Breaking JavaFX when Tab character is pasted into TextField

Question

The JavaFX Application Thread throws a StringIndexOutOfBoundsException if the user pastes a tab character into a TextField. How can I smartly prevent a user from breaking my application in this way?

Here's a minimal example that demonstrates the behavior.

//Defined in Main.java
public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {
            AnchorPane root = (AnchorPane) FXMLLoader
                    .load(getClass().getResource("MainView.fxml"));
            primaryStage.setScene(new Scene(root));
            primaryStage.show();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

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

Defined in MainView.fxml:

<AnchorPane xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1">
    <children>
        <TextField fx:id="tf" />
    </children>
</AnchorPane>

Procedure:

1. Copy a tab character (\t) to the clipboard
2. Type something into the TextField
3. Highlight the text in the TextField
4. Paste the contents of the clipboard to replace the highlighted text

The exception occurs whether the user uses the keyboard shortcut (Ctrl+V in Windows) or the context menu. I certainly could add a try-catch block to every TextField, but that would clutter up the code, and how do I know that this exception is only thrown in this one situation?

Note: This is issue does not appear to affect TextArea

Full text of the exception:

Exception in thread "JavaFX Application Thread" java.lang.StringIndexOutOfBoundsException: String index out of range: 1
at java.lang.AbstractStringBuilder.substring(Unknown Source)
at java.lang.StringBuilder.substring(Unknown Source)
at javafx.scene.control.TextField$TextFieldContent.get(Unknown Source)
at javafx.scene.control.TextInputControl.getText(Unknown Source)
at javafx.scene.control.TextInputControl.updateContent(Unknown Source)
at javafx.scene.control.TextInputControl.replaceText(Unknown Source)
at javafx.scene.control.TextInputControl.replaceText(Unknown Source)
at javafx.scene.control.TextInputControl.replaceSelection(Unknown Source)
at javafx.scene.control.TextInputControl.paste(Unknown Source)
at com.sun.javafx.scene.control.behavior.TextInputControlBehavior.paste(Unknown Source)
at com.sun.javafx.scene.control.behavior.TextInputControlBehavior.callAction(Unknown Source)
at com.sun.javafx.scene.control.behavior.BehaviorBase.callActionForEvent(Unknown Source)
at com.sun.javafx.scene.control.behavior.TextInputControlBehavior.callActionForEvent(Unknown Source)
at com.sun.javafx.scene.control.behavior.BehaviorBase.lambda$new$74(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at javafx.event.Event.fireEvent(Unknown Source)
at javafx.scene.Scene$KeyHandler.process(Unknown Source)
at javafx.scene.Scene$KeyHandler.access$1800(Unknown Source)
at javafx.scene.Scene.impl_processKeyEvent(Unknown Source)
at javafx.scene.Scene$ScenePeerListener.keyEvent(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleKeyEvent$353(Unknown Source)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(Unknown Source)
at com.sun.glass.ui.View.handleKeyEvent(Unknown Source)
at com.sun.glass.ui.View.notifyKey(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(Unknown Source)
at java.lang.Thread.run(Unknown Source)

Answer 1

Well that's ugly. You should report this as a bug.

You can workaround this with a TextFormatter which filters out tab (and newline) characters. You might want to replace the tab character with, e.g. four spaces.

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.control.TextFormatter;
import javafx.scene.control.TextFormatter.Change;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class TextFieldBug extends Application {

    @Override
    public void start(Stage primaryStage) {
        TextField tf = new TextField();
        tf.setTextFormatter(new TextFormatter<String>((Change c) -> {
            String text = c.getText();
            int oldAnchor = c.getAnchor();
            int oldCaretPos = c.getCaretPosition() ;
            int initialLength = text.length();
            text = text.replaceAll("\t", "    ");
            text = text.replaceAll("\n", "");
            c.setText(text);
            c.setAnchor(oldAnchor + text.length() - initialLength);
            c.setCaretPosition(oldCaretPos + text.length() - initialLength);
            return c ;
        }));
        primaryStage.setScene(new Scene(new StackPane(tf), 350, 120));
        primaryStage.show();
    }

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