Binding Beans and Data in a Desktop Application

This guide is an introduction to the support in NetBeans IDE 6.0 for beans binding and data binding in Java desktop applications.

Software and Files Needed for the Tutorial

For this tutorial you need to have the following software installed on your computer:

Introduction: Beans Binding in NetBeans IDE 6.0

Until the release of the beans binding library, it was somewhat cumbersome to connect UI components to databases or to keep values of component properties in sync. For example, displaying data from a standard database in a JTable required the manual creation of utility classes to handle the connection between the database and the JTable. And keeping values of different bean properties in sync (such as the value of a JTextField with the rendering of a visual bean) required hand-coding of listeners and event handlers.

The beans binding library simplifies and standardizes all of this. You can merely write a few lines of code to establish which properties of which components need to be kept in sync, and the beans binding library handles the rest. In the NetBeans IDE, beans binding features are integrated in the GUI Builder, so you can quickly get the behavior of your application coded soon after you have established the visual design.

Binding Properties to Other Properties

At its most basic, beans binding is a way to connect bean properties without using event listening and handling code.

To illustrate the concept of beans binding and how the IDE supports it, we will do a simple example where a user can adjust a slider to change a numerical value in a text field.

Source and Target

Now that we have set up the example, we are ready to create the binding. However, first we need to determine which component will be the source of the binding and which will be the target. The binding source component is where a value for the property first originates.

When binding in the GUI Editor, you initiate a binding on the target and then you declare the source in the Bind dialog box.

In this case, since the JSlider comes with a default range of values, we will use it as the source.

Note: Bindings can be two-way (read/write), so that changes in the target are automatically reflected in the source. However, the direction of the initial binding is always from the source to the target. See the information on Update Mode in the Advanced Binding Configuration section.

To bind the slider to the text field:

Right-click the text field component and choose Bind > text to open the Bind dialog box.
From the Binding Source combo box, select jSlider1.
From the Binding Expression combo box, select value int as shown in the image below.
Click OK.

You have just bound the value bean property of the slider to the text value of the text field.

In the design area, the text field should show the value 50. This value reflects the fact that the slider is in the middle position and the default range of values for the slider is from 0 to 100.

You can now run the application and see the binding in action.

To run the project:

Choose Run > Run Main Project.
In the Run Project dialog box, click OK to accept numberslider.NumberSliderForm as the main class.

The applications should start in a separate window. Adjust the slider in the running application and watch the value change in the text field.

Image showing the running application with the slider moved and the
text value changed.

Advanced Binding Configuration

The example above shows a straightforward binding with some default behaviors. But sometimes you might want or need to configure your binding differently. If that is the case, you can use the Advanced tab of the Binding dialog box.

Note: To better understand the classes and methods mentioned above, you can access the beans binding Javadoc documentation directly from the IDE. Choose Help > Javadoc References > Beans Binding. In the browser window that opens, click the org.jdesktop.beansbinding link to access documentation for those classes.

Binding Data to Components

Once you have created a new Java form and added components to the form, you can generate code to bind those components to data. The IDE makes it easy to bind data to Swing JTable, JList, and JComboBox components.

Before binding a component to data from a database, you need to have done the following things:

Creating Entity Classes

To create entity classes to represent the database that is to be bound to the JTable:

In the Projects window, right-click your project and choose New > Other, select the Persistence category, and select the Entity Classes from Database template.
In the Database Tables page of the wizard, select the database connection.
Once the Available Tables column is populated, select the tables that you want to use in your application and click Add to move them to the Selected Tables column. Click Next.
In the Entity Classes page of the wizard, make sure the Generate Named Query Annotations for Persistent Fields dialog box is selected.
Make any customizations that you want to make to the names of the generated classes and their location.
Click Create Persistence Unit.
In the Create Persistence Unit dialog box, make sure of the following things:
- That the selected Persistence Library is TopLink.
- That the selected Table Generation Strategy is "None".
Click Finish.
You should see nodes for the entity classes in the Projects window.

Binding Components to the Beans That Represent the Data

To bind the data to a JTable component:

Right-click the component in the GUI Builder and choose Bind > elements.
Click Import Data to Form. From the Import Data to Form dialog box, select the database table to which you want to bind your components. Click OK.
From the Binding Source combo box, select the item that represents the result list of the entity class. For example, if the entity class is called, Customer.java, the list object would be generated as customerList.
Leave the Binding Expression value as null.
If there are any database columns that you want to appear in the JTable, select those columns in the Selected list and move them to the Available list.
Select the Advanced tab to further configure the binding. For example, you can specify a validator or converter, or you can specify behavior if the binding source is null or unreadable.
Click OK.

To bind the data to a JList component:

Right-click the component in the GUI Builder and choose Bind > elements.
Click Import Data to Form. From the Import Data to Form dialog box, select the database table to which you want to bind your components. Click OK.
From the Binding Source combo box, select the item that represents the result list of the entity class. For example, if the entity class is called, Customer.java, the list object would be generated as customerList.
Leave the Binding Expression value as null.
In the Display Expression drop-down list, select the property that represents the database column that contains the values that you want to display in the list.
Select the Advanced tab to further configure the binding.
Click OK.

Note: You can also use the New Java Desktop Application wizard to quickly create a whole working application that has CRUD (create, read, update, and delete) features. However, it is better to generate all the entity classes in advance to ensure that all relations among the entities are correctly covered by the generated classes.

Special Binding Properties

Where necessary, the beans binding library provides special synthetic properties for some Swing components that are missing from the components themselves. These properties represent things, such as a table's selected row, that are useful to bind to other properties.

Below is a list of the synthetic properties added by the beans binding libraries:

Component	Property	Description
AbstractButton	selected	The selected state of a button.
JComboBox	selectedItem	The selected item of a JComboBox.
JSlider	value	The value of a JSlider; notifies of all changes.
JSlider	value_IGNORE_ADJUSTING	Same as "value" but does not notify of change while the slider is adjusting its value.
JList	selectedElement	The selected element of a JList; notifies of all changes. If there is a JListBinding with the JList as the target, the selected element is reported as an element from the binding's source list. Otherwise, the selected element is reported as an object from the list's model. If nothing is selected, the property evaluates to `null`.
	selectedElements	A list containing the selected elements of a JList; notifies of all changes. If there is a JListBinding with the JList as the target, the selected elements are reported as elements from the binding's source list. Otherwise, the selected elements are reported as objects from the list's model. If nothing is selected, the property evaluates to an empty list.
	selectedElement_IGNORE_ADJUSTING	Same as "selectedElement" but does not notify of change while the list selection is being updated.
	selectedElements_IGNORE_ADJUSTING	Same as "selectedElements" but does not notify of change while the list selection is being updated.
JTable	selectedElement	The selected element of a JTable; notifies of all changes. If there is a JTableBinding with the JTable as the target, the selected element is reported as an element from the binding's source list. Otherwise, the selected element is reported as a map where the keys are composed of the string "column" plus the column index and the values are the model values for that column. Example: {column0=column0value, column1=column1value, ...} If nothing is selected, the property evaluates to `null`.
	selectedElements	A list containing the selected elements of a JTable; notifies of all changes. If there is a JTableBinding with the JTable as the target, the selected elements are reported as elements from the binding's source list. Otherwise, each selected element is reported as a map where the keys are composed of the string "column" plus the column index and the values are the model values for that column. Example: {column0=column0value, column1=column1value, ...} If nothing is selected, the property evaluates to an empty list.
	selectedElement_IGNORE_ADJUSTING	Same as "selectedElement" but does notify of change while the table selection is being updated.
	selectedElements_IGNORE_ADJUSTING	Same as "selectedElements" but does not notify of change while the table selection is being updated.
JTextComponent (including its sub-classes JTextField, JTextArea, and JEditorPane)	text	The text property of a JTextComponent; notifies of all changes (including typing).
	text_ON_FOCUS_LOST	The text property of a JTextComponent; notifies of change only when focus is lost on the component.
	text_ON_ACTION_OR_FOCUS_LOST	The text property of a JTextComponent; notifies of change only when the component notifies of actionPerformed or when focus is lost on the component.