Faker Configuration

ToC


Default Configuration

Faker can be configured through the FakerConfig class, either by passing an instance of FakerConfig directly, or

If no FakerConfig instance is passed to Faker constructor and configuration is not set through the faker builder DSL, then default configuration will be used:

  • locale == "en"
  • random is seeded with a pseudo-randomly generated number.
  • uniqueGeneratorRetryLimit is set to 100
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Deterministic Random

Faker supports seeding of it's PRNG (pseudo-random number generator) through FakerConfig to provide deterministic output of repeated function invocations.

val config = fakerConfig {
    random = Random(42)
}
val faker = Faker(config)
val city1 = faker.address.city()
val name1 = faker.name.name()

val otherConfig = fakerConfig {
    random = Random(42)
}
val otherFaker = Faker(otherConfig)
val city2 = otherFaker.address.city()
val name2 = otherFaker.name.name()

assertEquals(city1, city2)
assertEquals(name1, name2)


FakerConfig.Builder configBuilder = FakerConfig.builder();

Faker faker = new Faker(configBuilder.withRandom(new Random(42)).build());
String city1 = faker.getAddress().city();
String name1 = faker.getName().name();

Faker otherFaker = new Faker(configBuilder.withRandom(new Random(42)).build());
String city2 = otherFaker.getAddress().city();
String name2 = otherFaker.getName().name();

assertEquals(city1, city2);
assertEquals(name1, name2);


Alternatively a randomSeed property can be used instead of passing an instance of java.util.Random:

val config = fakerConfig {
    randomSeed = 42
}
val faker = Faker(config)


FakerConfig config = FakerConfig.builder()
    .withRandomSeed(42)
    .build();
Faker faker = new Faker(config);
info

randomSeed config property has precedence over random property, and the latter will be ignored if randomSeed is specified.

val config = fakerConfig {
    random = Random(123)
    randomSeed = 42
}
val faker = Faker(config)
val city1 = faker.address.city()

val otherConfig = fakerConfig {
    random = Random(123)
    randomSeed = 42
}
val otherFaker = Faker(otherConfig)
val city2 = otherFaker.address.city()

assertEquals(city1, city2)


FakerConfig config = FakerConfig.builder()
    .withRandom(new Random(123))
    .withRandomSeed(42)
    .build();
Faker faker = new Faker(config);
String city1 = faker.getAddress().city();

FakerConfig otherConfig = FakerConfig.builder()
    .withRandom(new Random(42))
    .build();
Faker otherFaker = new Faker(otherConfig);
String city2 = otherFaker.getAddress().city();

assertEquals(city1, city2);
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Locale

By default Faker uses en_US-localized dict files to generate data:

val faker = Faker()
assertEquals(faker.address.defaultCountry(), "United States of America")


When needed, Faker can be configured to use a custom localized dictionary file instead:

val config = fakerConfig {
    locale = "nb-NO"
}
val faker = Faker(config)
assertEquals(faker.address.defaultCountry(), "Norge")


FakerConfig config = FakerConfig.builder()
    .withLocale("nb-NO")
    .build();
Faker faker = new Faker(config);
assertEquals(faker.getAddress().defaultCountry(), "Norge");
info

The locale configuration property should be set following the .yml dict file name, that is a - should be used as a delimiter between "language" and "country" values instead of _, i.e. nb-NO instead of nb_NO.



Using a non-default locale will replace the values in some of the providers with the values from localized dictionary.

val config = fakerConfig { locale = "es" }
val faker = Faker(config)
faker.address.city() // => Barcelona


info

Note that if the localized dictionary file does not contain a category (or a parameter in a category) that is present in the default locale, then non-localized (`en`) value will be generated instead. 

val faker = Faker() // uses default 'en' locale
faker.gameOfThrones.cities() // => Braavos

val config = fakerConfig {
    locale = "nb-NO"
}
val localizedFaker = Faker(config)
// 'game_of_thrones' category is not localized for `nb-NO` locale
// and non-localized value is returned instead
localizedFaker.gameOfThrones.cities() // => Braavos


A list of all locales, and their corresponding dictionary files, can be found on the Available Locales page.

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Random Class Instance

RandomClassInstance can also be configured both from the FakerConfig level.

info

This configuration takes the least precedence and will be overridden by config set on the `faker.randomProvider` level or on the `randomClassInstance` function level. See [Random Class Instance Configuration](https://serpro69.github.io/kotlin-faker/wiki/extras#random-class-instance-configuration) for more details.

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