Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial

## 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.

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