validations for Kotlin

kvalidation - Validation library for Kotlin

Installation

Add to gradle.build.kts:

repositories {
    maven {
        url = uri("https://maven.pkg.github.com/hwolf/validation")
    }
}

dependencies {
    implementation("hwolf.kvalidation:kvalidation-core:0.1.0")
    implementation("hwolf.kvalidation:kvalidation-common:0.1.0")
}

Usage

Suppose you have a class like this:

data class UserProfile(
    val name: String,
    val age: Int?,
    val password: String?,
    val confirmPassword: String?,
    val email: String?
)

Using the type-safe DSL you can write a validator:

val userProfileValidator = validator<UserProfile> {
    UserProfile::name {
        isNotBlank()
        hasLength(6, 20)
    }
    UserProfile::age required {
        isGreaterOrEqual(18)
    }
    UserProfile::password required {
        hasLength(8, 40)
    }
    UserProfile::confirmPassword required {
        isEqual(UserProfile::password)
    }
    UserProfile::email ifPresent {
        isEmail()
    }
}

and apply it to your data

val invalidUserProfile = UserProfile(
        name = "Mr. X",
        age = 16,
        password = "geheim",
        confirmPassword = "anders",
        email = "keine Mail")
val result = userProfileValidator.validate(invalidUserProfile)

Creating a custom validation

It's possible to create custom validations:

Define the constraint

To create a custom constraint, it's necessary to implement the interface hwolf.kvalidation.Constraint, which has these properties:

• messageKey: specifies the name of the key for interpolating messages, the default value is the qualified class name plus message suffix.
• parameters: specifies a Map<String, Amy?> containing the parameters to be replaced in the message, the default values are all class properties, obtained through reflection.

For example:

data class MinLength<T>(val min: T) : Constraint

Create the extension function

The validation logic must be within an extension function of hwolf.kvalidation.ConstraintBuilder<T>.validate.validate(constraint: Constraint, test: (V) -> Boolean), where

• T represents the type of the property
• constraint the constraint
• test a validation function

For example:

fun <T> ValidationBuilder<T, String>.hasMinLength(min: Int) =
    validate(MinLength(min)) { v, _ ->
        v.length >= min
    }