Microprofile Config: Creating a Custom ConfigSource

In this post I’ll show you how can I create a custom ConfigSource to read properties from an external file. In this post I will not explain about what is Eclipse Microprofile Config, and if you want to know what is, access my last post Understanding Eclipse Microprofile Config .

The Eclipse Microprofile Config provide support to read configuration properties by a ConfigSource class. With this, if you need create a custom support to any configuration source (such as database, file system, service), you need create a custom ConfigSource class to provide this support.

In this example I create a ConfigSource to read configuration properties from an external file(outside of package), and the package will have only one property inside, that is the property to get the path of the file configuration. Bellow we have FileSystemConfigSource class that implementing ConfigSource.

public class FileSystemConfigSource implements ConfigSource {

    private final String FILE_CONFIG_PROPERTY = "net.rhuanrocha.mp-speaker.config.file.path";
    private final String CONFIG_SOURCE_NAME = "FileSystemConfigSource";
    private final int ORDINAL = 300;

    private String fileConfig;

    @Override
    public Map getProperties() {

        try(InputStream in = new FileInputStream( readPath() )){

            Properties properties = new Properties();
            properties.load( in );

            Map map = new HashMap();
            properties.stringPropertyNames()
                    .stream()
                    .forEach(key-> map.put(key, properties.getProperty(key)));

            return map;

        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    @Override
    public Set getPropertyNames() {

        try(InputStream in = new FileInputStream( readPath() )){

            Properties properties = new Properties();
            properties.load( in );

            return properties.stringPropertyNames();

        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    @Override
    public int getOrdinal() {
        return ORDINAL;
    }

    @Override
    public String getValue(String s) {

        try(InputStream in = new FileInputStream( readPath() )){

            Properties properties = new Properties();
            properties.load( in );

            return properties.getProperty(s);

        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    @Override
    public String getName() {
        return CONFIG_SOURCE_NAME;
    }

    public String readPath(){

        if(Objects.nonNull(fileConfig)){
            return fileConfig;
        }

        final Config cfg = ConfigProvider.getConfig();
        return fileConfig = cfg.getValue(FILE_CONFIG_PROPERTY, String.class);
    }

}

Furthermore, we need create a property in META-INF/microprofile-config.properties with the path of the external file, and put the config_ordinal property inside META-INF/microprofile-config.properties major then the ordinal of the FileSystemConfigSource, because the FileSystemConfigSource read the property from META-INF/microprofile-config.properties. Below we have the example.

config_ordinal = 400
net.rhuanrocha.mp-speaker.config.file.path=/etc/mp-speaker/config/configuration.properties

Note: My suggest is insert in META-INF/microprofile-config.properties only the property to path of external file and the config_ordinal property.

If you want to see more about this example, access the repository on github by: https://github.com/rhuan080/microprofile-example