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Using the Standard Converters

The JavaServer Faces implementation provides a set of Converter implementations that you can use to convert component data. For more information on the conceptual details of the conversion model, see Conversion Model (page 289).

The standard Converter implementations, located in the javax.faces.convert package, are as follows:

BigDecimalConverter
BigIntegerConverter
BooleanConverter
ByteConverter
CharacterConverter
DateTimeConverter
DoubleConverter
FloatConverter
IntegerConverter
LongConverter
NumberConverter
ShortConverter

Each of these converters has a standard error message associated with them. 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 error message that displays if BigIntegerConverter fails to convert a value is:

{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. See section 2.4.5 of the JavaServer Faces specification, version 1.2, for a complete list of error messages.

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. Using DateTimeConverter discusses using DateTimeConverter. Using NumberConverter discusses using NumberConverter. The following section explains how to convert a component's value including how to register the other standard converters with a component.

Converting a Component's Value

You can register any of the standard converters on a component in one of three ways:

Bind the value of the component to a backing bean property of the same type as the converter.
Refer to the converter by class or by its ID using 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 first approach, if you want a component's data to be converted to an Integer, you can simply bind the component's value to a property similar to this:

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 employ the second technique by using the converter attribute 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. If the converter is a custom converter, the ID is defined in the application configuration resource file (see Application Configuration Resource File, page 448).

The data corresponding to this example inputText tag will be converted to a java.lang.Integer. Notice that the Integer type is already a supported type of the NumberConverter. If you don't need to specify any formatting instructions using the convertNumber tag attributes, and if one of the other converters will suffice, you can simply reference that converter 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. Again, if the converter is a custom converter, the value of converterID must match the ID in the application configuration resource file; otherwise it must match the ID as defined in the converter class. 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. For example, consider this example:

<h:inputText value="#{LoginBean.Age}" />
  <f:converter binding="#{Employee.convertAge}" />
</h:inputText> 

In this case, the binding attribute references a property called convertAge in the bean, Employee. If the converter is supposed to be an IntegerConverter instance then the convertAge property would look like this:

private IntegerConverter convertAge;

public IntegerConverter getConvertAge(){ return convertAge;}

public void setConvertAge(IntegerConverter convertAge) {this.convertAge = convertAge;} 

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 10-5 lists the attributes.

Here is a simple example of a convertDateTime tag from the bookreceipt.jsp page:

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

Here is an example of a date and time that this tag can display:

Saturday, Feb 22, 2003 

You can also display the same date and time using this tag:

<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

Sabado, Feb 22, 2003 

Please refer to the Customizing Formats lesson of the Java Tutorial at
http://java.sun.com/docs/books/tutorial/i18n/format/simpleDateFormat.html for more information on how to format the output using the pattern attribute of the convertDateTime tag.

Table 10-5 convertDateTime Tag Attributes 

Attribute	Type	Description
binding	DateTimeConverter	Used to bind a converter to a backing bean property
dateStyle	String	Defines the format, as specified by java.text.DateFormat, of a date or the date part of a date string. Applied only if type is date (or both) and pattern is not defined. Valid values: default, short, medium, long, and full. If no value is specified, default is used.
locale	String or Locale	Locale whose predefined styles for dates and times are used during formatting or parsing. If not specified, the Locale returned by FacesContext.getLocale will be used.
pattern	String	Custom formatting pattern that determines how the date/time string should be formatted and parsed. If this attribute is specified, dateStyle, timeStyle, and type attributes are ignored.
timeStyle	String	Defines the format, as specified by java.text.DateFormat, of a time or the time part of a date string. Applied only if type is time and pattern is not defined. Valid values: default, short, medium, long, and full. If no value is specified, default is used.
timeZone	String or TimeZone	Time zone in which to interpret any time information in the date string.
type	String	Specifies whether the string value will contain a date, a time, or both. Valid values are date, time, or both. If no value is specified, date is used.

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 10-6 lists the attributes.

The bookcashier.jsp page of Duke's Bookstore uses a convertNumber tag to display the total prices of the books in the shopping cart:

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

Here is an example of a number this tag can display

$934 

This number can also be displayed using this tag:

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

Please refer to the Customizing Formats lesson of the Java Tutorial at
http://java.sun.com/docs/books/tutorial/i18n/format/decimalFormat.html for more information on how to format the output using the pattern attribute of the convertNumber tag.

Table 10-6 convertNumber Attributes  

Attribute	Type	Description
binding	NumberConverter	Used to bind a converter to a backing bean property
currencyCode	String	ISO4217 currency code, used only when formatting currencies.
currencySymbol	String	Currency symbol, applied only when formatting currencies.
groupingUsed	boolean	Specifies whether formatted output contains grouping separators.
integerOnly	boolean	Specifies whether only the integer part of the value will be parsed.
locale	String or Locale	Locale whose number styles are used to format or parse data.
maxFractionDigits	int	Maximum number of digits formatted in the fractional part of the output.
maxIntegerDigits	int	Maximum number of digits formatted in the integer part of the output.
minFractionDigits	int	Minimum number of digits formatted in the fractional part of the output.
minIntegerDigits	int	Minimum number of digits formatted in the integer part of the output.
pattern	String	Custom formatting pattern that determines how the number string is formatted and parsed.
type	String	Specifies whether the string value is parsed and formatted as a number, currency, or percentage. If not specified, number is used.

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