Using the Standard Converters

The JavaServer Faces implementation provides a set of Converter implementations that you can use to convert component data. The standard Converter implementations, located in the javax.faces.convert package, are as follows:

• BigDecimalConverter

• BigIntegerConverter

• BooleanConverter

• ByteConverter

• CharacterConverter

• DateTimeConverter

• DoubleConverter

• EnumConverter

• FloatConverter

• IntegerConverter

• LongConverter

• NumberConverter

• ShortConverter

A standard error message is associated with each of these converters. If you have registered one of these converters onto a component on your page, and the converter is not able to convert the component’s value, the converter’s error message will display on the page. For example, the following error message appears if BigIntegerConverter fails to convert a value:

{0} must be a number consisting of one or more digits

In this case, the {0} substitution parameter will be replaced with the name of the input component on which the converter is registered.

Two of the standard converters (DateTimeConverter and NumberConverter) have their own tags, which allow you to configure the format of the component data using the tag attributes. For more information about using DateTimeConverter, see Using DateTimeConverter. For more information about using NumberConverter, see Using NumberConverter. The following section explains how to convert a component’s value, including how to register other standard converters with a component.

Converting a Component’s Value

To use a particular converter to convert a component’s value, you need to register the converter onto the component. You can register any of the standard converters in one of the following ways:

• Nest one of the standard converter tags inside the component’s tag. These tags are convertDateTime and convertNumber, which are described in Using DateTimeConverter and Using NumberConverter, respectively.

• Bind the value of the component to a backing bean property of the same type as the converter.

• Refer to the converter from the component tag’s converter attribute.

• Nest a converter tag inside of the component tag, and use either the converter tag’s converterId attribute or its binding attribute to refer to the converter.

As an example of the second method, if you want a component’s data to be converted to an Integer, you can simply bind the component’s value to a backing bean property. Here is an example:

Integer age = 0;
public Integer getAge(){ return age;}
public void setAge(Integer age) {this.age = age;}

If the component is not bound to a bean property, you can use the third method by using the converter attribute directly on the component tag:

<h:inputText
    converter="javax.faces.convert.IntegerConverter" />

This example shows the converter attribute referring to the fully qualified class name of the converter. The converter attribute can also take the ID of the component.

The data from the inputText tag in the this example will be converted to a java.lang.Integer value. The Integer type is a supported type of NumberConverter. If you don’t need to specify any formatting instructions using the convertNumber tag attributes, and if one of the standard converters will suffice, you can simply reference that converter by using the component tag’s converter attribute.

Finally, you can nest a converter tag within the component tag and use either the converter tag’s converterId attribute or its binding attribute to reference the converter.

The converterId attribute must reference the converter’s ID. Here is an example:

<h:inputText value="#{LoginBean.Age}" />
    <f:converter converterId="Integer" />
</h:inputText>

Instead of using the converterId attribute, the converter tag can use the binding attribute. The binding attribute must resolve to a bean property that accepts and returns an appropriate Converter instance.

Using DateTimeConverter

You can convert a component’s data to a java.util.Date by nesting the convertDateTime tag inside the component tag. The convertDateTime tag has several attributes that allow you to specify the format and type of the data. Table 8–1 lists the attributes.

Here is a simple example of a convertDateTime tag:

<h:outputText id= "shipDate" value="#{cashier.shipDate}">
    <f:convertDateTime dateStyle="full" />
</h:outputText>

When binding the DateTimeConverter to a component, ensure that the backing bean property to which the component is bound is of type java.util.Date. In the preceding example, cashier.shipDate must be of type java.util.Date.

The example tag can display the following output:

Saturday, September 25, 2010

You can also display the same date and time by using the following tag where the date format is specified:

<h:outputText value="#{cashier.shipDate}">
    <f:convertDateTime
         pattern="EEEEEEEE, MMM dd, yyyy" />
</h:outputText>

If you want to display the example date in Spanish, you can use the locale attribute:

<h:inputText value="#{cashier.shipDate}">
    <f:convertDateTime dateStyle="full"
        locale="Locale.SPAIN"
        timeStyle="long" type="both" />
</h:inputText>

This tag would display the following output:

sabado 25 de septiembre de 2010

Refer to the “Customizing Formats” lesson of the Java Tutorial at http://download.oracle.com/javase/tutorial/i18n/format/simpleDateFormat.html for more information on how to format the output using the pattern attribute of the convertDateTime tag.

Using NumberConverter

You can convert a component’s data to a java.lang.Number by nesting the convertNumber tag inside the component tag. The convertNumber tag has several attributes that allow you to specify the format and type of the data. Table 8–2 lists the attributes.

The following example uses a convertNumber tag to display the total prices of the contents of a shopping cart:

<h:outputText value="#{cart.total}" >
    <f:convertNumber type="currency"/>
</h:outputText>

When binding the NumberConverter to a component, ensure that the backing bean property to which the component is bound is of a primitive type or has a type of java.lang.Number. In the preceding example, cart.total is of type java.lang.Number.

Here is an example of a number that this tag can display:

$934

This result can also be displayed by using the following tag, where the currency pattern is specified:

<h:outputText id="cartTotal"
     value="#{cart.Total}" >
    <f:convertNumber pattern="$####" />
</h:outputText>

See the “Customizing Formats” lesson of the Java Tutorial at http://download.oracle.com/javase/tutorial/i18n/format/decimalFormat.html for more information on how to format the output by using the pattern attribute of the convertNumber tag.