Bean validation involves validating user input using Tapestry's built-in support for the JSR 303 Bean Validation API.
Tapestry has always provided a powerful non-JSR 303 validation mechanism (see Forms and Validation). Among other things this mechanism allows you to annotate your domain model classes with the @Validate annotation. However, this annotation is problematic if your domain model is used in non-Tapestry applications as well as in Tapestry applications. Your non-Tapestry application becomes dependent on tapestry5-annotations module. To make your domain model independent from Tapestry you can use the JSR 303: Bean Validation instead. This library provides integration between Tapestry and JSR-303.
The Tapestry's JSR 303 - Bean Validation Library is responsible for configuring and bootstrapping the Validator for you. In order to use this library you have to choose an implementation of the JSR-303 specification like Hibernate Validator 4.x. This library is not specific to any implementation of JSR-303 and will work with any implementation of your choice.
Bootstraping the Bean Validator
The BeanValidatorSource service is responsible for bootstrapping the Validator. You can contribute a BeanValidatorConfigurer to the configuration of this service in order to participate on the configuration of Validator.
In JSR-303 validation groups are used to define a subset of the constraints validated at a given time. If no validation group is specified the Default group is taken. By default, Tapestry passes only this group to Validator. You can tell Tapestry to pass more groups by contributing group classes into the configuration of the BeanValidatorSource service.
Validating Input Fields
Once you included this library and its dependencies into your web app, you may use the JSR-303 annotations to validate the user's input.
You can even mix JSR-303 annotations and Tapestry's @Validate annotation.
Next you have to pass the object to validate into the Form's validate parameter. In the following example the Form's fields are bound to the properties of the Login page. That's why we pass this, thus the page instance, to the validate parameter.
Since the validate parameter defaults to the container of the Form component, we could also remove validate="this" in the example above.
Validating Beans with BeanEditForm
If you use the BeanEditForm component it's even easier to validate your beans. The only thing you have to do is to annotate your beans with JSR-303 annotations. If you are migrating from Tapestry's built-in validation mechanism to JSR-303 Bean Validation, you don't have to change your template at all.
Unfortunately JSR-303 doesn’t cover client-side validation, so web frameworks supporting this JSR need to come up with proprietary client-side solutions. Tapestry provides client-side validation for the following JSR-303 constraints:
Providing own client-side validators
Now let's see how to provide own client-side validation for JSR-303 constraints. Imagine you created the following constraint definition. The server-side implementation of the constraint is implemented by RangeValidator. I suppose you are familiar with JSR-303, so we won't explain how to implement RangeValidator.
- Field being validated
- Validation message
- JSON object with values from the constraint annotation
Here is an example:
Now you have to tell Tapestry to call the function Tapestry.Validator.range when client-side validation of @Range should be executed. This is accomplished by a contribution to the ClientConstraintDescriptorSource service. The configuration of this service is a collection of ClientConstraintDescriptor. Each ClientConstraintDescriptor represents a client-side validation constraint. The constructor of ClientConstraintDescriptor has three parameters:
- Class of the constraint annotation.