JavaFX open new window issue with fxml

Question

I'm developing a password manager program. When opening a new window in this program it throws an exception on the addEntry() mouse click event. I have a Main class that opens the main window (with sample.fxml ) and a Controller class that manages to open the new window (with addNewEntryDialog.fxml ). Here's my code:

Main.java

package sample;

import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Modality;
import javafx.stage.Stage;

import java.io.IOException;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("/sample.fxml"));
        primaryStage.setTitle("Password Manager");
        primaryStage.setScene(new Scene(root, 800, 600));
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

Controller.java

package sample;

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.control.cell.PropertyValueFactory;
import javafx.stage.Stage;
import javafx.stage.StageStyle;

import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.ResourceBundle;

public class Controller implements Initializable {
    public ObservableList<Data> data;
    public TableView dbTable;
    public TableColumn siteColumn, usernameColumn, passwordColumn;

    public ToggleButton showPasswordToggle;


    @Override
    public void initialize(URL location, ResourceBundle resources) {
        fillTable();
    }

    public void fillTable(){
        data = FXCollections.observableArrayList();
        String query = "SELECT * FROM accounts";

        try {
            Connection connection = connectToDatabase();
            ResultSet resultSet = connection.createStatement().executeQuery(query);

            while (resultSet.next()) {
                data.add(new Data(resultSet.getString(1), resultSet.getString(2), resultSet.getString(3)));
            }

            siteColumn.setCellValueFactory(new PropertyValueFactory("site"));
            usernameColumn.setCellValueFactory(new PropertyValueFactory("username"));
            passwordColumn.setCellValueFactory(new PropertyValueFactory("password"));

            dbTable.setItems(data);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    @FXML
    public void addEntry() throws IOException {
        Stage stage = new Stage();
        Parent root = FXMLLoader.load(getClass().getResource("/addEntryDialog.fxml"));
        stage.setTitle("Add new entry");
        stage.setScene(new Scene(root, 800, 600));
        stage.show();
    }

addEntryDialog.fxml

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

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

<Pane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="200.0" prefWidth="400.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <GridPane layoutX="28.0" layoutY="21.0" prefHeight="123.0" prefWidth="317.0">
         <columnConstraints>
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
         </columnConstraints>
         <rowConstraints>
            <RowConstraints minHeight="10.0" vgrow="SOMETIMES" />
            <RowConstraints minHeight="10.0" vgrow="SOMETIMES" />
            <RowConstraints minHeight="10.0" vgrow="SOMETIMES" />
         </rowConstraints>
         <children>
            <Label layoutX="33.0" layoutY="26.0" text="Site:" />
            <Label layoutX="28.0" layoutY="78.0" text="Username:" GridPane.rowIndex="1" />
            <Label layoutX="44.0" layoutY="135.0" text="Password:" GridPane.rowIndex="2" />
            <TextField fx:id="siteField" layoutX="150.0" layoutY="21.0" GridPane.columnIndex="1" />
            <TextField fx:id="usernameField" layoutX="150.0" layoutY="73.0" GridPane.columnIndex="1" GridPane.rowIndex="1" />
            <PasswordField fx:id="passwordField" layoutX="150.0" layoutY="123.0" GridPane.columnIndex="1" GridPane.rowIndex="2" />
         </children>
      </GridPane>
      <Button layoutX="327.0" layoutY="163.0" mnemonicParsing="false" text="OK" />
      <Button layoutX="246.0" layoutY="163.0" mnemonicParsing="false" text="Cancel" />
   </children>
</Pane>

sample.fxml

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

<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>

<Pane prefHeight="600.0" prefWidth="800.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <TableView fx:id="dbTable" layoutX="4.0" layoutY="85.0" prefHeight="505.0" prefWidth="790.0">
        <columns>
          <TableColumn fx:id="siteColumn" prefWidth="263.0" text="Site" />
          <TableColumn fx:id="usernameColumn" prefWidth="263.0" text="Username" />
          <TableColumn fx:id="passwordColumn" prefWidth="263.0" text="Password" />
        </columns>
      </TableView>
      <GridPane layoutX="14.0" layoutY="27.0" prefHeight="25.0" prefWidth="263.0">
         <columnConstraints>
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
         </columnConstraints>
         <rowConstraints>
            <RowConstraints minHeight="10.0" vgrow="SOMETIMES" />
         </rowConstraints>
         <children>
            <Button fx:id="addNewEntry" layoutX="14.0" layoutY="14.0" mnemonicParsing="false" onMouseClicked="#addEntry" text="Add.." GridPane.columnIndex="0" />
            <Button fx:id="removeEntry" layoutX="83.0" layoutY="14.0" mnemonicParsing="false" text="Remove.." GridPane.columnIndex="1" />
            <Button fx:id="editEntry" layoutX="178.0" layoutY="14.0" mnemonicParsing="false" text="Edit.." GridPane.columnIndex="2" />
         </children>
      </GridPane>
      <ToggleButton fx:id="showPasswordToggle" layoutX="671.0" layoutY="27.0" mnemonicParsing="false" text="Show Password" />
   </children>
</Pane>

STACK TRACE

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3470)
    at javafx.scene.Scene$ClickGenerator.access$8100(Scene.java:3398)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3766)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:388)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication.lambda$null$49(GtkApplication.java:139)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 31 more
Caused by: javafx.fxml.LoadException: 
/home/umberto/passwordManager/out/production/passwordManager/addEntryDialog.fxml

    at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3214)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3175)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3148)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3124)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3104)
    at javafx.fxml.FXMLLoader.load(FXMLLoader.java:3097)
    at sample.Controller.addEntry(Controller.java:58)
    ... 41 more
Caused by: java.lang.NullPointerException
    at sample.Controller.loadTableData(Controller.java:45)
    at sample.Controller.initialize(Controller.java:30)
    at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
    ... 49 more

Answer 1

Look at your addEntryDialog.fxml file. There is definition of this view's controller:

<Pane ... fx:controller="sample.Controller>

JavaFX loads the view, looks for the controller and creates it. (At this moment another sample.Controller object is instantiated). After creating it sees that this controller implements Initializable interface, so it executes initialize method which in turn calls fillTable method and finally the statement siteColumn.setCellValueFactory(..) is reached. The problem is that there's no siteColumn for addEntryDialog.fxml view - it has not been binded since there's no element on view with that id.

Solution is to create proper controller for addEntryView.fxml and call it in xml fx:controller attribute.