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Mapping configuration to objects

With config mappings it is possible to group multiple configuration properties in a single interface that share the same prefix.

1. @ConfigMapping

A config mapping requires a public interface with minimal metadata configuration and annotated with the @io.smallrye.config.ConfigMapping annotation.

@ConfigMapping(prefix = "server")
public interface Server {
    String host();

    int port();
}

The Server interface is able to map configuration properties with the name server.host into the Server.host() method and server.port into Server.port() method. The configuration property name to look up is built from the prefix, and the method name with . (dot) as the separator.

If a mapping fails to match a configuration property a NoSuchElementException is thrown, unless the mapped element is an Optional.

1.1. Registration

When a Quarkus application starts, a config mapping can be registered twice. One time for STATIC INIT and a second time for RUNTIME INIT:

1.1.1. STATIC INIT

Quarkus starts some of its services during static initialization, and Config is usually one of the first things that is created. In certain situations it may not be possible to correctly initialize a config mapping. For instance, if the mapping requires values from a custom ConfigSource. For this reason, any config mapping requires the annotation @io.quarkus.runtime.configuration.StaticInitSafe to mark the mapping as safe to be used at this stage. Learn more about registration of a custom ConfigSource.

1.1.1.1. Example
@StaticInitSafe
@ConfigMapping(prefix = "server")
public interface Server {
    String host();

    int port();
}

1.1.2. RUNTIME INIT

The RUNTIME INIT stage happens after STATIC INIT. There are no restrictions at this stage, and any config mapping is added to the Config instance as expected.

1.2. Retrieval

A config mapping interface can be injected into any CDI aware bean:

class BusinessBean {
    @Inject
    Server server;

    public void businessMethod() {
        String host = server.host();
    }
}

In non-CDI contexts, use the API io.smallrye.config.SmallRyeConfig#getConfigMapping to retrieve the config mapping instance:

SmallRyeConfig config = ConfigProvider.getConfig().unwrap(SmallRyeConfig.class);
Server server = config.getConfigMapping(Server.class);

1.3. Nested groups

A nested mapping provides a way to subgroup other config properties:

@ConfigMapping(prefix = "server")
public interface Server {
    String host();

    int port();

    Log log();

    interface Log {
        boolean enabled();

        String suffix();

        boolean rotate();
    }
}
application.properties
server.host=localhost
server.port=8080
server.log.enabled=true
server.log.suffix=.log
server.log.rotate=false

The method name of a mapping group acts as sub-namespace to the configurations properties.

1.4. Overriding property names

1.4.1. @WithName

If a method name, or a property name do not match with each other, the @WithName annotation can override the method name mapping and use the name supplied in the annotation:

@ConfigMapping(prefix = "server")
public interface Server {
    @WithName("name")
    String host();

    int port();
}
application.properties
server.name=localhost
server.port=8080

1.4.2. @WithParentName

The @WithParentName annotation allows to configurations mapping to inherit its container name, simplifying the configuration property name required to match the mapping:

interface Server {
    @WithParentName
    ServerHostAndPort hostAndPort();

    @WithParentName
    ServerInfo info();
}

interface ServerHostAndPort {
    String host();

    int port();
}

interface ServerInfo {
    String name();
}
application.properties
server.host=localhost
server.port=8080
server.name=konoha

Without the @WithParentName the method name() requires the configuration property server.info.name. Because we use @WithParentName, the info() mapping will inherit the parent name from Server and name() maps to server.name instead.

1.4.3. NamingStrategy

Method names in camelCase map to kebab-case property names:

@ConfigMapping(prefix = "server")
public interface Server {
    String theHost();

    int thePort();
}
application.properties
server.the-host=localhost
server.the-port=8080

The mapping strategy can be adjusted by setting namingStrategy value in the @ConfigMapping annotation:

@ConfigMapping(prefix = "server", namingStrategy = ConfigMapping.NamingStrategy.VERBATIM)
public interface ServerVerbatimNamingStrategy {
    String theHost();

    int thePort();
}
application.properties
server.theHost=localhost
server.thePort=8080

The @ConfigMapping annotation support the following naming strategies:

  • KEBAB_CASE (default) - The method name is derived by replacing case changes with a dash to map the configuration property.

  • VERBATIM - The method name is used as is to map the configuration property.

  • SNAKE_CASE - The method name is derived by replacing case changes with an underscore to map the configuration property.

1.5. Conversions

A config mapping class support automatic conversions of all types available for conversion in Config:

@ConfigMapping
public interface SomeTypes {
    @WithName("int")
    int intPrimitive();

    @WithName("int")
    Integer intWrapper();

    @WithName("long")
    long longPrimitive();

    @WithName("long")
    Long longWrapper();

    @WithName("float")
    float floatPrimitive();

    @WithName("float")
    Float floatWrapper();

    @WithName("double")
    double doublePrimitive();

    @WithName("double")
    Double doubleWrapper();

    @WithName("char")
    char charPrimitive();

    @WithName("char")
    Character charWrapper();

    @WithName("boolean")
    boolean booleanPrimitive();

    @WithName("boolean")
    Boolean booleanWrapper();
}
application.properties
int=9
long=9999999999
float=99.9
double=99.99
char=c
boolean=true

This is also valid for Optional and friends:

@ConfigMapping
public interface Optionals {
    Optional<Server> server();

    Optional<String> optional();

    @WithName("optional.int")
    OptionalInt optionalInt();

    interface Server {
        String host();

        int port();
    }
}

In this case, the mapping won’t fail if there is no configuration property to match the mapping.

1.5.1. @WithConverter

The @WithConverter annotation provides a way to set a Converter to use in a specific mapping:

@ConfigMapping
public interface Converters {
    @WithConverter(FooBarConverter.class)
    String foo();
}

public static class FooBarConverter implements Converter<String> {
    @Override
    public String convert(final String value) {
        return "bar";
    }
}
application.properties
foo=foo

A call to Converters.foo() results in the value bar.

1.5.2. Collections

A config mapping is also able to map collections types List and Set:

@ConfigMapping(prefix = "server")
public interface ServerCollections {
    Set<Environment> environments();

    interface Environment {
        String name();

        List<App> apps();

        interface App {
            String name();

            List<String> services();

            Optional<List<String>> databases();
        }
    }
}
application.properties
server.environments[0].name=dev
server.environments[0].apps[0].name=rest
server.environments[0].apps[0].services=bookstore,registration
server.environments[0].apps[0].databases=pg,h2
server.environments[0].apps[1].name=batch
server.environments[0].apps[1].services=stock,warehouse

The List or Set mappings can use indexed properties to map configuration values in mapping groups. For collection with simple element types like String, their configuration value is a comma separated string.

Only the List mapping can maintain element order. Hence, with Set mappings the element order is not maintained from the configuration files but is random.

1.5.3. Maps

A config mapping is also able to map a Map:

@ConfigMapping(prefix = "server")
public interface Server {
    String host();

    int port();

    Map<String, String> form();
}
application.properties
server.host=localhost
server.port=8080
server.form.login-page=login.html
server.form.error-page=error.html
server.form.landing-page=index.html

The configuration property needs to specify an additional name to act as the key. In this case the form() Map will contain three elements with the keys login-page, error-page and landing-page.

It also works for groups:

@ConfigMapping(prefix = "server")
public interface Servers {
    @WithParentName
    Map<String, Server> allServers();
}

public interface Server {
    String host();

    int port();

    String login();

    String error();

    String landing();
}
application.properties
server."my-server".host=localhost
server."my-server".port=8080
server."my-server".login=login.html
server."my-server".error=error.html
server."my-server".landing=index.html

In this case the allServers() Map will contain one Server element with the key my-server.

1.6. Defaults

The @WithDefault annotation allows to set a default property into a mapping (and prevent and error if the configuration value is not available in any ConfigSource):

public interface Defaults {
    @WithDefault("foo")
    String foo();

    @WithDefault("bar")
    String bar();
}

No configuration properties required. The Defaults.foo() will return the value foo and Defaults.bar() will return the value bar.

1.7. Validation

A config mapping may combine annotations from Bean Validation to validate configuration values:

@ConfigMapping(prefix = "server")
public interface Server {
    @Size(min = 2, max = 20)
    String host();

    @Max(10000)
    int port();
}
For validation to work, the quarkus-hibernate-validator extension is required, and it is performed automatically.

1.8. Mocking

A mapping interface implementation is not a proxy, so it cannot be mocked directly with @InjectMock like other CDI beans. One trick is to make it proxyable with a producer method:

public class ServerMockProducer {
    @Inject
    Config config;

    @Produces
    @ApplicationScoped
    @io.quarkus.test.Mock
    Server server() {
        return config.unwrap(SmallRyeConfig.class).getConfigMapping(Server.class);
    }
}

The Server can be injected as a mock into a Quarkus test class with @InjectMock:

@QuarkusTest
class ServerMockTest {
    @InjectMock
    Server server;

    @Test
    void localhost() {
        Mockito.when(server.host()).thenReturn("localhost");
        assertEquals("localhost", server.host());
    }
}
The mock is just an empty shell without any actual configuration values.

If the goal is to only mock certain configuration values and retain the original configuration, the mocking instance requires a spy:

@ConfigMapping(prefix = "app")
public interface AppConfig {
    @WithDefault("app")
    String name();

    Info info();

    interface Info {
        @WithDefault("alias")
        String alias();
        @WithDefault("10")
        Integer count();
    }
}

public static class AppConfigProducer {
    @Inject
    Config config;

    @Produces
    @ApplicationScoped
    @io.quarkus.test.Mock
    AppConfig appConfig() {
        AppConfig appConfig = config.unwrap(SmallRyeConfig.class).getConfigMapping(AppConfig.class);
        AppConfig appConfigSpy = Mockito.spy(appConfig);
        AppConfig.Info infoSpy = Mockito.spy(appConfig.info());
        Mockito.when(appConfigSpy.info()).thenReturn(infoSpy);
        return appConfigSpy;
    }
}

The AppConfig can be injected as a mock into a Quarkus test class with @Inject:

@QuarkusTest
class AppConfigTest {
    @Inject
    AppConfig appConfig;

    @Test
    void localhost() {
        Mockito.when(appConfig.name()).thenReturn("mocked-app");
        assertEquals("mocked-app", server.host());

        Mockito.when(appConfig.info().alias()).thenReturn("mocked-alias");
        assertEquals("mocked-alias", server.info().alias());
    }
}
Nested elements need to be spied individually by Mockito.

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