Configuring Faker¶

Default Configuration¶

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

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 with the following values:

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

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

Faker otherFaker = new Faker(configBuilder.withRandom(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);

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

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

assertEquals(city1, city2);

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");

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

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

Random Class Instance¶

RandomClassInstance can also be configured from the FakerConfig.