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Our BusinessObjects have a list of static information called Attributes, which have the constructor:
Code:

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Attribute.java:
Attribute(Class parentClass, Class modelClass, String dbColumn, int maxLength, Object initialValue, boolean allowNull, String name, int length, Class theWidgetClass)  

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Where parentClass is the specific BusinessObject subclass (Customer), the modelClass is the underlying datatype (BigDecimal, String); maxLength, allowNull, dbColumn refer to the static information used to read data out of the database (we use Oracle databases almost exclusively, so scattering some SQL code in our framework seemed like a reasonable compromise); name, length, and theWidgetClass refer to how the Attribute is displayed.

Dynamic information is abstracted as FieldModels.
Code:

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FieldModel.java:
FieldModel(Attribute attr)

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Further, created an abstraction for our GUI elements called FieldComponent and extended some Swing Components (and custom created a few more), so that user-entered data is written directly to the component's FieldModel.
Code:

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FieldComponent.java:
FieldComponent.setFieldModel(FieldModel model)

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The principle is similar to a JTextComponent writing its data directly to a Document and then reading the Document's information. FieldComponents also have a sync() method that is called in response to user events (FocusEvents, MouseEvents,etc) to keep the FieldModel synchronized with the FieldComponent.

The BusinessObject's method for painting its Form (a subclass of JPanel) is quite simple:

Code:

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Customer.java:
public static Form getForm() {
    Form entryForm= new Form();
    entryForm.add(attribute1.labelComponent());
    entryForm.add(attribute1.fieldComponent());
    //...
    return form;
}

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This creates a blank form. We ask the Customer to attach itself to this Form, populating the the FieldModels with the appropriate data:

Code:

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Customer.java:
// NOTE: CustomNumericField is a subclass of JTextField (and implements FieldComponent) accepting only numeric characters
public static final Attribute attribute1 =
        new Attribute(Customer.class, java.math.BigDecimal.class, "COLUMN_1", 8, new java.math.BigDecimal(0.0), false, "Column 1", 15, CustomNumericField.class);
	
// FieldModelList is a Vector of FieldModels.
private FieldModelList fields = new FieldModelList();
private FieldModel fieldModel1 = fields.addFieldModel( attribute1.createFieldModel(), this );
//...
public void attach(Form form, boolean editable) {
    Enumeration enum = fields.fields();
    while ( enum.hasMoreElements() )
	form.attach( (FieldModel) enum.nextElement(), editable );
    }
}

Form.java:
public void attach( FieldModel fm, boolean editable ){
    //get the component from a Hashtable, indexed by name
    Component comp = componentForName( fm.attribute().name() );
    if (comp != null && comp instanceof FieldComponent){
        fm.attach ((FieldComponent)comp, editable);
    }
}

FieldModel.java:
public void attach( FieldComponent fui, boolean editable ) {
    fui.setFieldModel( this );
    fui.setUIEditable( editable );
    fieldComponent = fui;
}

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When the user wants to edit the Customer information, the CustomerEntryForm calls opens a transaction (tx), and passes the call to the CustomerManager:

Code:

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CustomerManager.java:
// throws our custom BusinessObject exceptions
public static Customer editableCustomer(Customer customer, TX tx ) throws BOException.CannotGetLock, BOException.BODoesNotExist {
    if ( tx == null || customer == null)
        throw new NullPointerException("Tx and Customer required" );
    try {
    	// BOFactory is a singleton which acts as a Facade to the Oracle database, hiding JDBC calls 
	return (Customer) BOFactory.getFactory().findLockedBO( Customer.class, customer.getBOPK(), null, tx );
    } catch (RemoteException re) {
        throw new RuntimeException("RemoteException Occurred: " + re);
    }
}

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editableCustomer is then attached to the Form. When the user wants to save this information, the CustomerManager is invoked again, passing the same transaction used to created the editableCustomer:

Code:

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CustomerManager.java:
public static boolean saveCustomer( Customer customer, TX tx ) {
    if ( tx == null || customer == null)
        throw new NullPointerException("Tx and Customer required");
    IBOFactory bof=null;
    try {
        BOPK key = BOFactory.getFactory().save( tx, customer );
	customer.setBOPK( key ); // set key on local VM to that which was saved
	return true;
    } catch(Exception e){
        System.out.println(e.getMessage());
        e.printStackTrace();
        return false;
    }
}

BOFactory.java:
public BOPK save( TX tx, BusinessObject bo ) throws RemoteException {
    if (!isTXValid( tx )){
	throw new BOException.General( "Invalid transaction" );
    }
    try {
        bo.save( tx );
	return bo.getBOPK();
    } catch (SQLException e){
         rollback( tx );
         throw new BOException.SQLException( "SQL Exception saving bo to database tx= " + tx + " bo= " + bo, e );
    } catch ( Throwable e ) {
         e.printStackTrace();
	throw new BOException.General( "Exception in BOFactory.save(tx,bo)", e );
    }
}

Customer.java:
// combining BusinessObject.save and Customer.save for simplicity (shows update only):
public void save(TX tx) {
    IBOFactory bof = BOFactory.getFactory();
    ResultSet rset = null;
    try {
        String where = pkname + " = "+ bo.getBOPK();	
	rset = bof.runUpdatableQuery( tx, "Select " + SQLColumns+" from " + SQLTableName + " where " + where );
        rset.next();
	save( rset );
	rset.updateRow();
    } catch (RemoteException re) {
	throw new BOException.General("RemoteException: " + re);
    } catch (SQLException e) {
	throw e;
    } finally {
	if (rset != null ) {
	    rset.getStatement().close();
	    rset.close();
	}
    }
} 

public void save( ResultSet rset ) throws SQLException {
    rset.updateInt( pkname, key.toInt() );
    save( fields, rset );
}

public static void save( FieldModelList fields, ResultSet rset ) throws SQLException {
    Enumeration e = fields.fields();
    while (e.hasMoreElements()) {
        FieldModel field = (FieldModel) e.nextElement();
	field.save( rset );
    }
}

FieldModel.java:
public void save( ResultSet rset ) throws SQLException {
    //resets the attribute for this FieldModel
    attribute();
    // get the modelClass, dbColumn name from the Attribute class
    if ( attribute == null || attribute.modelClass() == null )
        return;
    String dbColumn = attribute.dbColumn();
    if ( dbColumn == null ||
	dbColumn.equals(""))
    return;
    Class modelClass = attribute.modelClass();
    try {
    	// write data from FieldModel to ResultSet
	if (getValue()==null)
	    rset.updateObject( dbColumn, null );
	else if (java.util.Date.class.isAssignableFrom( modelClass ))
	    rset.updateObject( dbColumn, new java.sql.Date(((java.util.Date)getValue()).getTime() ));
	else if ( Boolean.class.isAssignableFrom( modelClass ) )
	    rset.updateBoolean( dbColumn, ((Boolean) getValue()).booleanValue() );
	else if ( Integer.class.isAssignableFrom( modelClass ) )
	    rset.updateInt( dbColumn, ((Integer) getValue()).intValue() );
	else
 	    rset.updateObject( dbColumn, getValue() );
    } catch( SQLException e ) {
	e.setNextException( new SQLException("Error occurred in FieldModel.save() storing data to column= "+dbColumn) );
	throw e;
    }
}

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All the code for user and database interactions are actually hidden in the FieldModel, Attribute, and FieldComponent classes. BusinessObject contains the basic behaviour for creating, reading, updating, saving and deleting BusinessObjects. All that the developer has to do is create the code specific for Customer's behaviour and its appearance on the Form. Displaying the Customer on a JTable is similar to displaying it on a Form. We use a BOTableModel (subclassing AbstractTableModel) to gather information about the Customer's known Attributes, necessary to create the JTable's structure (number of columns, headers, cell renderers, widths), and display the data from the FieldModel (I'll leave this as a Simple Exercise For The Student).

bsj

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