Config Source Factory

Another way to create a ConfigSource is via the ConfigSourceFactory. The difference between the SmallRye Config Factory and the standard way to make a ConfigSource as specified in MicroProfile Config is the Factory’s ability to provide a context with access to the available configuration. With the ConfigSourceFactory it is possible to bootstrap a ConfigSource that configures itself with previously initialized ConfigSource's.

By implementing ConfigSourceFactory, a list of ConfigSource's may be provided via the Iterable<ConfigSource> getConfigSources(ConfigSourceContext context) method. The ConfigSourceFactory may also assign a priority by overriding the default method OptionalInt getPriority(). The priority only sorts the factories during initialization. After initialization, the provided ConfigSources will use their own ordinal and sorted with all ConfigSources available in the Config instance.

When the Factory initializes, the provided ConfigSourceContext may call the method ConfigValue getValue(String name). This method looks up configuration names in all ConfigSource's already initialized by the Config instance, including sources with lower ordinals than the ones defined in the ConfigSourceFactory. The ConfigSourceFactory does not consider ConfigSources's provided by other ConfigSourceFactory's (the priority does not matter).

Registration of a ConfigSourceFactory is done via the ServiceLoader mechanism by providing the implementation classes in a META-INF/services/io.smallrye.config.ConfigSourceFactory file. Alternatively, factories may be registered via the Programmatic API in SmallRyeConfigBuilder#withSources.

A ConfigSourceFactory requires an implementation of io.smallrye.config.ConfigSourceFactory. Each implementation requires registration via the ServiceLoader mechanism in the META-INF/services/io.smallrye.config.ConfigSourceFactory file. Alternatively, interceptors may be registered via the Programmatic API in SmallRyeConfigBuilder#withSources.

package org.acme.config

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.Collections;
import java.util.List;

import org.eclipse.microprofile.config.spi.ConfigSource;

import io.smallrye.config._private.ConfigMessages;
import io.smallrye.config.PropertiesConfigSource;
import io.smallrye.config.ConfigSourceContext;
import io.smallrye.config.ConfigSourceFactory;
import io.smallrye.config.ConfigValue;

public class FileSystemConfigSourceFactory implements ConfigSourceFactory {
    @Override
    public Iterable<ConfigSource> getConfigSources(final ConfigSourceContext context) {
        final ConfigValue value = context.getValue("org.acme.config.file.locations");
        if (value == null || value.getValue() == null) {
            return Collections.emptyList();
        }

        try {
            return List.of(new PropertiesConfigSource(toURL(value.getValue()), 250));
        } catch (IOException e) {
            return Collections.emptyList();
        }
    }

    private URL toURL(final String value) {
        try {
            return new URI(value).toURL();
        } catch (URISyntaxException | MalformedURLException e) {
            throw ConfigMessages.msg.uriSyntaxInvalid(e, value);
        }
    }
}

And registration in:

META-INF/services/io.smallrye.config.ConfigSourceFactory

org.acme.config.FileSystemConfigSourceFactory

The FileSystemConfigSourceFactory look ups the configuration value for org.acme.config.file.locations, and uses it to set up an additional ConfigSource.

Alternatively, a ConfigurableConfigSourceFactory accepts a ConfigMapping interface to configure the ConfigSource:

@ConfigMapping(prefix = "org.acme.config.file")
interface FileSystemConfig {
    List<URL> locations();   
}

public class FileSystemConfigurableConfigSourceFactory implements ConfigurableConfigSourceFactory<FileSystemConfig> {
    @Override
    public Iterable<ConfigSource> getConfigSources(ConfigSourceContext context, FileSystemConfig config) {

    }
}

With a ConfigurableConfigSourceFactory it is not required to look up the configuration values with ConfigSourceContext. The values are automatically mapped with the defined @ConfigMapping.