Shortening method based on an argument name
Without seeing the greater context in which this code appears such as how the components are constructed, and not having kept up with Spring since 1999, I can only address the immediate code. The above could be converted to use two maps: one for the text fields and another for the currentScale strings.

In the code that builds the components, create the two maps and store them in instance fields of the same class.

private final Map&lt;Object, JTextField&gt; textFieldsByRadioButton = new IdentityHashMap&lt;&gt;();
private final Map&lt;Object, String&gt; scalesByRadioButton = new IdentityHashMap&lt;&gt;();

private void buildComponents() {
    ...
    addRadioButtonSpinnerMapping(rRadioButton, rSpinner, "r");
    addRadioButtonSpinnerMapping(gRadioButton, gSpinner, "g");
    addRadioButtonSpinnerMapping(bRadioButton, bSpinner, "b");
}

private void addRadioButtonSpinnerMapping(JRadioButton button, JSpinner spinner, String scale) {
    textFieldsByRadioButton.put(button, ((DefaultEditor) spinner.getEditor()).getTextField());
    scalesByRadioButton.put(button, scale);
}

public void itemStateChanged(ItemEvent ie) {
    Object source = ie.getSource();
    JTextField textField = textFieldsByRadioButton.get(source);
    if (textField != null) {
        currentScale = scalesByRadioButton.get(source);
        textField.requestFocus();
    }
    ...
}


While it requires slightly more code, it only takes one line to add another spinner.