The Java EE 5 Tutorial

Setting the Component Property Values

To pass the value of the tag attributes to MapComponent, the tag handler implements the setProperties method. The way setProperties passes the attribute values to the component class depends on whether the values are value expressions or method expressions.

Setting Value Expressions on Component Properties

When the attribute value is a value expression, setProperties first checks if it is not a literal expression. If the expression is not a literal, setProperties stores the expression into a collection, from which the component class can retrieve it and resolve it at the appropriate time. If the expression is a literal, setProperties performs any required type conversion and then does one of the following:

The following piece of the MapTag handler’s setProperties method sets the renderer-dependent property, styleClass, and the renderer-independent property, immediate:

if (styleClass != null) {
    if (!styleClass.isLiteralText()) {
        map.setValueExpression("styleClass", styleClass);
    } else {
if (immediate != null) {
    if (!immediate.isLiteralText()) {
        map.setValueExpression("immediate", immediate);
    } else {

Setting Method Expressions on Component Properties

The process of setting the properties that accept method expressions is done differently depending on the purpose of the method. The actionListener attribute uses a method expression to reference a method that handles action events. The action attribute uses a method expression to either specify a logical outcome or to reference a method that returns a logical outcome, which is used for navigation purposes.

To handle the method expression referenced by actionListener, the setProperties method must wrap the expression in a special action listener object called MethodExpressionActionListener. This listener executes the method referenced by the expression when it receives the action event. The setProperties method then adds this MethodExpressionActionListener object to the list of listeners to be notified when the event of a user clicking on the map occurs. The following piece of setProperties does all of this:

if (actionListener != null) {
        new MethodExpressionActionListener(actionListener));

If your component fires value change events, your tag handler’s setProperties method does a similar thing, except it wraps the expression in a MethodExpressionValueChangeListener object and adds the listener using the addValueChangeListener method.

In the case of the method expression referenced by the action attribute, the setProperties method uses the setActionExpression method of ActionSource2 to set the corresponding property on MapComponent:

if (action != null) {