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Hibernate Validator 5.2.0.Alpha1 with Java 8 support and a 5.1 maintenance release

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After some time in the making, we are happy to announce the first Hibernate Validator release of the 5.2 series - 5.2.0.Alpha1. This release focuses mainly on Java 8 support, but we will get to this in a bit.

First a big thank you to Khalid Alqinyah who, as part of a Google Summer of Code project, implemented many of these new features.

So what's in it for you?

Java 8 support

Note: Java 8 is not a requirement for Hibernate Validator 5.2. Hibernate Validator is still backward compatible with Java 6. Java 8 specific features are only enabled when a Java 8 runtime is detected.

First off, the Java 8 date/time data types (JSR 310) are supported and can be validated via @Past and @Future. Also Optional and JavaFX types are supported via an improved ValidatedValueUnwrapper. ValidatedValueUnwrapper was already introduced in Validator 5.1, but works now in a more transparent way. Upon validation all registered ValidatedValueUnwrapper instances are checked. If a handler supports the validated type its handleValidatedValue method is called, provided that there exists no matching ConstraintValidator for the wrapper itself. This is best explained with an example:

@Size(min = 3) // the @Size constraint can only apply to the string value which gets automatically validated
private Optional<String> firstName = Optional.of( "John" );

@NotNull
@UnwrapValidatedValue(false) // Use @UnwrapValidatedValue(false) to ensure the wrapper itself is validated
private Optional<String> lastName = Optional.of( "Doe" );
Another Java 8 related feature is the ability to use type annotations on Iterable instances. Something like this:
private List<@AcmeEmail String> emails;
Note that the example is not using Hibernate Validator's @Email. Neither Bean Validation's built-in constraints nor Hibernate Validator specific ones, can be used. The simple reason is that these constraints are missing java.lang.annotation.ElementType.TYPE_USE in their definition and it cannot be added in a backwards compatible way. At the moment we have not yet decided what to do. Should we make Java 8 a requirement for Validator 5.2 or should we somehow provide JVM specific artifacts? What do you think? Right now we want to keep the options open and see which path Bean Validation 1.2 and other Java EE 8 standards are taking. For now this feature is limited to custom constraints where you can add the required ElementType yourself.

Last but not least, in the Java 8 driven feature list, is ReflectionParameterNameProvider. This new ParameterNameProvider makes use of enhancements in the Java 8 reflection API and reports actual parameter names instead of the generic arg0, arg1, etc. A requirement for this provider to work is that the sources are compiled with the -parameters compiler option. Refer to the docs to see how to configure a custom ParameterNameProvider.

What else?

Here are a couple of more highlights from this release:

ConstraintDefinitionContributor and ServiceLoader for constraint definitions

The Bean Bean Validation specification allows to register new constraint definitions via XML mapping files. For example: 

<constraint-definition annotation="org.hibernate.validator.constraints.URL">
  <validated-by include-existing-validators="false">
    <value>org.hibernate.validator.constraintvalidators.RegexpURLValidator</value>
  </validated-by>
</constraint-definition>

We offer now two more ways of contributing constraint definitions. The first is programmatically via the ConstraintDefinitionContributor SPI. The above example would look like: 

HibernateValidatorConfiguration configuration = Validation
        .byProvider( HibernateValidator.class )
        .configure();

configuration.addConstraintDefinitionContributor(
        new ConstraintDefinitionContributor() {
                @Override
                public void collectConstraintDefinitions(ConstraintDefinitionBuilder builder) {
                        builder.constraint( URL.class )
                                .includeExistingValidators( false )
                                .validatedBy( RegexpURLValidator.class );
                }
        }
);

By the way, org.hibernate.validator.constraintvalidators.RegexpURLValidator is not a made up class. It is another new feature (HV-920) which allows to configure a regular expression based validator for the @URL constraint.

Back to constraint definition though. The second way to contribute constraint definitions is via the Java ServiceLoader mechanism. Just add META-INF/services/javax.validation.ConstraintValidator to your artifact listing the fully qualified classnames of your constraint validator classes (one per line). This mechanism works fine for adding constraint definitions for new types. You cannot as possible in XML or via the ConstraintDefinitionContributor disable default definitions.

ParameterMessageInterpolator

Hibernate Validator requires per default an implementation of the Unified EL to be available. For environments where you cannot or do not want to provide an EL implementation, we offer now a non EL based message interpolator - org.hibernate.validator.messageinterpolation.ParameterMessageInterpolator.

Warning: Constraint messages containing EL expressions will be returned un-interpolated!

These were just the highlights. In total a whopping 40 issues got resolved. Be one of the early adopters and get the Maven artifacts from the JBoss Maven repository (GAV org.hibernate:hibernate-validator:5.2.Alpha1) or the SourceForge distribution bundles.

Simultaneously with the 5.2 alpha release we published a 5.1 maintenance release. We accidentally broke Java 6 backwards compatibility in 5.1.2.Final by using Collections#emptyIterator(). This is corrected in 5.1.3.Final and Java 6 compatibility is restored.

The second bug fixed in 5.1.3.Final is HV-930 where constraints were not validated when the internal weak reference cache of Hibernate Validator got partly invalidated due to memory pressure.

The full 5.1.3.Final change log can be found here. Maven artifacts are on the JBoss Maven repository under the GAV org.hibernate:hibernate-validator:5.1.3.Final and distribution bundles are available on SourceForge.

If you are using a 5.1 version of Validator it is highly recommended to upgrade to 5.1.3.Final. Or why not giving the 5.2 Alpha version a go?

Feedback and questions are welcome via the Hibernate Validator forum or on stackoverflow using the hibernate-validator tag.

Enjoy!

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