JSF Under the Hood—Part 1 - JSF and HTML5 - page 45

public void beverageSelected(ValueChangeEvent event) {
String selectedBeverage = event.getNewValue().toString();
if ("tea".equals(selectedBeverage)) {
price = 2.0;
} else if ("coffee".equals(selectedBeverage)) {
price = 2.5;
} else if ("cocacola".equals(selectedBeverage)) {
price = 3.0;
}
}

}

As shown in Listing 2-22, the method of the valueChangeListener attribute has the following signature:

void . • Returns

ValueChangeEvent object.
The ValueChangeEvent object holds both the old value and the new selected value. The new selected value can
be retrieved using getNewValue() . In the beverageSelected method, the new selected value is retrieved and a price is
set according to the selected beverage item. Figure 2-3 shows the beverages example output.

• Takes a single argument which is the

Figure 2-3. The beverages example output

So far, we have seen two examples of the JSF method expressions; in the following chapters, we will see many
other examples.

■ You do not have make a full page submission in order to execute the valueChangeListener method of the
EditableValueHolder ; otherwise, you can use the <f:ajax> tag in order to invoke the valueChangeListener method in
an ajaxified style (the <f:ajax> tag will be discussed in detail in Chapter 5).

Note

It is important to note that if you are working on a Java EE 6 container (or later) which includes the Unified EL
2.1, you can invoke arbitrary methods with parameters. Let's see an example to explain this. Listing 2-23 shows the
calculateAverage method of a custom Maths managed bean.

Listing 2-23. The calculateAverage Method of a Custom Maths Managed Bean

@ManagedBean
@RequestScoped
public class Maths {

public Double calculateAverage (Double number1, Double number2) {
return (number1 + number2) / 2;
}
}