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Details on Using Bean Validation from JSF
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Let s now look more closely at the details associated with bean validation At the core of the process is the concept of a constraint In bean validation, a constraint is a Java annotation that is annotated with the annotation javaxvalidationConstraint The definition of the @Email constraint from the example is shown here The @Constraint annotation is shown in boldface The validatedBy attribute will be explained shortly
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package comjsfcompref; import import import import import import javalangannotationDocumented; javalangannotationElementType; javalangannotationRetention; javalangannotationRetentionPolicy; javalangannotationTarget; javaxvalidationConstraint;
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@Documented @Constraint(validatedBy = EmailConstraintValidatorclass) @Target({ElementTypeMETHOD, ElementTypeFIELD}) @Retention(RetentionPolicyRUNTIME) public @interface Email { String message() default "{validatoremail}"; Class< >[] groups() default {}; Class< extends ConstraintPayload>[] payload() default {}; }
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The act of using a Constraint on a POJO is called a constraint declaration Taking an excerpt from the UserBean in the preceding section, it looks like this
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@Email protected String email;
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This is exactly analogous to the use of the e-mail validator on the <h:inputText> field in the registrationxhtml page, as shown here:
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<h:inputText label="Email Address" id="email" value="#{userBeanemail}" required="true" validator="#{userBeanvalidateEmail}"/>
In both cases, we are declaring that the e-mail field should be validated by a piece of code that answers the question, is this data a valid e-mail address In bean validation, that code lives in the class (or classes) listed on the right-hand side of the validatedBy attribute within the @Constraint annotation Such a class must implement the ConstraintValidator interface, which uses generics for maximal type safety This is called a ConstraintValidator implementation The EmailConstraintValidator class looks like this:
package comjsfcompref; import javaxvalidationConstraintValidator; import javaxvalidationConstraintValidatorContext; public class EmailConstraintValidator implements ConstraintValidator<Email, String> { public void initialize(Email parameters) { } public boolean isValid(String value, ConstraintValidatorContext ctxt) { boolean result = true; if (-1 == valueindexOf("@")) { result = false; } return result; } }
It is very important to understand the use of generics in this class declaration
public class EmailConstraintValidator implements ConstraintValidator<Email, String> {
The first generic must be the actual annotation that is annotated with @Constraint, in this case Email The second generic is the type of the value that is to be validated The initialize( ) method will always be called before isValid( ) and can be used to perform any setup
8:
C o n v e r t i n g a n d Va l i d a t i n g D a t a
necessary for the forthcoming validation The isValid( ) method is exactly analogous to our validator method in the original JSFReg version of UserBean In fact, the code was copied and pasted directly The only change is that, instead of throwing a ValidatorException, the isValid( ) method returns true if the value is valid, and returns false otherwise The last remaining difference to explore is how the validation messages get defined and placed into the view You will see how to do this in the context of Faces messages, later in the chapter, but for now just know that the line
String message() default "{validatoremail}";
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on the Email annotation can either be a resource bundle key enclosed with { }, or an actual literal string, such as
String message() default "You must include a valid email";
Now that you know what a Constraint is, and how to define a ConstraintValidator implementation for it, it s time to show how these are used with JSF
Validating JSF Managed Bean Properties with Bean Validation
Like Ed Burns for JSF, Emmanuel Bernard, the team leader for the bean validation specification, was very keen on reducing or eliminating any extra configuration that users must do in order to use his technology Emmanuel devised a new feature in JSF, the defaultvalidators, and declared some rules about how this new feature was to be used in the case of bean validation This element can be included within the existing <application /> element The syntax for this element looks like this:
<faces-config> <application> <default-validators> <validator-id>whatevervalidatoridyouwant</validator-id> </default-validators> </application> </faces-config>
Any validators declared in this way are automatically added to every EditableValueHolder component, on every page in the application The magic with respect to bean validation is that if you are running in a container that supports bean validation, the javaxfacesBean validator is automatically included among the defaultvalidators Because of the way the javaxfacesBean validator is defined, this means any fields annotated with bean validation Constraints that are pointed to by EL expressions in the Facelet page are automatically validated according to those Constraints For example, the JSFReg e-mail field that previously looked like this:
<h:inputText label="Email Address" id="email" value="#{userBeanemail}" required="true" validator="#{userBeanvalidateEmail}"/>
can simply be rewritten as this:
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