
{
    public static void main(String[] args) throws ClassNotFoundException
    {
        Application.launch(FxmlMvcPatternDemo.class, args);
    }

    @Override
    public void start(Stage stage) throws Exception
    {
        Parent root = FXMLLoader.load
        (
            FxmlMvcPatternDemo.class.getResource("MainView.fxml"),
            ResourceBundle.getBundle(FxmlMvcPatternDemo.class.getPackage().getName()+".MainView")/*properties file*/
        );

        stage.setScene(new Scene(root));
        stage.show();
    }
}

MainView.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<VBox
    xmlns:fx="http://javafx.com/fxml"
    fx:controller="com.example.javafx.mvc.MainController"

    prefWidth="300"
    prefHeight="400"
    fillWidth="false"
>
    <children>
        <Label text="%title" />
        <ListView fx:id="choicesView" />
        <Button text="Force Change" onAction="#handleForceChange" />
    </children>
</VBox>

MainView.properties

title=JavaFX 2.0 FXML MVC demo

MainController.java

package com.example.javafx.mvc;

import com.example.javafx.choice.ChoiceCell;
import com.example.javafx.choice.ChoiceModel;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.collections.FXCollections;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.util.Callback;

public class MainController implements Initializable
{
    @FXML
    private ListView<ChoiceModel> choicesView;

    @Override
    public void initialize(URL url, ResourceBundle rb)
    {
        choicesView.setCellFactory(new Callback<ListView<ChoiceModel>, ListCell<ChoiceModel>>()
        {
            public ListCell<ChoiceModel> call(ListView<ChoiceModel> p)
            {
                return new ChoiceCell();
            }
        });
        choicesView.setItems(FXCollections.observableArrayList
        (
            new ChoiceModel("Tiger", true),
            new ChoiceModel("Shark", false),
            new ChoiceModel("Bear", false),
            new ChoiceModel("Wolf", true)
        ));
    }

    @FXML
    private void handleForceChange(ActionEvent event)
    {
        if(choicesView != null && choicesView.getItems().size() > 0)
        {
            boolean isSelected = choicesView.getItems().get(0).isSelected();
            choicesView.getItems().get(0).setSelected(!isSelected);
        }
    }
}

ChoiceView.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<HBox
    xmlns:fx="http://javafx.com/fxml"

    fx:controller="com.example.javafx.choice.ChoiceController"
>
    <children>
        <CheckBox fx:id="isSelectedView" />
        <Label fx:id="labelView" />
    </children>
</HBox>

ChoiceController.java

package com.example.javafx.choice;

import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.CheckBox;
import javafx.scene.control.Label;

public class ChoiceController
{
    private final ChangeListener<String> LABEL_CHANGE_LISTENER = new ChangeListener<String>()
    {
        public void changed(ObservableValue<? extends String> property, String oldValue, String newValue)
        {
            updateLabelView(newValue);
        }
    };

    private final ChangeListener<Boolean> IS_SELECTED_CHANGE_LISTENER = new ChangeListener<Boolean>()
    {
        public void changed(ObservableValue<? extends Boolean> property, Boolean oldValue, Boolean newValue)
        {
            updateIsSelectedView(newValue);
        }
    };

    @FXML
    private Label labelView;

    @FXML
    private CheckBox isSelectedView;

    private ChoiceModel model;

    public ChoiceModel getModel()
    {
        return model;
    }

    public void setModel(ChoiceModel model)
    {
        if(this.model != null)
            removeModelListeners();
        this.model = model;
        setupModelListeners();
        updateView();
    }

    private void removeModelListeners()
    {
        model.labelProperty().removeListener(LABEL_CHANGE_LISTENER);
        model.isSelectedProperty().removeListener(IS_SELECTED_CHANGE_LISTENER);
        isSelectedView.selectedProperty().unbindBidirectional(model.isSelectedProperty())
    }

    private void setupModelListeners()
    {
        model.labelProperty().addListener(LABEL_CHANGE_LISTENER);
        model.isSelectedProperty().addListener(IS_SELECTED_CHANGE_LISTENER);
        isSelectedView.selectedProperty().bindBidirectional(model.isSelectedProperty());
    }

    private void updateView()
    {
        updateLabelView();
        updateIsSelectedView();
    }

    private void updateLabelView(){ updateLabelView(model.getLabel()); }
    private void updateLabelView(String newValue)
    {
        labelView.setText(newValue);
    }

    private void updateIsSelectedView(){ updateIsSelectedView(model.isSelected()); }
    private void updateIsSelectedView(boolean newValue)
    {
        isSelectedView.setSelected(newValue);
    }
}

ChoiceModel.java

package com.example.javafx.choice;

import javafx.beans.property.BooleanProperty;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

public class ChoiceModel
{
    private final StringProperty label;
    private final BooleanProperty isSelected;

    public ChoiceModel()
    {
        this(null, false);
    }

    public ChoiceModel(String label)
    {
        this(label, false);
    }

    public ChoiceModel(String label, boolean isSelected)
    {
        this.label = new SimpleStringProperty(label);
        this.isSelected = new SimpleBooleanProperty(isSelected);
    }

    public String getLabel(){ return label.get(); }
    public void setLabel(String label){ this.label.set(label); }
    public StringProperty labelProperty(){ return label; }

    public boolean isSelected(){ return isSelected.get(); }
    public void setSelected(boolean isSelected){ this.isSelected.set(isSelected); }
    public BooleanProperty isSelectedProperty(){ return isSelected; }
}

ChoiceCell.java

package com.example.javafx.choice;

import java.io.IOException;
import java.net.URL;
import javafx.fxml.FXMLLoader;
import javafx.fxml.JavaFXBuilderFactory;
import javafx.scene.Node;
import javafx.scene.control.ListCell;

public class ChoiceCell extends ListCell<ChoiceModel>
{
    @Override
    protected void updateItem(ChoiceModel model, boolean bln)
    {
        super.updateItem(model, bln);

        if(model != null)
        {
            URL location = ChoiceController.class.getResource("ChoiceView.fxml");

            FXMLLoader fxmlLoader = new FXMLLoader();
            fxmlLoader.setLocation(location);
            fxmlLoader.setBuilderFactory(new JavaFXBuilderFactory());

            try
            {
                Node root = (Node)fxmlLoader.load(location.openStream());
                ChoiceController controller = (ChoiceController)fxmlLoader.getController();
                controller.setModel(model);
                setGraphic(root);
            }
            catch(IOException ioe)
            {
                throw new IllegalStateException(ioe);
            }
        }
    }
}