The Java EE 5 Tutorial

Setting Component Property Values

After retrieving the type of the component, the tag handler sets the component’s property values to those supplied as tag attributes values in the page. This section assumes that your component properties are enabled to accept expressions, as explained in Enabling Component Properties to Accept Expressions.

Getting the Attribute Values

Before setting the values in the component class, the MapTag handler first gets the attribute values from the page by means of JavaBeans component properties that correspond to the attributes. The following code shows the property used to access the value of the immediate attribute.

private javax.el.ValueExpression immediate = null;

public void setImmediate(javax.el.ValueExpression immediate)
    this.immediate = immediate;

As this code shows, the setImmediate method takes a ValueExpression object. This means that the immediate attribute of the map tag accepts value expressions.

Similarly, the setActionListener and setAction methods take MethodExpression objects, which means that these attributes accept method expressions. The following code shows the properties used to access the values of the actionListener and the action attributes

private javax.el.MethodExpression actionListener = null;

public void setActionListener(
    javax.el.MethodExpression actionListener) {
    this.actionListener = actionListener;
private javax.el.MethodExpression action = null;

public void setAction(javax.el.MethodExpression action) {
        this.action = action;

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) {