Hey there, let's work through this FileChooser issue you're hitting. From your description, the exception fires when you call showOpenDialog(...) inside your EmailSenderController.addHtml() method—when trying to load an HTML file into your HTML editor. You mentioned you didn't manually initialize your @FXML-injected controls like similar posts suggested, so let's break down actionable fixes to get this working:

1. Make sure you're calling FileChooser on the JavaFX Application Thread #

JavaFX UI components (including FileChooser) must be accessed from the main application thread. If your addHtml() method is triggered from a background thread (like a network task, timer, or external callback), that'll throw an exception immediately.

Fix this by wrapping your FileChooser logic in Platform.runLater():

@FXML
private void addHtml() {
    Platform.runLater(() -> {
        FileChooser fileChooser = new FileChooser();
        // Add file filters if needed
        fileChooser.getExtensionFilters().add(new FileChooser.ExtensionFilter("HTML Files", "*.html", "*.htm"));
        
        // Get the stage from your HTML editor's scene (instead of passing null)
        Stage stage = (Stage) yourHtmlEditor.getScene().getWindow();
        File selectedFile = fileChooser.showOpenDialog(stage);
        
        if (selectedFile != null) {
            // Load the file content into your HTML editor here
        }
    });
}

2. Validate the Stage reference passed to showOpenDialog #

Passing null as the stage argument can cause unexpected behavior on certain OSes (especially Linux with specific window managers). Instead, grab the stage from your existing UI components—like your HTML editor's parent window—using the code above. This gives FileChooser a proper context to open in.

3. Double-check @FXML injection (even without manual initialization) #

Even if you're not manually initializing controls, ensure your FXML file's fx:id values match exactly with your controller's @FXML fields. A mismatch here could lead to a NullPointerException when you try to interact with the HTML editor, which might cascade into the FileChooser exception.

For example:

• In your FXML: <HTMLEditor fx:id="emailHtmlEditor" />
• In your controller: @FXML private HTMLEditor emailHtmlEditor;

4. Verify module dependencies (for Java 9+) #

If you're using modular Java, your module-info.java needs to include the required JavaFX modules to access FileChooser and HTMLEditor:

module your.app.module {
    requires javafx.controls;
    requires javafx.web; // HTMLEditor lives in this module
    opens com.yourpackage.controllers to javafx.fxml; // Let FXML access your controller
}

5. Catch and log the full exception stack trace #

Right now you know there's an exception, but the exact error message will tell you the root cause. Wrap your FileChooser code in a try-catch block to capture the stack trace:

@FXML
private void addHtml() {
    Platform.runLater(() -> {
        try {
            FileChooser fileChooser = new FileChooser();
            Stage stage = (Stage) yourHtmlEditor.getScene().getWindow();
            File selectedFile = fileChooser.showOpenDialog(stage);
            
            if (selectedFile != null) {
                // Load content into editor
            }
        } catch (Exception e) {
            e.printStackTrace(); // Or use a logger for cleaner output
        }
    });
}

The stack trace will point to specifics like a thread violation, missing permissions, or invalid UI component state.

内容的提问来源于stack exchange，提问作者DJava