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YAVI (Yet Another ValIdation)

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YAVI (pronounced jɑ-vάɪ) is a lambda based type safe validation for Java.

Why YAVI?

YAVI sounds as same as a Japanese slang "YABAI" that means awesome or awful depending on the context.

The concepts are

  • No more reflection!
  • No more (runtime) annotation!
  • No more Java Beans!
  • Zero dependency!

If you are not a fan of Bean Validation, YAVI will be an awesome alternative.

For the migration from Bean Validation, refer the doc.

Usage

Add the following dependency in your pom.xml

<dependency>
    <groupId>am.ik.yavi</groupId>
    <artifactId>yavi</artifactId>
    <version>0.4.0</version>
</dependency>

If you want to try a snapshot version, add the following repository:

<repository>
    <id>sonatype-snapshots</id>
    <name>Sonatype Snapshots</name>
    <url>https://oss.sonatype.org/content/repositories/snapshots</url>
    <snapshots>
        <enabled>true</enabled>
    </snapshots>
</repository>

Example

Simple

Validator<User> validator = ValidatorBuilder.<User> of() // or ValidatorBuilder.of(User.class)
    .constraint(User::getName, "name", c -> c.notNull() //
        .lessThanOrEqual(20)) //
    .constraint(User::getEmail, "email", c -> c.notNull() //
        .greaterThanOrEqual(5) //
        .lessThanOrEqual(50) //
        .email()) //
    .constraint(User::getAge, "age", c -> c.notNull() //
        .greaterThanOrEqual(0) //
        .lessThanOrEqual(200))
    .build();

ConstraintViolations violations = validator.validate(user);
violations.isValid(); // true or false
violations.forEach(x -> System.out.println(x.message()));

sample code

In order to avoid ambiguous type inferences, you can use explicit _<type> method per type instead of constraint as follows:

// Needs YAVI 0.3.0+

Validator<User> validator = ValidatorBuilder.<User> of() // or ValidatorBuilder.of(User.class)
    ._string(User::getName, "name", c -> c.notNull() //
        .lessThanOrEqual(20)) //
    ._string(User::getEmail, "email", c -> c.notNull() //
        .greaterThanOrEqual(5) //
        .lessThanOrEqual(50) //
        .email()) //
    ._integer(User::getAge, "age", c -> c.notNull() //
        .greaterThanOrEqual(0) //
        .lessThanOrEqual(200))
    .build();

Does specifying "fieldName"s look redundant?

If you want to write as following, try Annotation Processor.

// Needs YAVI 0.4.0+

Validator<User> validator = ValidatorBuilder.<User> of()
    .constraint(_UserMeta.NAME, c -> c.notNull()
        .lessThanOrEqual(20))
    .constraint(_UserMeta.EMAIL, c -> c.notNull()
        .greaterThanOrEqual(5)
        .lessThanOrEqual(50)
        .email())
    .constraint(_UserMeta.AGE, c -> c.notNull()
        .greaterThanOrEqual(0)
        .lessThanOrEqual(200))
    .build();

If you are using Kotlin, you can write a bit shorter using konstraint method instead of constraint

val validator: Validator<User> = ValidatorBuilder.of<User>()
    .konstraint(User::name) {
        notNull() //
            .lessThanOrEqual(20)
    } //
    .konstraint(User::email) {
        notNull() //
            .greaterThanOrEqual(5) //
            .lessThanOrEqual(50) //
            .email()
    } //
    .konstraint(User::age) {
        notNull() //
            .greaterThanOrEqual(0) //
            .lessThanOrEqual(200)
    }
    .build()

Nested

Validator<Country> countryValidator = ValidatorBuilder.<Country> of() //
    .nest(Country::getName, "name", c -> c.notBlank() //
        .lessThanOrEqual(20))
    .build();
Validator<City> cityValidator = ValidatorBuilder.<City> of() //
    .nest(City::getName, "name", c -> c.notBlank() //
        .lessThanOrEqual(100))
    .build();

Validator<Address> validator = ValidatorBuilder.<Address> of() //
    .nest(Address::getCountry, "country", countryValidator) //
    .nest(Address::getCity, "city", cityValidator)
    .build();

sample code

or

Validator<Address> validator = ValidatorBuilder.<Address> of() //
      .nest(Address::getCountry, "country", //
            b -> b.constraint(Country::getName, "name", c -> c.notBlank() //
                                    .lessThanOrEqual(20))) //
      .nest(Address::getCity, "city", //
            b -> b.constraint(City::getName, "name", c -> c.notBlank() //
                                    .lessThanOrEqual(100))) //
      .build();

sample code

Does specifying "fieldName"s look redundant?

If you want to write as following, try Annotation Processor.

Validator<Address> validator = ValidatorBuilder.<Address> of()
    .nest(_AddressMeta.COUNTRY, countryValidator)
    .nest(_AddressMeta.CITY, cityValidator)
    .build();

// or

Validator<Address> validator = ValidatorBuilder.<Address> of()
      .nest(_AddressMeta.COUNTRY,
            b -> b.constraint(_Address_CountryMeta.NAME, c -> c.notBlank()
                                    .lessThanOrEqual(20)))
      .nest(_AddressMeta.CITY,
            b -> b.constraint(_Address_CityMeta.NAME, c -> c.notBlank()
                                    .lessThanOrEqual(100)))
      .build();

sample code

Elements in a List / Map / Array

Overriding violation messages

Validator<User> validator = ValidatorBuilder.<User> of() //
    .constraint(User::getName, "name", c -> c.notNull().message("name is required!") //
        .greaterThanOrEqual(1).message("name is too small!") //
        .lessThanOrEqual(20).message("name is too large!")) //
    .build()

Custom

public enum IsbnConstraint implements CustomConstraint<String> {
    SINGLETON;

    @Override
    public boolean test(String s) {
        return ISBNValidator.isISBN13(s);
    }

    @Override
    public String messageKey() {
        return "custom.isbn13";
    }

    @Override
    public String defaultMessageFormat() {
        return "\"{0}\" must be ISBN13 format";
    }
}
Validator<Book> book = ValidatorBuilder.<Book> of() //
    .constraint(Book::getTitle, "title", c -> c.notBlank() //
        .lessThanOrEqual(64)) //
    .constraint(Book::getIsbn, "isbn", c -> c.notBlank()//
        .predicate(IsbnConstraint.SINGLETON))
    .build(); //

sample code

Multi-fields validation

Validator<Range> validator = ValidatorBuilder.<Range> of() //
    .constraint(range::getFrom, "from", c -> c.greaterThan(0)) //
    .constraint(range::getTo, "to", c -> c.greaterThan(0)) //
    .constraintOnTarget(range -> range.to > range.from, "to", "to.isGreaterThanFrom", "\"to\" must be greater than \"from\".") //
    .build();

Either API

Either<ConstraintViolations, User> either = validator.validateToEither(user);

Optional<ConstraintViolations> violations = either.left();
Optional<User> user = either.right();

HttpStatus status = either.fold(v -> HttpStatus.BAD_REQUEST, u -> HttpStatus.OK);

Either API

Conditional Constraint

You can impose a condition on constraints with ConstraintCondition interface:

Validator<User> validator = ValidatorBuilder.of(User.class) //
    .constraintOnCondition((user, constraintGroup) -> !user.getName().isEmpty(), //
        b -> b.constraint(User::getEmail, "email",
            c -> c.email().notEmpty())) // <- this constraint on email is active only when name is not empty
    .build();

You can group the constraint as a part of ConstraintCondition with ConstraintGroup aas well:

enum Group implements ConstraintGroup {
    CREATE, UPDATE, DELETE
}

Validator<User> validator = ValidatorBuilder.of(User.class) //
    .constraintOnCondition(Group.UPDATE.toCondition(), //
        b -> b.constraint(User::getEmail, "email", c -> c.email().notEmpty()))
    .build();

The group to validate is specified in validate method:

validator.validate(user, Group.UPDATE);

You can also use a shortcut constraintOnGroup method

Validator<User> validator = ValidatorBuilder.of(User.class) //
    .constraintOnGroup(Group.UPDATE, //
        b -> b.constraint(User::getEmail, "email", c -> c.email().notEmpty()))
    .build();

Note that all constraints without conditions will be validated for any constraint group.

Arguments Validator

Since YAVI 0.3.0, you can validate arguments of a constructor or factory method "before" creating an object using it.

Validating Constructor Arguments

You can get the object only if the arguments passe the validation. Up to 16 arguments are supported.

Person person = ArgumentsValidatorBuilder
    .of(Person::new)
    .builder(b -> b
        ._string(Arguments1::arg1, "firstName",
            c -> c.greaterThanOrEqual(1).lessThanOrEqual(50))
        ._string(Arguments2::arg2, "lastName",
            c -> c.greaterThanOrEqual(1).lessThanOrEqual(50))
        ._integer(Arguments3::arg3, "age",
            c -> c.greaterThanOrEqual(20).lessThanOrEqual(99)))
    .build()
    .validated("John", "Doe", 35);

You can also get the result as Either.

Either<ConstraintViolations, Person> either  = ArgumentsValidatorBuilder
    .of(Person::new)
    .builder(b -> b
        ._string(Arguments1::arg1, "firstName",
            c -> c.greaterThanOrEqual(1).lessThanOrEqual(50))
        ._string(Arguments2::arg2, "lastName",
            c -> c.greaterThanOrEqual(1).lessThanOrEqual(50))
        ._integer(Arguments3::arg3, "age",
            c -> c.greaterThanOrEqual(20).lessThanOrEqual(99)))
    .build()
    .validateArgs("John", "Doe", 35);

Kotlin version

val person = ArgumentsValidatorBuilder
    .of(::Person)
    .builder { b ->
        b._string({ it.arg1() }, "firstName") {
            it.greaterThanOrEqual(1).lessThanOrEqual(50)
        }._string({ it.arg2() }, "lastName") {
            it.greaterThanOrEqual(1).lessThanOrEqual(50)
        }._integer({ it.arg3() }, "age") {
            it.greaterThanOrEqual(20).lessThanOrEqual(99)
        }
    }
    .build()
    .validated("John", "Doe", 20)

If you want to validate arguments in the constructor, use validateAndThrowIfInvalid so that the constructor cannot be called recursively in the constructor.

static final Arguments3Validator<String, String, Integer, Person> validator = ArgumentsValidatorBuilder
    .of(Person::new)
    .builder(b -> b
        ._string(Arguments1::arg1, "firstName",
            c -> c.greaterThanOrEqual(1).lessThanOrEqual(50))
        ._string(Arguments2::arg2, "lastName",
            c -> c.greaterThanOrEqual(1).lessThanOrEqual(50))
        ._integer(Arguments3::arg3, "age",
            c -> c.greaterThanOrEqual(20).lessThanOrEqual(99)))
    .build();

public Perrson(String firstName, String lastName, int age) {
    validator.validateAndThrowIfInvalid(firstName, lastName, age);
    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;
}

Does specifying "fieldName"s look redundant? Try Annotation Processor.

Validating Method Arguments

Arguments Validator can be used for validating method arguments as well.

// From https://beanvalidation.org/
public class UserService {

  public User createUser(/* @Email */ String email,
                         /* @NotNull */ String name) {
    ...
  }
}
static final Arguments3Validator<UserService, String, String, User> validator = ArgumentsValidatorBuilder
        .of(UserService::createUser) //
        .builder(b -> b //
                ._object(Arguments1::arg1, "userService", c -> c.notNull())
                ._string(Arguments2::arg2, "email", c -> c.email())
                ._string(Arguments3::arg3, "name", c -> c.notNull())) //
        .build();

UserService userService = new UserService();
User user = validator.validated(userService, "[email protected]", "John Doe");

Note that void cannot be used as return type while java.lang.Void is available.

Does specifying "fieldName"s look redundant? Try Annotation Processor.

(Experimental) Emoji support

By default, some Emojis are not counted as you expect.

For example,

Validator<Message> validator = ValidatorBuilder.<Message> of() //
      .constraint(Message::getText, "text", c -> c.notBlank() //
          .lessThanOrEqual(3)) //
      .build(); //
validator.validate(new Message("I❤️☕️")).isValid(); // false

If you want to count as you see (3, in this case), use emoji().

Validator<Message> validator = ValidatorBuilder.<Message> of() //
      .constraint(Message::getText, "text", c -> c.notBlank() //
          .emoji().lessThanOrEqual(3)) //
      .build(); //
validator.validate(new Message("I❤️☕️")).isValid(); // true

For the safety (such as storing into a database), you can also check the size as byte arrays

Validator<Message> validator = ValidatorBuilder.<Message> of() //
      .constraint(Message::getText, "text", c -> c.notBlank() //
          .emoji().lessThanOrEqual(3)
          .asByteArray().lessThanOrEqual(16)) //
      .build(); //
validator.validate(new Message("I❤️☕️")).isValid(); // true
validator.validate(new Message("❤️️❤️️❤️️")).isValid(); // false

Example with Spring WebFlux.fn

YAVI will be a great fit for Spring WebFlux.fn

static RouterFunction<ServerResponse> routes() {
  return route()
      .POST("/", req -> req.bodyToMono(User.class) //
        .flatMap(body -> validator.validateToEither(body) //
          .leftMap(violations -> {
            Map<String, Object> error = new LinkedHashMap<>();
            error.put("message", "Invalid request body");
            error.put("details", violations.details());
            return error;
          })
          .fold(error -> badRequest().bodyValue(error), //
              user -> ok().bodyValue(user))))
      .build();
}

sample app

Example with Spring MVC

@PostMapping("users")
public String createUser(Model model, UserForm userForm, BindingResult bindingResult) {
  ConstraintViolations violations = validator.validate(userForm);
  if (!violations.isValid()) {
    violations.apply(BindingResult::rejectValue);
    return "userForm";
  }
  // ...
  return "redirect:/";
}

or

@PostMapping("users")
public String createUser(Model model, UserForm userForm, BindingResult bindingResult) {
  return validator.validateToEither(userForm)
    .fold(violations -> {
      violations.apply(BindingResult::rejectValue);
      return "userForm";
    }, form -> {
      // ...
      return "redirect:/";
    });
}

sample app

Required

  • Java 8+

License

Licensed under the Apache License, Version 2.0.