Using the Standard Converters

The JavaServer Faces implementation provides a set of Converter implementations that you can use to convert component data. The purpose of conversion is to take the String-based data coming in from the Servlet API and convert it to strongly typed Java objects suitable for the business domain. For more information on the conceptual details of the conversion model, see Conversion Model.

The standard Converter implementations are located in the javax.faces.convert package. Normally, converters are implicitly assigned based on the type of the EL expression pointed to by the value of the component. However, these converters can also be accessed by a converter ID. Table 11-1 shows the converter classes and their associated converter IDs.

Table 11-1 Converter Classes and Converter IDs

Class in the javax.faces.convert Package

Converter ID

BigDecimalConverter

javax.faces.BigDecimal

BigIntegerConverter

javax.faces.BigInteger

BooleanConverter

javax.faces.Boolean

ByteConverter

javax.faces.Byte

CharacterConverter

javax.faces.Character

DateTimeConverter

javax.faces.DateTime

DoubleConverter

javax.faces.Double

EnumConverter

javax.faces.Enum

FloatConverter

javax.faces.Float

IntegerConverter

javax.faces.Integer

LongConverter

javax.faces.Long

NumberConverter

javax.faces.Number

ShortConverter

javax.faces.Short

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 f:convertDateTime and f:convertNumber, which are described in Using DateTimeConverter and Using NumberConverter, respectively.
Bind the value of the component to a managed bean property of the same type as the converter. This is the most common technique.
Refer to the converter from the component tag’s converter attribute, specifying the ID of the converter class.
Nest an f:converter tag inside of the component tag, and use either the f:converter tag’s converterId attribute or its binding attribute to refer to the converter.

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

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

The data from the h: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 f: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.

You can also nest an f: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 that uses one of the converter IDs listed in Table 11-1:

<h:inputText value="#{loginBean.age}">
    <f:converter converterId="javax.faces.Integer" />
</h:inputText>

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

You can also create custom converters and register them on components using the f:converter tag. For details, see Creating and Using a Custom Converter.

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 11-2 lists the attributes.

Here is a simple example of a convertDateTime tag:

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

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

The example tag can display the following output:

Saturday, September 21, 2013

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

<h:outputText value="#{cashierBean.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:outputText value="#{cashierBean.shipDate}">
    <f:convertDateTime dateStyle="full"
                       locale="es"
                       timeStyle="long" type="both" />
</h:outputText>

This tag would display the following output:

jueves 24 de octubre de 2013 15:07:04 GMT

Refer to the "Customizing Formats" lesson of the Java Tutorial at http://docs.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.

Table 11-2 Attributes for the f:convertDateTime Tag

Attribute

Type

Description

binding

DateTimeConverter

Used to bind a converter to a managed 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 if pattern is not defined. Valid values: default, short, medium, long, and full. If no value is specified, default is used.

for

String

Used with composite components. Refers to one of the objects within the composite component inside which this tag is nested.

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 and timeStyle attributes are ignored.

See Table 11-3 for the default values when pattern is not specified.

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, both, LocalDate, LocalTime, LocalDateTime, OffsetTime, OffsetDateTime, or ZonedDateTime. If no value is specified, date is used.

See Table 11-3 for additional information.

Table 11-3 Type Attribute and Default Pattern Values

Type Attribute

Class

Default When Pattern Is Not Specified

both

java.util.Date

DateFormat.getDateTimeInstance(dateStyle, timeStyle)

date

java.util.Date

DateFormat.getDateTimeInstance(dateStyle)

time

java.util.Date

DateFormat.getDateTimeInstance(timeStyle)

localDate

java.time.LocalDate

DateTimeFormatter.ofLocalizedDate(dateStyle)

localTime

java.time.LocalTime

DateTimeFormatter.ofLocalizedTime(dateStyle)

localDateTime

java.time.LocalDateTime

DateTimeFormatter.ofLocalizedDateTime(dateStyle)

offsetTime

java.time.OffsetTime

DateTimeFormatter.ISO_OFFSET_TIME

offsetDateTime

java.time.OffsetDateTime

DateTimeFormatter.ISO_OFFSET_DATE_TIME

zonedDateTime

java.time.ZonedDateTime

DateTimeFormatter.ISO_ZONED_DATE_TIME

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 11-4 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 currencySymbol="$" type="currency"/>
</h:outputText>

When binding the NumberConverter to a component, ensure that the managed 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 double.

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

$934

This result can also be displayed by using the following tag in which 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://docs.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.

Table 11-4 Attributes for the f:convertNumber Tag

Attribute

Type

Description

binding

NumberConverter

Used to bind a converter to a managed bean property.

currencyCode

String

ISO 4217 currency code, used only when formatting currencies.

currencySymbol

String

Currency symbol, applied only when formatting currencies.

for

String

Used with composite components. Refers to one of the objects within the composite component inside which this tag is nested.

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.