Chapter 11. Form component interceptors

11.1. Introduction

Form component interceptors provide a way to intercept and add extra functionality to input components on a form.

The application context specifies the list of interceptors to attach to controls constructed by the platform. This allows for a declarative model for specifying "additional" functionality to be added to various components.

Examples are interceptors to overlay validation error images and background color changes, provide popup menus in text fields, and autocompletion (as you type) for comboboxes.

11.2. Creating your own interceptor

To create your own FormComponentInterceptor, you have to provide both a FormComponentInterceptor and a FormComponentInterceptorFactory implementation. 

public interface FormComponentInterceptor {
    public void processLabel(String propertyName, JComponent label);

    public void processComponent(String propertyName, JComponent component);
}

11.3. Configuration

The configuration of the interceptors in the application context is done by defining the FormComponentInterceptorFactory in the formComponentInterceptorFactory method.

This is the standard configuration: 

@Bean
public FormComponentInterceptorFactory formComponentInterceptorFactory() {
    ChainedInterceptorFactory factory = new ChainedInterceptorFactory();
    List<FormComponentInterceptorFactory> factories = Lists.newArrayList();
    factories.add(new ColorValidationInterceptorFactory());
    factories.add(new OverlayValidationInterceptorFactory());
    factories.add(new ShowCaptionInStatusBarInterceptorFactory());
    factories.add(new ShowDescriptionInStatusBarInterceptorFactory());
    factory.setInterceptorFactories(factories);
    return factory;
}

11.4. Built-in interceptors

There are a number of built-in interceptors provided with the framework. We’ll quickly explain them.

11.4.1. Error overlay image

There are a number of built-in interceptors provided with the framework. We’ll quickly explain them.

--- IMAGE ---

This class has been specifically made to work with Valkyrie’s validation framework and will show the errors coming from that framework

To configure this interceptor, you need to use this interceptor factory: 

new OverlayValidationInterceptorFactory()

11.4.2. Error background color

Changes the background color of the form component when an invalid value is entered. The color of the background can be set through a property.

To configure this interceptor, you need to use this interceptor factory: 

new ColorValidationInterceptorFactory()
--- IMAGE ---

11.4.3. Text editing popup (undo, copy, paste, ...)

Adds more advanced text editing functionality to text components. It adds a popup menu with "undo/redo/cut/copy/paste/select all" items. It also adds the standard keyboard accelerators for these commands to the component.

--- IMAGE ---

To configure this interceptor, you need to use this interceptor factory: 

new TextComponentPopupInterceptorFactory()

11.4.4. Combobox auto completion

Adds auto completion to a combobox.

--- IMAGE ---

To configure this interceptor, you need to use this interceptor factory: 

new ComboBoxAutoCompletionInterceptorFactory()

11.4.5. Overlay image indicating dirty value

Shows an image in the top left corner of the component if the contents of the component has been changed by the user. The image also has a tooltip showing the original value. To the right of the image is a small revert button. Pushing this button restores the original value in the component

--- IMAGE ---

To configure this interceptor, you need to use this interceptor factory: 

new DirtyIndicatorInterceptorFactory()

11.4.6. Select all text on focus

Selects all the text in text fields and spinners when they receive focus.

--- IMAGE ---

To configure this interceptor, you need to use this interceptor factory: 

new SelectAllFormComponentInterceptorFactory()

11.4.7. Setting the caret to the beginning of the field

If the text is set in a text component, the caret position is set to the end of the text. This means the beginning of the text will not be visible if the text is too long to fit in the text component.

This FormComponentInterceptor "fixes" this behavior, and sets the caret to position 0.

To configure this interceptor, you need to use this interceptor factory: 

new TextCaretFormComponentInterceptorFactory()

11.4.8. Showing a tooltip

If a form property has a caption defined in the messages.properties file it will be used as the tooltip for the form component.

To configure this interceptor, you need to use this interceptor factory: 

new ToolTipInterceptorFactory()

11.4.9. Changing the rendering of a checkbox

Allows customization on how a CheckBox form property is rendered, for example whether the label needs to be shown.

To configure this interceptor, you need to use this interceptor factory:

new CheckBoxFormComponentInterceptorFactory()

11.4.10. Showing the caption of the currently focussed component in the statusbar

Shows the caption of the form component in the statusbar when the component is focused.

To configure this interceptor, you need to use this interceptor factory: 

new ShowCaptionInStatusBarInterceptorFactory()

11.4.11. Showing the description of the currently focussed component in the statusbar

Shows the description of the form component in the statusbar when the component is focused.

To configure this interceptor, you need to use this interceptor factory: 

new ShowDescriptionInStatusBarInterceptorFactory()
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