SmallRye Config 1.9 Released

In SmallRye Config 1.9 we continue our innovation and experimentation model, by bringing additional features and enhancements to the API. This release introduces the following big changes:

Config Mappings

A Config Mapping provides a way to group multiple configuration properties into a single cohesive API. A Config Mapping requires a simple interface with minimal metadata configuration.

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

    int port();

The Server interface retrieves and maps configuration properties with the name into the and server.port into Server.port() method. The configuration property name to lookup builds from the @ConfigMapping annotation prefix and the method name with . (dot) as the separator. The @ConfigMapping annotation is used to auto-discover and register these mapping interfaces in a CDI aware environment. In non-CDI environments, register the Config Mapping via SmallRyeConfigBuilder#withMapping.

To retrieve such Config Mapping, a simple @Inject in any CDI aware bean is enough:

Server server;

void businessMethod() {
    String host =;

To retrieve the Config Mapping in non-CDI environments use the API io.smallrye.config.SmallRyeConfig#getConfigMapping:

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

Additionally, Config Mappings also support:

  • Automatic conversion of the configuration type.

  • Nested Config Mapping groups.

  • Validate if configuration properties exist at the startup.

  • Map, Optional, and primitive types.

  • @WithName to override the property name.

  • @WithConverter to override the converter to use.

  • @WithDefault to set the default value if none is found in the config sources.

Combining all of these features, we can write a Config Mapping that looks like this:

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

    int port();

    Duration timeout();

    int threads();

    Map<String, String> form();

    Optional<Ssl> ssl();

    Optional<Proxy> proxy();

    Log log();

    interface Ssl {
        int port();

        String certificate();

        List<String> protocols();

    interface Proxy {
        boolean enable();

    interface Log {
        boolean enabled();

        String suffix();

        boolean rotate();

        Pattern pattern();

        enum Pattern {

For additional information, check out our documentation about Config Mappings and the example in the SmallRye Config Github repo.

In MicroProfile Config 2.0, an initial version for this feature will be available. It doesn’t support all the features implemented in SmallRye Config, but the plan is to keep evolving and add more functionality based on the feedback of the community. You can read more about it here.

Configurable Config Sources

A highly requested feature is the ability to configure custom Config Sources, meaning it should be possible to retrieve configuration values from other sources before building our own. Take for instance a Database based Config Source. Such a source requires additional configurations like URL, username, and password to connect to the database. Where do we set these configurations?

The new ConfigSourceFactory API provides a context with access to the currently available configuration. With a ConfigSourceFactory, it is possible to bootstrap a ConfigSource that configures itself with other sources.

The ConfigSourceFactory requires the implementation of a single method ConfigSource getConfigSource(ConfigSourceContext context):

public class ConfigMapConfigSourceFactory implements ConfigSourceFactory {
    public ConfigSource getConfigSource(final ConfigSourceContext context) {
        final ConfigValue value = context.getValue("");
        if (value == null || value.getValue() == null) {
            throw new IllegalArgumentException("CONFIG_MAP_DIR_SOURCE not defined");

        return new FileSystemConfigSource(value.getValue());

The provided ConfigSourceContext may call a single method ConfigValue getValue(String name). This method lookups configuration names in all sources already initialized by the Config even if they have a lower priority than the one defined in the ConfigSourceFactory. A`ConfigSource` produced by a ConfigSourceFactory is not taken into account to configure other sources produced by lower priority ConfigSourceFactory. To register a ConfigSourceFactory use the standard Java ServiceLoader.

For additional information, check out our documentation about Config Mappings and the example in the SmallRye Config Github repo.

Default Values

Right now, the only way to set a default value for a configuration to use the org.eclipse.microprofile.config.inject.ConfigProperty#defaultValue. This has a few limitations. It doesn’t work in the programmatic lookup or if we are using the annotation and have to inject the same property in multiple places, we need to duplicate the default value in each injection point. Adding the configuration values into to act as a default is not optimal either, since they may override lower priority custom sources.

SmallRye Config adds a simple API to set such default values, with SmallRyeConfigBuilder#withDefaultValue(String name, String value) or SmallRyeConfigBuilder#withDefaultValue(Map<String, String> defaultValues).

Default values for any configuration name can then be supplied with these APIs. SmallRye Config will only fallback to these default if no value is found in the available sources.

The Default values API also supports name patterns. For instance a withDefaultValue("smallrye.*", "1234") provides default values for any configuration name with the prefix smallrye.


All the new features detailed here are experimental. The team is happy with them, and they had careful consideration when designed. We cannot guarantee that they won’t suffer any changes in the next few releases, especially considering that the SmallRye team is also pushing to have these added to the MicroProfile Config specification, which may require some changes.

This shouldn’t discourage developers to use these new features. We believe these add a lot of utility and improve the developer experience when setting configurations in applications.

A handful of other small improvements and bugs fixes are also included in this release. Check them out in the Release Notes

Please, feel free to drop us any feedback to the SmallRye Mailing List.