YAVI

YAVI (Yet Another ValIdation)

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

Why YAVI?

YAVI sounds as same as a Japanese slang "YABAI (ヤバイ)" that means awesome or awful depending on the context (like "Crazy"). If you use YAVI, you will surely understand that it means the former.

The concepts are

• No reflection!
• No (runtime) annotation!
• Not only Java Beans!
• Only one dependency (JSpecify)

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

YAVI has the following features:

• Type-safe constraints, unsupported constraints cannot be applied to the wrong type
• Fluent and intuitive API
• Constraints on any object. Java Beans, Records, Protocol Buffers, Immutables and anything else.
• Lots of powerful built-in constraints
• Easy custom constraints
• Validation for groups, conditional validation
• Validation for arguments before creating an object
• Support for API and combination of validation results and validators that incorporate the concept of functional programming

See the reference documentation for details.

Presentations

• 2021-07-01 YAVIの紹介 (Japanese) [Deck] [Recording]

Getting Started

This content is derived from https://hibernate.org/validator/documentation/getting-started/

Welcome to YAVI.

The following paragraphs will guide you through the initial steps required to integrate YAVI into your application.

Prerequisites

• Java Runtime >= 21 for YAVI 0.18 and later, >= 8 for earlier versions
• Apache Maven

Project set up

This guide uses the API of YAVI 0.18.0, which is not released yet. In order to use its snapshot within a Maven project, add the following dependency and repository to your pom.xml:

<dependency>
    <groupId>am.ik.yavi</groupId>
    <artifactId>yavi</artifactId>
    <version>0.18.0-SNAPSHOT</version>
</dependency>

<repositories>
    <repository>
        <id>central-snapshots</id>
        <url>https://central.sonatype.com/repository/maven-snapshots/</url>
        <releases>
            <enabled>false</enabled>
        </releases>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </repository>
</repositories>

The latest release is 0.17.3; see the reference documentation for its API.

This tutorial uses JUnit and AssertJ. Add the following dependencies as needed:

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-api</artifactId>
    <version>6.1.3</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.assertj</groupId>
    <artifactId>assertj-core</artifactId>
    <version>3.27.7</version>
    <scope>test</scope>
</dependency>

Choosing a style

YAVI validates in two styles. Choose by what you have in hand when validation starts:

You have	You want	Use
Input that is not an object yet: a Map, a parsed JSON document, request parameters	To validate it and then create the object, so that an invalid object never exists	Yavi.schema() ... fromMap(...)
An object that is already created, as with Bean Validation	The "classic" style: to check the object and get its violations	ValidatorBuilder

Validating an input and creating an object

Yavi.schema() describes the properties of an input, and fromMap ends it with a validator that reads them from a Map<String, Object> by their names, checks their types and gives them to a constructor. The object is created only when every property is valid.

Create src/main/java/com/example/Car.java and write the following code.

package com.example;

import am.ik.yavi.input.ObjectInputValidator;
import am.ik.yavi.validator.Yavi;

public record Car(String manufacturer, String licensePlate, Integer seatCount) {
    public static final ObjectInputValidator<Car> validator = Yavi.schema()
            ._string("manufacturer")
            ._string("licensePlate", c -> c.greaterThanOrEqual(2).lessThanOrEqual(14))
            ._integer("seatCount", c -> c.greaterThanOrEqual(2))
            .fromMap(Car::new);
}

Each method of the schema declares a property with its type, its name and its constraints:

• manufacturer must be a string
• licensePlate must be a string that is between 2 and 14 characters long
• seatCount must be an integer that is at least 2

A property is required: an absent key is reported with object.required ("manufacturer" is required) and null with object.notNull ("manufacturer" must not be null), so notNull() need not be written and the constructor is never given null. A property that may be null says so with nullable() or optional(), as described below.

To perform a validation, give a map to the validator. To demonstrate this, let’s have a look at a simple unit test:

Create src/test/java/com/example/CarTest.java and write the following code.

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