Using the Standard Converters - The J2EE 1.4 Tutorial

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.

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

Two of these standard converters (DateTimeConverter and NumberConverter) have their own tags, which allow you to configure the format of the component data by configuring the tag attributes. Using DateTimeConverter discusses using DateTimeConverter. Using NumberConverter discusses using NumberConverter.

You can use the other standard converters in one of three ways:

You can make sure that the component that uses the converter has its value bound to a backing bean property of the same type as the converter.
You can refer to the converter by class or by its ID using the component tag's converter attribute. The ID is defined in the application configuration resource file (see Application Configuration Resource File).
You can refer to the converter by its ID using the converterId attribute of the converter tag.

The latter two will convert the component's local value. The first method will convert the model value of the component. For example, if you want a component's data to be converted to an Integer, you can bind the component to a property similar to this:

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

Alternatively, if the component is not bound to a bean property, you can use the converter attribute on the component tag:

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

The data corresponding to this 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 refer to the converter's ID via the converter tag's converterId attribute. If the tag is referring to a custom converter, the value of converterID must match the ID in the application configuration resource file. Here is an example:

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

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 18-5 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 18-5 convertDateTime Tag Attributes 

Attribute	Type	Description
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 18-6 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 18-6 convertNumber Attributes  

Attribute	Type	Description
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.
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.
locale	String or Locale	Locale whose number styles are used to format or parse data.
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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