Bean Validation

Added in 5.2

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Integrate JSR 303 - Bean Validation API

Tapestry provides a powerful validation mechanism (see Forms and Validation). Among other things this mechanism allows you to annotate your domain model classes with the @Validate annotation. 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. This library provides integration between Tapestry and JSR-303.

Configuration

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.

Validation groups

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.

Usage

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.

Client-side Validation

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:

JSR-303 constraint

Tapestry' JavaScript function

@Max

Tapestry.Validator.maxnumber

@Min

Tapestry.Validator.minnumber

@NotNull

Tapestry.Validator.notnull

@Null

Tapestry.Validator.isnull

@Pattern

Tapestry.Validator.pattern

@Size

Tapestry.Validator.size

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 I don’t explain how to implement RangeValidator.

To provide client-side validation of a constraint you have to add a JavaScript function to the built-in Tapestry.Validator JavaScript-object. The function should contain exactly three parameters:

  1. Field being validated
  2. Validation message
  3. 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:

  1. Class of the constraint annotation.
  2. Name of the JavaScript function.
  3. The last parameter is a varargs. It is used to pass the attribute names of the constraint annotation to be passed (along with their values) to the JavaScript function as an JSON object.

The last step is to make the contribution, which links the @Range annotation with the JavaScript function range. The attributes max and min and their values are passed to the function.