Chapter 20. Bean Validation Support
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# Chapter 20. Bean Validation Support

Validation is a process of verifying that some data obeys one or more pre-defined constraints. This chapter describes support for Bean Validation in Jersey in terms of the needed dependencies, configuration, registration and usage. For more detailed description on how JAX-RS provides native support for validating resource classes based on the Bean Validation refer to the chapter in the JAX-RS spec.

## 20.1. Bean Validation Dependencies

Bean Validation support in Jersey is provided as an extension module and needs to be mentioned explicitly in your `pom.xml` file (in case of using Maven):

    <dependency>
        <groupId>org.glassfish.jersey.ext</groupId>
        <artifactId>jersey-bean-validation</artifactId>
        <version>3.0.17</version>
    </dependency>

### Note

If you're not using Maven make sure to have also all the transitive dependencies (see jersey-bean-validation) on the classpath.

This module depends directly on Hibernate Validator which provides a most commonly used implementation of the Bean Validation API spec.

If you want to use a different implementation of the Bean Validation API, use standard Maven mechanisms to exclude Hibernate Validator from the modules dependencies and add a dependency of your own.

    <dependency>
        <groupId>org.glassfish.jersey.ext</groupId>
        <artifactId>jersey-bean-validation</artifactId>
        <version>3.0.17</version>
        <exclusions>
            <exclusion>
                <groupId>org.hibernate</groupId>
                <artifactId>hibernate-validator</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

## 20.2. Enabling Bean Validation in Jersey

As stated in Section 4.3, “Auto-Discoverable Features”, Jersey Bean Validation is one of the modules where you don't need to explicitly register its `Feature`s (ValidationFeature) on the server as its features are automatically discovered and registered when you add the `jersey-bean-validation` module to your classpath. There are three Jersey specific properties that could disable automatic discovery and registration of Jersey Bean Validation integration module:

- CommonProperties.FEATURE_AUTO_DISCOVERY_DISABLE

- ServerProperties.FEATURE_AUTO_DISCOVERY_DISABLE

- ServerProperties.BV_FEATURE_DISABLE

### Note

Jersey does not support Bean Validation on the client at the moment.

## 20.3. Configuring Bean Validation Support

Configuration of Bean Validation support in Jersey is twofold - there are few specific properties that affects Jersey behaviour (e.g. sending validation error entities to the client) and then there is ValidationConfig class that configures Validator used for validating resources in JAX-RS application.

To configure Jersey specific behaviour you can use the following properties:

ServerProperties.BV_DISABLE_VALIDATE_ON_EXECUTABLE_OVERRIDE_CHECK

  Disables `@ValidateOnExecution` check. More on this is described in Section 20.5, “@ValidateOnExecution”.

ServerProperties.BV_SEND_ERROR_IN_RESPONSE

  Enables sending validation errors in response entity to the client. More on this in Section 20.7.1, “ValidationError”.

Example 20.1. Configuring Jersey specific properties for Bean Validation.

    new ResourceConfig()
        // Now you can expect validation errors to be sent to the client.
        .property(ServerProperties.BV_SEND_ERROR_IN_RESPONSE, true)
        // @ValidateOnExecution annotations on subclasses won't cause errors.
        .property(ServerProperties.BV_DISABLE_VALIDATE_ON_EXECUTABLE_OVERRIDE_CHECK, true)
        // Further configuration of ResourceConfig.
        .register( ... );

Customization of the `Validator` used in validation of resource classes/methods can be done using `ValidationConfig` class and exposing it via ContextResolver<T> mechanism as shown in Example 20.2, “Using `ValidationConfig` to configure `Validator`.”. You can set custom instances for the following interfaces from the Bean Validation API:

- MessageInterpolator - interpolates a given constraint violation message.

- TraversableResolver - determines if a property can be accessed by the Bean Validation provider.

- ConstraintValidatorFactory - instantiates a `ConstraintValidator` instance based off its class. Note that by setting a custom `ConstraintValidatorFactory` you may loose injection of available resources/providers at the moment. See Section 20.6, “Injecting” how to handle this.

- ParameterNameProvider - provides names for method and constructor parameters.

Example 20.2. Using `ValidationConfig` to configure `Validator`.

    /**
     * Custom configuration of validation. This configuration defines custom:
     * <ul>
     *     <li>ConstraintValidationFactory - so that validators are able to inject Jersey providers/resources.</li>
     *     <li>ParameterNameProvider - if method input parameters are invalid, this class returns actual parameter names
     *     instead of the default ones ({@code arg0, arg1, ..})</li>
     * </ul>
     */
    public class ValidationConfigurationContextResolver implements ContextResolver<ValidationConfig> {

        @Context
        private ResourceContext resourceContext;

        @Override
        public ValidationConfig getContext(final Class<?> type) {
            final ValidationConfig config = new ValidationConfig();
            config.setConstraintValidatorFactory(resourceContext.getResource(InjectingConstraintValidatorFactory.class));
            config.setParameterNameProvider(new CustomParameterNameProvider());
            return config;
        }

        /**
         * See ContactCardTest#testAddInvalidContact.
         */
        private class CustomParameterNameProvider implements ParameterNameProvider {

            private final ParameterNameProvider nameProvider;

            public CustomParameterNameProvider() {
                nameProvider = Validation.byDefaultProvider().configure().getDefaultParameterNameProvider();
            }

            @Override
            public List<String> getParameterNames(final Constructor<?> constructor) {
                return nameProvider.getParameterNames(constructor);
            }

            @Override
            public List<String> getParameterNames(final Method method) {
                // See ContactCardTest#testAddInvalidContact.
                if ("addContact".equals(method.getName())) {
                    return Arrays.asList("contact");
                }
                return nameProvider.getParameterNames(method);
            }
        }
    }

Register this class in your app:

    final Application application = new ResourceConfig()
            // Validation.
            .register(ValidationConfigurationContextResolver.class)
            // Further configuration.
            .register( ... );

### Note

This code snippet is based on CustomConfigValidationTest (from Jersey's source codes)

## 20.4. Validating JAX-RS resources and methods

JAX-RS specification states that constraint annotations are allowed in the same locations as the following annotations: `@MatrixParam`, `@QueryParam`, `@PathParam`, `@CookieParam`, `@HeaderParam` and `@Context`, except in class constructors and property setters. Specifically, they are allowed in resource method parameters, fields and property getters as well as resource classes, entity parameters and resource methods (return values). Jersey provides support for validation (see following sections) annotated input parameters and return value of the invoked resource method as well as validation of resource class (class constraints, field constraints) where this resource method is placed. Jersey does not support, and doesn't validate, constraints placed on constructors and Bean Validation groups (only `Default` group is supported at the moment).

### 20.4.1. Constraint Annotations

The JAX-RS Server API provides support for extracting request values and mapping them into Java fields, properties and parameters using annotations such as @HeaderParam, @QueryParam, etc. It also supports mapping of the request entity bodies into Java objects via non-annotated parameters (i.e., parameters without any JAX-RS annotations).

The Bean Validation specification supports the use of constraint annotations as a way of declarative validating beans, method parameters and method returned values. For example, consider resource class from Example 20.3, “Constraint annotations on input parameters” augmented with constraint annotations.

Example 20.3. Constraint annotations on input parameters

    @Path("/")
    class MyResourceClass {

        @POST
        @Consumes("application/x-www-form-urlencoded")
        public void registerUser(
                @NotNull @FormParam("firstName") String firstName,
                @NotNull @FormParam("lastName") String lastName,
                @Email @FormParam("email") String email) {
            ...
        }
    }

The annotations `@NotNull` and `@Email` impose additional constraints on the form parameters `firstName`, `lastName` and `email`. The `@NotNull` constraint is built-in to the Bean Validation API; the `@Email` constraint is assumed to be user defined in the example above. These constraint annotations are not restricted to method parameters, they can be used in any location in which JAX-RS binding annotations are allowed with the exception of constructors and property setters.

Rather than using method parameters, the `MyResourceClass` shown above could have been written as in Example 20.4, “Constraint annotations on fields”.

Example 20.4. Constraint annotations on fields

    @Path("/")
    class MyResourceClass {

        @NotNull
        @FormParam("firstName")
        private String firstName;

        @NotNull
        @FormParam("lastName")
        private String lastName;

        private String email;

        @FormParam("email")
        public void setEmail(String email) {
            this.email = email;
        }

        @Email
        public String getEmail() {
            return email;
        }

        ...
    }

Note that in this version, `firstName` and `lastName` are fields initialized via injection and `email` is a resource class property. Constraint annotations on properties are specified in their corresponding getters.

Constraint annotations are also allowed on resource classes. In addition to annotating fields and properties, an annotation can be defined for the entire class. Let us assume that `@NonEmptyNames` validates that one of the two name fields in `MyResourceClass` is provided. Using such an annotation, the example above can be extended to look like Example 20.5, “Constraint annotations on class”

Example 20.5. Constraint annotations on class

    @Path("/")
    @NonEmptyNames
    class MyResourceClass {

        @NotNull
        @FormParam("firstName")
        private String firstName;

        @NotNull
        @FormParam("lastName")
        private String lastName;

        private String email;

        ...
    }

Constraint annotations on resource classes are useful for defining cross-field and cross-property constraints.

### 20.4.2. Annotation constraints and Validators

Annotation constraints and validators are defined in accordance with the Bean Validation specification. The `@Email` annotation used in Example 20.4, “Constraint annotations on fields” is defined using the Bean Validation @Constraint meta-annotation, see Example 20.6, “Definition of a constraint annotation”.

Example 20.6. Definition of a constraint annotation

    @Target({ METHOD, FIELD, PARAMETER })
    @Retention(RUNTIME)
    @Constraint(validatedBy = EmailValidator.class)
    public @interface Email {

        String message() default "{com.example.validation.constraints.email}";

        Class<?>[] groups() default {};

        Class<? extends Payload>[] payload() default {};
    }

The `@Constraint` annotation must include a reference to the validator class that will be used to validate decorated values. The `EmailValidator` class must implement `ConstraintValidator<Email, T>` where `T` is the type of values being validated, as described in Example 20.7, “Validator implementation.”.

Example 20.7. Validator implementation.

    public class EmailValidator implements ConstraintValidator<Email, String> {

        public void initialize(Email email) {
            ...
        }

        public boolean isValid(String value, ConstraintValidatorContext context) {
            ...
        }
    }

Thus, `EmailValidator` applies to values annotated with `@Email` that are of type `String`. Validators for other Java types can be defined for the same constraint annotation.

### 20.4.3. Entity Validation

Request entity bodies can be mapped to resource method parameters. There are two ways in which these entities can be validated. If the request entity is mapped to a Java bean whose class is decorated with Bean Validation annotations, then validation can be enabled using @Valid as in Example 20.8, “Entity validation”.

Example 20.8. Entity validation

    @StandardUser
    class User {

        @NotNull
        private String firstName;

        ...
    }

    @Path("/")
    class MyResourceClass {

        @POST
        @Consumes("application/xml")
        public void registerUser(@Valid User user) {
            ...
        }
    }

In this case, the validator associated with `@StandardUser` (as well as those for non-class level constraints like `@NotNull`) will be called to verify the request entity mapped to `user`.

Alternatively, a new annotation can be defined and used directly on the resource method parameter (Example 20.9, “Entity validation 2”).

Example 20.9. Entity validation 2

    @Path("/")
    class MyResourceClass {

        @POST
        @Consumes("application/xml")
        public void registerUser(@PremiumUser User user) {
            ...
        }
    }

In the example above, `@PremiumUser` rather than `@StandardUser` will be used to validate the request entity. These two ways in which validation of entities can be triggered can also be combined by including `@Valid` in the list of constraints. The presence of `@Valid` will trigger validation of all the constraint annotations decorating a Java bean class.

Response entity bodies returned from resource methods can be validated in a similar manner by annotating the resource method itself. To exemplify, assuming both `@StandardUser` and `@PremiumUser` are required to be checked before returning a user, the `getUser` method can be annotated as shown in Example 20.10, “Response entity validation”.

Example 20.10. Response entity validation

    @Path("/")
    class MyResourceClass {

        @GET
        @Path("{id}")
        @Produces("application/xml")
        @Valid @PremiumUser
        public User getUser(@PathParam("id") String id) {
            User u = findUser(id);
            return u;
        }

        ...
    }

Note that `@PremiumUser` is explicitly listed and `@StandardUser` is triggered by the presence of the `@Valid` annotation - see definition of `User` class earlier in this section.

### 20.4.4. Annotation Inheritance

The rules for inheritance of constraint annotation are defined in Bean Validation specification. It is worth noting that these rules are incompatible with those defined by JAX-RS. Generally speaking, constraint annotations in Bean Validation are cumulative (can be strengthen) across a given type hierarchy while JAX-RS annotations are inherited or, overridden and ignored.

For Bean Validation annotations Jersey follows the constraint annotation rules defined in the Bean Validation specification.

## 20.5. @ValidateOnExecution

According to Bean Validation specification, validation is enabled by default only for the so called constrained methods. Getter methods as defined by the Java Beans specification are not constrained methods, so they will not be validated by default. The special annotation `@ValidateOnExecution` can be used to selectively enable and disable validation. For example, you can enable validation on method `getEmail` shown in Example 20.11, “Validate getter on execution”.

Example 20.11. Validate getter on execution

    @Path("/")
    class MyResourceClass {

        @Email
        @ValidateOnExecution
        public String getEmail() {
            return email;
        }

        ...
    }

The default value for the `type` attribute of `@ValidateOnExecution` is `IMPLICIT` which results in method `getEmail` being validated.

### Note

According to Bean Validation specification `@ValidateOnExecution` cannot be overridden once is declared on a method (i.e. in subclass/sub-interface) and in this situations a `ValidationException` should be raised. This default behaviour can be suppressed by setting ServerProperties.BV_DISABLE_VALIDATE_ON_EXECUTABLE_OVERRIDE_CHECK property (Jersey specific) to `true`.

## 20.6. Injecting

Jersey allows you to inject registered resources/providers into your ConstraintValidator implementation and you can inject Configuration, ValidatorFactory and Validator as required by Bean Validation spec.

### Note

Injected Configuration, ValidatorFactory and Validator do not inherit configuration provided by ValidationConfig and need to be configured manually.

Injection of JAX-RS components into `ConstraintValidator`s is supported via a custom `ConstraintValidatorFactory` provided by Jersey. An example is shown in Example 20.12, “Injecting UriInfo into a ConstraintValidator”.

Example 20.12. Injecting UriInfo into a ConstraintValidator

    public class EmailValidator implements ConstraintValidator<Email, String> {

        @Context
        private UriInfo uriInfo;

        public void initialize(Email email) {
            ...
        }

        public boolean isValid(String value, ConstraintValidatorContext context) {
            // Use UriInfo.

            ...
        }
    }

Using a custom ConstraintValidatorFactory of your own disables registration of the one provided by Jersey and injection support for resources/providers (if needed) has to be provided by this new implementation. Example 20.13, “Support for injecting Jersey's resources/providers via ConstraintValidatorFactory.” shows how this can be achieved.

Example 20.13. Support for injecting Jersey's resources/providers via ConstraintValidatorFactory.

    public class InjectingConstraintValidatorFactory implements ConstraintValidatorFactory {

        @Context
        private ResourceContext resourceContext;

        @Override
        public <T extends ConstraintValidator<?, ?>> T getInstance(final Class<T> key) {
            return resourceContext.getResource(key);
        }

        @Override
        public void releaseInstance(final ConstraintValidator<?, ?> instance) {
            // NOOP
        }
    }

### Note

This behaviour may likely change in one of the next version of Jersey to remove the need of manually providing support for injecting resources/providers from Jersey in your own `ConstraintValidatorFactory` implementation code.

## 20.7. Error Reporting

Bean Validation specification defines a small hierarchy of exceptions (they all inherit from ValidationException) that could be thrown during initialization of validation engine or (for our case more importantly) during validation of input/output values (ConstraintViolationException). If a thrown exception is a subclass of `ValidationException` except `ConstraintViolationException` then this exception is mapped to a HTTP response with status code 500 (Internal Server Error). On the other hand, when a `ConstraintViolationException` is throw two different status code would be returned:

- 500 (Internal Server Error)

  If the exception was thrown while validating a method return type.

- 400 (Bad Request)

  Otherwise.

### 20.7.1. ValidationError

By default, (during mapping `ConstraintViolationException`s) Jersey doesn't return any entities that would include validation errors to the client. This default behaviour could be changed by enabling ServerProperties.BV_SEND_ERROR_IN_RESPONSE property in your application (Example 20.1, “Configuring Jersey specific properties for Bean Validation.”). When this property is enabled then our custom ExceptionMapper<E extends Throwable> (that is handling `ValidationException`s) would transform `ConstraintViolationException`(s) into ValidationError(s) and set this object (collection) as the new response entity which Jersey is able to sent to the client. Four `MediaType`s are currently supported when sending `ValidationError`s to the client:

- `text/plain`

- `text/html`

- `application/xml`

- `application/json`

  ### Note

  Note: You need to register one of the JSON (JAXB) providers (e.g. MOXy) to marshall validation errors to JSON.

Let's take a look at ValidationError class to see which properties are send to the client:

    @XmlRootElement
    public final class ValidationError {

        private String message;

        private String messageTemplate;

        private String path;

        private String invalidValue;

        ...
    }

The `message` property is the interpolated error message, `messageTemplate` represents a non-interpolated error message (or key from your constraint definition e.g. `{jakarta.validation.constraints.NotNull.message}`), `path` contains information about the path in the validated object graph to the property holding invalid value and `invalidValue` is the string representation of the invalid value itself.

Here are few examples of `ValidationError` messages sent to client:

Example 20.14. `ValidationError` to `text/plain`

    HTTP/1.1 500 Internal Server Error
    Content-Length: 114
    Content-Type: text/plain
    Vary: Accept
    Server: Jetty(11.0.0.beta3)

    Contact with given ID does not exist. (path = ContactCardResource.getContact.<return value>, invalidValue = null)

Example 20.15. `ValidationError` to `text/html`

    HTTP/1.1 500 Internal Server Error
    Content-Length: ...
    Content-Type: text/plain
    Vary: Accept
    Server: Jetty(11.0.0.beta3)

    <div class="validation-errors">
        <div class="validation-error">
            <span class="message">Contact with given ID does not exist.</span>
            (
            <span class="path">
                <strong>path</strong>
                = ContactCardResource.getContact.<return value>
            </span>
            ,
            <span class="invalid-value">
                <strong>invalidValue</strong>
                = null
            </span>
            )
        </div>
    </div>

Example 20.16. `ValidationError` to `application/xml`

    HTTP/1.1 500 Internal Server Error
    Content-Length: ...
    Content-Type: text/plain
    Vary: Accept
    Server: Jetty(11.0.0.beta3)

    <?xml version="1.0" encoding="UTF-8"?>
    <validationErrors>
        <validationError>
            <message>Contact with given ID does not exist.</message>
            <messageTemplate>{contact.does.not.exist}</messageTemplate>
            <path>ContactCardResource.getContact.&lt;return value&gt;</path>
        </validationError>
    </validationErrors>

Example 20.17. `ValidationError` to `application/json`

    HTTP/1.1 500 Internal Server Error
    Content-Length: 174
    Content-Type: application/json
    Vary: Accept
    Server: Jetty(11.0.0.beta3)

    [ {
       "message" : "Contact with given ID does not exist.",
       "messageTemplate" : "{contact.does.not.exist}",
       "path" : "ContactCardResource.getContact.<return value>"
    } ]

## 20.8. Example

Examples are being processed to comply with Jakarta EE standards.

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