Using the Standard Validators

JavaServer Faces technology provides a set of standard classes and associated tags that page authors and application developers can use to validate a component’s data. Table 8-3 lists all the standard validator classes and the tags that allow you to use the validators from the page.

Table 8-3 The Validator Classes

Validator Class	Tag	Function
`DoubleRangeValidator`	`validateDoubleRange`	Checks whether the local value of a component is within a certain range. The value must be floating-point or convertible to floating-point.
`LengthValidator`	`validateLength`	Checks whether the length of a component’s local value is within a certain range. The value must be a `java.lang.String`.
`LongRangeValidator`	`validateLongRange`	Checks whether the local value of a component is within a certain range. The value must be any numeric type or `String` that can be converted to a `long`.
`RegexValidator`	`validateRegEx`	Checks whether the local value of a component is a match against a regular expression from `java.util.regex` package.
`BeanValidator`	`validateBean`	Registers a bean validator for the component
`RequiredValidator`	`validateRequired`	Ensures that the local value is not empty on a `EditableValueHolder` component

Similar to the standard converters, each of these validators has one or more standard error messages associated with it. If you have registered one of these validators onto a component on your page, and the validator is unable to validate the component’s value, the validator’s error message will display on the page. For example, the error message that displays when the component’s value exceeds the maximum value allowed by LongRangeValidator is as follows:

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

In this case, the {1} substitution parameter is replaced by the component’s label or id, and the {0} substitution parameter is replaced with the maximum value allowed by the validator.

Validating a Component’s Value

To validate a component’s value using a particular validator, you need to register that validator on the component. You can do this in one of the following ways:

Nest the validator’s corresponding tag (shown in Table 8-3) inside the component’s tag. Using the LongRangeValidator describes how to use the validateLongRange tag. You can use the other standard tags in the same way.
Refer to a method that performs the validation from the component tag’s validator attribute.
Nest a validator tag inside the component tag and use either the validator tag’s validatorId attribute or its binding attribute to refer to the validator.

See Referencing a Method That Performs Validation for more information on using the validator attribute.

The validatorId attribute works similarly to the converterId attribute of the converter tag, as described in Converting a Component's Value.

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

Using the `LongRangeValidator`

The following example shows how to use the validateLongRange validator on a input component tag quantity:

<h:inputText id="quantity" 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 at least 1. The size attribute specifies that the number can have no more than four digits. The validateLongRange tag also has a maximum attribute, with which you can set a maximum value of the input.

The attributes of all the standard validator tags accept EL value expressions. This means that the attributes can reference backing bean properties rather than specify literal values. For example, the validateLongRange tag in the preceding example can reference a backing bean property called minimum to get the minimum value acceptable to the validator implementation as shown here:

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