Configuration

Module is responsible for mapping the values of configuration files to classes in Kora and then using them for application settings.

HOCON¶

Support for HOCON is implemented with Typesafe Config. HOCON is a JSON-based config file format. The format is less strict than JSON and has a slightly different syntax.

services {
    foo {
      bar = "SomeValue" //(1)!
      baz = 10 //(2)!
      propRequired = ${REQUIRED_ENV_VALUE} //(3)!
      propOptional = ${?OPTIONAL_ENV_VALUE} //(4)!
      propDefault = 10
      propDefault = ${?NON_DEFAULT_ENV_VALUE} //(5)!
      propReference = ${services.foo.bar}Other${services.foo.baz} //(6)!
      propArray = ["v1", "v2"] //(7)!
      propArrayAsString = "v1, v2" //(8)!
      propMap { //(9)!
          "k1" = "v1"
          "k2" = "v2"
      }
    }
}

String configuration value
Numeric configuration value
Mandatory configuration value that is substituted from the REQUIRED_ENV_VALUE environment variable.
Optional configuration value which is substituted from the OPTIONAL_ENV_VALUE environment variable, if no such variable is found, the configuration value will be omitted. 5.
Configuration value with default value, the default value is specified in propDefault = 10 and if NON_DEFAULT_ENV_VALUE environment variable is found, its value will replace the default value.
Configuration value assembled from substitutions of other parts of the configuration and the Other value between the
String list configuration value, the value is set as an array of strings or can also be set as a string with values separated by commas
String list configuration value, the value is set as a string with values separated by commas or can also be set as an array of strings
Configuration value as a dictionary key and value

Configuration representation in code:

Java Kotlin

@ConfigSource("services.foo")
public interface FooConfig {

    String bar();

    Integer baz();

    String propRequired();

    @Nullable
    String propOptional();

    Integer propDefault();

    String propReference();

    List<String> propArray();

    List<String> propArrayAsString();

    Map<String, String> propMap();
}

@ConfigSource("services.foo")
interface FooConfig {

    fun bar(): String

    fun baz(): Int

    fun propRequired(): String

    fun propOptional(): String?

    fun propDefault(): Int

    fun propReference(): String

    fun propArray(): List<String>

    fun propArrayAsString(): List<String>

    fun propMap(): Map<String, String>
}

Dependency¶

Java Kotlin

Dependency build.gradle:

annotationProcessor "ru.tinkoff.kora:annotation-processors"
implementation "ru.tinkoff.kora:config-hocon"

Module:

@KoraApp
public interface Application extends HoconConfigModule { }

Dependency build.gradle.kts:

ksp("ru.tinkoff.kora:symbol-processors")
implementation("ru.tinkoff.kora:config-hocon")

Module:

@KoraApp
interface Application : HoconConfigModule

File¶

By default, the configuration files reference.conf and application.conf are expected.

First, all reference.conf files are merged, second, the application.conf file is overlaid on the unresolved reference.conf file, the result is calculated and checked that all variable values are available.

It is assumed that the application configuration is in application.conf and the library configurations are in reference.conf.

Prioritize reading the application.conf configuration file:

Use the file from config.resource if specified (file from resources directory)
Use the file from config.file if specified (file from the file system)
Use the application.conf file if available (file from resources directory)
Use an empty configuration file if none of the above is present

YAML¶

Support for YAML is implemented using SnakeYAML.

services:
    foo:
        bar: "SomeValue" #(1)!
        baz: 10 #(2)!
        propRequired: ${REQUIRED_ENV_VALUE} #(3)!
        propOptional: ${?OPTIONAL_ENV_VALUE} #(4)!
        propDefault: ${?NON_DEFAULT_ENV_VALUE:10} #(5)!
        propReference: ${services.foo.bar}Other${services.foo.baz} #(6)!
        propArray: ["v1", "v2"] #(7)!
        propArrayAsString: "v1, v2" #(8)!
        propMap: #(9)!
            k1: "v1"
            k2: "v2"

String configuration value
Numeric configuration value
Mandatory configuration value that is substituted from the REQUIRED_ENV_VALUE environment variable.
Optional configuration value which is substituted from the OPTIONAL_ENV_VALUE environment variable, if no such variable is found, the configuration value will be omitted. 5.
Configuration value with default value, the default value is specified as 10 and if NON_DEFAULT_ENV_VALUE environment variable is found, its value will replace the default value.
Configuration value assembled from substitutions of other parts of the configuration and the Other value between the
String list configuration value, the value is set as an array of strings or can also be set as a string with values separated by commas
String list configuration value, the value is set as a string with values separated by commas or can also be set as an array of strings
Configuration value as a dictionary key and value

Configuration representation in code:

Java Kotlin

@ConfigSource("services.foo")
public interface FooConfig {

    String bar();

    Integer baz();

    String propRequired();

    @Nullable
    String propOptional();

    Integer propDefault();

    String propReference();

    List<String> propArray();

    List<String> propArrayAsString();

    Map<String, String> propMap();
}

@ConfigSource("services.foo")
interface FooConfig {

    fun bar(): String

    fun baz(): Int

    fun propRequired(): String

    fun propOptional(): String?

    fun propDefault(): Int

    fun propReference(): String

    fun propArray(): List<String>

    fun propArrayAsString(): List<String>

    fun propMap(): Map<String, String>
}

Dependency¶

Java Kotlin

Dependency build.gradle:

annotationProcessor "ru.tinkoff.kora:annotation-processors"
implementation "ru.tinkoff.kora:config-yaml"

Module:

@KoraApp
public interface Application extends YamlConfigModule { }

Dependency build.gradle.kts:

ksp("ru.tinkoff.kora:symbol-processors")
implementation("ru.tinkoff.kora:config-yaml")

Module:

@KoraApp
interface Application : YamlConfigModule

File¶

By default, the reference.yaml and application.yaml configuration files are expected.

First, all reference.yaml files are merged, second, the application.yaml file is overlaid on an unresolved reference.yaml file, the result is calculated and it is checked that all variable values are available.

It is assumed that the application configuration is in the application.yaml file and the library configurations are in reference.yaml.

Prioritize reading the application.yaml configuration file:

Use the file from config.resource if specified (file from resources directory)
Use the file from config.file if specified (file from the file system)
Use the application.yaml file if available (file from resources directory)
Use an empty configuration file if none of the above is present

Custom configuration¶

A custom configuration provides a mapping of the configuration file to a user interface. Such a user interface can later be injected as a dependency along with other components.

Application config¶

In order to simplify the creation of custom configurations, the @ConfigSource annotation should be used:

Java Kotlin

@ConfigSource("services.foo")
public interface FooServiceConfig {

    String bar();

    int baz();
}

@ConfigSource("services.foo")
interface FooServiceConfig {

    fun bar(): String

    fun baz(): Int
}

This code sample will add an instance of the FooServiceConfig class to the dependency container, which when created will expect the following kind of configuration:

Hocon YAML

services {
  foo {
    bar = "SomeValue"
    baz = 10
  }
}

services:
  foo:
    bar: "SomeValue"
    baz: 10

After that, the FooServiceConfig class can already be used as a dependency in other classes:

Java Kotlin

@Component
public final class FooService {

    private final FooServiceConfig config;

    public FooService(FooServiceConfig config) {
        this.config = config;
    }
}

@Component
class FooService(val config: FooServiceConfig)

Library config¶

In order to create custom configurations within custom libraries, use the @ConfigValueExtractor annotation which will create rules for processing a configuration file into an instance of a configuration class.

Let's consider an example when there is such a configuration class:

Java Kotlin

@ConfigValueExtractor
public interface FooLibraryConfig {

    String bar();

    int baz();
}

@ConfigValueExtractor
interface FooLibraryConfig {

    fun bar(): String

    fun baz(): Int
}

In order for the library to provide configuration, you need to implement the factory in a module:

Java Kotlin

public interface FooLibraryModule {

    default FooLibraryConfig config(Config config, ConfigValueExtractor<FooLibraryConfig> extractor) {
        return extractor.extract(config.get("library.foo"));
    }
}

interface FooLibraryModule {

    fun config(config: Config, extractor: ConfigValueExtractor<FooLibraryConfig>): FooLibraryConfig {
        return extractor.extract(config["library.foo"])!!
    }
}

The factory will expect a configuration of the following kind:

Hocon YAML

library {
  foo {
    bar = "SomeValue"
    baz = 10
  }
}

library:
  foo:
    bar: "SomeValue"
    baz: 10

Then by connecting the FooLibraryModule module in the application, the FooServiceConfig config can be used as a dependency in other classes.

Required values¶

By default, all values declared in the config are considered required (NotNull) and must be present in the configuration file.

Optional values¶

If you need to specify a value from the configuration file as optional, you can use this format:

Java Kotlin

It is suggested to use the @Nullable annotation over the method signature:

@ConfigSource("services.foo")
public interface FooServiceConfig {

    @Nullable//(1)!
    String bar();

    int baz();
}

Any @Nullable annotation will do, such as javax.annotation.Nullable / jakarta.annotation.Nullable / org.jetbrains.annotations.Nullable / etc.

It is expected to use the Kotlin Nullability syntax and mark such a parameter as Nullable:

@ConfigSource("services.foo")
interface FooServiceConfig {

    fun bar(): String?

    fun baz(): Int
}

Default values¶

If there is a need to use default values in a class, you can use this format:

Java Kotlin

@ConfigSource("services.foo")
public interface FooServiceConfig {

    String bar();

    default int baz() {
        return 42;
    }
}

@ConfigSource("services.foo")
interface FooServiceConfig {

    fun bar(): String

    fun baz(): Int {
        return 42
    }
}

Injecting configuration¶

You can inject the base class ru.tinkoff.kora.config.common.Config which provides a common abstraction over the configuration file mapping. The resulting configuration mapping consists of several layers that represent:

Environment variables
System variables
Configuration file

Environment variables¶

In case you want to embed the configuration only environment variables, you can use the @Environment annotation as a tag for the configuration class:

Java Kotlin

@Component
public final class FooService {

    private final Config config;

    public FooService(@Environment Config config) {
        this.config = config;
    }
}

@Component
class FooService(@Environment val config: Config)

System variables¶

In case you want to inject a configuration of only system variables, then you can use the @SystemProperties annotation as a tag for the configuration class:

Java Kotlin

@Component
public final class FooService {

    private final Config config;

    public FooService(@SystemProperties Config config) {
        this.config = config;
    }
}

@Component
class FooService(@SystemProperties val config: Config)

Configuration file¶

In case you want to inject a complete application configuration that consists only of a configuration file, you can use the @ApplicationConfig annotation as a tag for the configuration class:

Java Kotlin

@Component
public final class FooService {

    private final Config config;

    public FooService(@ApplicationConfig Config config) {
        this.config = config;
    }
}

@Component
class FooService(@ApplicationConfig val config: Config)

Resulting configuration¶

If you want to inject a complete application configuration that consists of a configuration file, environment variables and system variables, you simply inject the configuration class without the tag:

Java Kotlin

@Component
public final class FooService {

    private final Config config;

    public FooService(Config config) {
        this.config = config;
    }
}

@Component
class FooService(val config: Config)

Recommendations¶

Tip

We do not recommend using ru.tinkoff.kora.config.common.Config directly as a dependency in components, because when you update the configuration it will cause all graph components that use it to be updated, it is recommended to always create custom user configuration interfaces.

Config Watcher¶

By default, Kora has a configuration file watcher that updates the contents of the configuration file, which causes the dependency graph for the affected components to be updated if the configuration file is changed.

You can disable the watcher by using:

Environment variable KORA_CONFIG_WATCHER_ENABLED.
System property kora.config.watcher.enabled.

Supported types¶

Configuration Extractors provide an extensive list of supported types that covers most of what you might need to specify in custom configurations, or you can extend the behavior with your custom ConfigValueExtractor<T> component.

List of supported types

boolean / Boolean
short / Short
int / Integer
long / Long
double / Double
float / Float
double[]
String
BigInteger
BigDecimal
Period
Duration
Size
Properties
Pattern
UUID
Properties
LocalDate
LocalTime
LocalDateTime
OffsetTime
OffsetDateTime
Enum (any custom ENUM type)
List<T> (where T is any of the above listed types)
Set<T> (where T is any of the above types)
Map<String, T> (where T is any of the above types)
Either<A, B> (where A and B are any of the above types)