Using the Standard Validators

Validating a Component's Value

Using theLongRangeValidator

Using the Standard Validators

JavaServer Faces technology provides a set of standard classes and associated tags thatpage authors and application developers can use to validate a component’s data.Table 11-7lists all the standard validator classes and the tags that allow you touse the validators from the page.

Table 11-7 The Validator Classes

All these validator classes implement theValidator interface. Component writers and application developerscan also implement this interface to define their own set of constraints fora component’s value.

Similarly to the standard converters, each of these validators has one or morestandard error messages associated with it. If you have registered one of thesevalidators onto a component on your page, and the validator is not ableto validate the component’s value, the validator’s error message will display on thepage. For example, the error message that displays when the component’s value exceedsthe maximum value allowed byLongRangeValidator is the following:

{1}: Validation Error: Value is greater than allowable maximum of "{0}"

In this case the{1} substitution parameter is replaced by the component’s labelor ID, and the{0} substitution parameter is replaced with the maximum valueallowed by the validator.

See section 2.5.4 of the JavaServer Faces specification for the complete list oferror messages. SeeDisplaying Error Messages with themessage andmessages Tags for information on how to display validation error messageson the page when validation fails.

Validating a Component’s Value

In order to validate a component’s value using a particular validator, you needto register the validator on the component. You have three ways to dothis:

• Nest the validator’s corresponding tag (shown inTable 11-7) inside the component’s tag.Using theLongRangeValidator describes how to use thevalidateLongRange tag. You can use the other standard tags in the same way.

• Refer to a method that performs the validation from the component tag’svalidator attribute.

• Nest avalidator tag inside the component tag and use either the validator tag’svalidatorId attribute or itsbinding attribute to refer to the validator.

SeeReferencing a Method That Performs ValidationReferencing a Method That Performs Validation for more information on using thevalidator attribute.

ThevalidatorId attribute works similarly to theconverterId attribute of theconvertertag, as described inConverting a Component's Value. SeeBinding Converters, Listeners, and Validators to Backing Bean Properties for more information on using thebindingattribute of thevalidator tag.

Keep in mind that validation can be performed only on components that implementEditableValueHolder because these components accept values that can be validated.

Using theLongRangeValidator

The Duke’s Bookstore application uses avalidateLongRange tag on thequantity input field ofthebookshowcart.jsp page:

<h:inputText size="4"     value="#{item.quantity}" >    <f:validateLongRange minimum="1"/></h:inputText><h:message for="quantity"/>

This tag requires that the user enter a number that is atleast 1. Thesize attribute specifies that the number can have nomore than four digits. ThevalidateLongRange tag also has amaximum attribute, with whichyou can set a maximum value of the input.

The attributes of all the standard validator tags accept value expressions. This meansthat the attributes can reference backing bean properties rather than specify literal values.For example, thevalidateLongRange tag in the preceding example can reference a backingbean property calledminimum to get the minimum value acceptable to thevalidator implementation:

<f:validateLongRange minimum="#{ShowCartBean.minimum}" />

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