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 an interface with minimal metadata configuration and annotated with the @io.smallrye.config.ConfigMapping annotation.

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

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

1.4.2. @WithParentName

The @WithParent 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")
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 stategies:

  • 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 are not configuration properties 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.

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.

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 thevalue bar.

1.7. Validation

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

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

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

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.

2. @ConfigProperties (Deprecated)

This feature will be removed soon, please update your code base and use @ConfigMapping instead.

The @io.quarkus.arc.config.ConfigProperties annotation is able to group multiple related configuration values in its own class:

package org.acme.config;

import io.quarkus.arc.config.ConfigProperties;
import java.util.Optional;

@ConfigProperties(prefix = "greeting") (1)
public class GreetingConfiguration {

    private String message;
    private String suffix = "!"; (2)
    private Optional<String> name;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public String getSuffix() {
        return suffix;
    }

    public void setSuffix(String suffix) {
        this.suffix = suffix;
    }

    public Optional<String> getName() {
        return name;
    }

    public void setName(Optional<String> name) {
        this.name = name;
    }
}
1 prefix is optional. If not set then the prefix to be used will be determined by the class name. In this case it would still be greeting (since the Configuration suffix is removed). If the class were named GreetingExtraConfiguration then the resulting default prefix would be greeting-extra.
2 ! will be the default value if greeting.suffix is not set.

Inject the GreetingResource with CDI @Inject:

@Inject
GreetingConfiguration greetingConfiguration;

Another alternative style provided by Quarkus is to create GreetingConfiguration as an interface:

package org.acme.config;

import io.quarkus.arc.config.ConfigProperties;
import org.eclipse.microprofile.config.inject.ConfigProperty;
import java.util.Optional;

@ConfigProperties(prefix = "greeting")
public interface GreetingConfiguration {

    @ConfigProperty(name = "message") (1)
    String message();

    @ConfigProperty(defaultValue = "!")
    String getSuffix(); (2)

    Optional<String> getName(); (3)
}
1 The @ConfigProperty annotation is needed because the name of the configuration property that the method corresponds does not follow the getter method naming conventions.
2 In this case since name is not set, the corresponding property will be greeting.suffix.
3 It is unnecessary to specify the @ConfigProperty annotation because the method name follows the getter method naming conventions (greeting.name being the corresponding property) and no default value is required.

When using @ConfigProperties on a class or an interface, if the value of one of its fields is not provided, the application startup will fail, and a javax.enterprise.inject.spi.DeploymentException will be thrown. This does not apply to Optional fields and fields with a default value.

2.1. Additional notes on @ConfigProperties

When using a regular class annotated with @ConfigProperties the class doesn’t necessarily have to declare getters and setters. Having simple public non-final fields is valid as well.

Furthermore, the configuration classes support nested object configuration. Suppose there was a need to have an extra layer of greeting configuration named content that would contain a few fields:

@ConfigProperties(prefix = "greeting")
public class GreetingConfiguration {

    public String message;
    public String suffix = "!";
    public Optional<String> name;
    public ContentConfig content; (1)

    public static class ContentConfig {
        public Integer prizeAmount;
        public List<String> recipients;
    }
}
1 The name of the field (not the class name) will determine the name of the properties that are bound to the object.

Setting the properties would occur in the normal manner:

application.properties
greeting.message = hello
greeting.name = quarkus
greeting.content.prize-amount=10
greeting.content.recipients=Jane,John

Furthermore, classes annotated with @ConfigProperties can be annotated with Bean Validation annotations:

@ConfigProperties(prefix = "greeting")
public class GreetingConfiguration {

    @Size(min = 20)
    public String message;
    public String suffix = "!";

}
For validation to work, the quarkus-hibernate-validator extension is required.

2.2. Using same ConfigProperties with different prefixes

Quarkus also supports the use of the same @ConfigProperties object with different prefixes for each injection point using the io.quarkus.arc.config.@ConfigPrefix annotation. If GreetingConfiguration from above needs to be used for both the greeting prefix and the other prefix:

@ConfigProperties(prefix = "greeting")
public class GreetingConfiguration {

    @Size(min = 20)
    public String message;
    public String suffix = "!";

}
@ApplicationScoped
public class SomeBean {

    @Inject (1)
    GreetingConfiguration greetingConfiguration;

    @ConfigPrefix("other") (2)
    GreetingConfiguration otherConfiguration;

}
1 At this injection point greetingConfiguration will use the greeting prefix since that is what has been defined on @ConfigProperties.
2 At this injection point otherConfiguration will use the other prefix from @ConfigPrefix instead of the greeting prefix. Notice that in this case @Inject is not required.

2.3. Combining ConfigProperties with build time conditions

Quarkus allows you to define conditions evaluated at build time (@IfBuildProfile, @UnlessBuildProfile, @IfBuildProperty and @UnlessBuildProperty) to enable or not the annotations @ConfigProperties and @ConfigPrefix which gives you a very flexible way to map your configuration.

Let’s assume that the configuration of a service is mapped thanks to a @ConfigProperties and you don’t need this part of the configuration for your tests as it will be mocked, in that case you can define a build time condition like in the next example:

ServiceConfiguration.java

@UnlessBuildProfile("test") (1)
@ConfigProperties
public class ServiceConfiguration {
    public String user;
    public String password;
}
1 The annotation @ConfigProperties is considered if and only if the active profile is not test.

SomeBean.java

@ApplicationScoped
public class SomeBean {

    @Inject
    Instance<ServiceConfiguration> serviceConfiguration; (1)

}
1 As the configuration of the service could be missing, we need to use Instance<ServiceConfiguration> as type at the injection point.