Load multiple properties files from different paths. Useful when working with MicroProfile and Quarkus. Put your filepaths, separated by colon (like the PATH variable) in the PROPERTIES_FILES environment variable.

MultipleFilesConfigSource.java

package it.alfonsopauciello.config;

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

import java.io.FileReader;
import java.util.Properties;
import java.util.Set;

public class MultipleFilesConfigSource implements ConfigSource {
  private static final Properties configuration = new Properties();

  static void loadProperties(final String files) {
    if (files == null || files.length() <= 0) {
      return;
    }
    for (final String fpath : files.split(":")) {
      FileReader reader = null;
      try {
        reader = new FileReader(fpath);
        final Properties prop = new Properties();
        prop.load(reader);
        configuration.putAll(prop);
      } catch (Exception e) {
        configuration.clear();
        throw new RuntimeException(e);
      } finally {
        if (reader != null) {
          try {
            reader.close();
          } catch (Exception e) {
            e.printStackTrace();
          }
        }
      }
    }
  }

  static void clear() {
    configuration.clear();
  }

  static {
    loadProperties(System.getenv("PROPERTIES_FILES"));
  }

  @Override
  public int getOrdinal() {
    return 275;
  }

  @Override
  public Set<String> getPropertyNames() {
    return configuration.stringPropertyNames();
  }

  @Override
  public String getValue(final String propertyName) {
    return configuration.getProperty(propertyName);
  }

  @Override
  public String getName() {
    return MultipleFilesConfigSource.class.getSimpleName();
  }
}

MultipleFilesConfigSourceTest.java

package it.alfonsopauciello.config;

import io.quarkus.test.junit.QuarkusTest;
import org.eclipse.microprofile.config.ConfigProvider;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

@QuarkusTest
public class MultipleFilesConfigSourceTest {
  private static final String FILES_VALID =
    "./src/test/resources/application_unit_test_1.properties" + ":" +
      "./src/test/resources/application_unit_test_2.properties";

  private static final String FILES_INVALID =
    "./src/test/resources/application_unit_test_1.properties" + ":" +
      "./src/test/resources/i_am_inexistent.properties";

  @BeforeEach
  public void clearProperties() {
    MultipleFilesConfigSource.clear();
  }

  @Test
  public void checkValidFile() {
    MultipleFilesConfigSource.loadProperties(FILES_VALID);

    // Regular properties file
    Assertions.assertFalse(ConfigProvider.getConfig().getOptionalValue("quarkus.log.category.\"it.infocert\".level", String.class).isEmpty());

    // Custom properties file 1
    Assertions.assertEquals("true", ConfigProvider.getConfig().getValue("check.one", String.class));
    Assertions.assertEquals("false", ConfigProvider.getConfig().getValue("check.two", String.class));
    Assertions.assertTrue(ConfigProvider.getConfig().getOptionalValue("check.three", String.class).isEmpty());
  }

  @Test
  public void checkNonExistentFile() {
    Assertions.assertThrows(RuntimeException.class, () -> MultipleFilesConfigSource.loadProperties(FILES_INVALID));

    // Regular properties file
    Assertions.assertFalse(ConfigProvider.getConfig().getOptionalValue("quarkus.log.category.\"it.infocert\".level", String.class).isEmpty());

    // Custom properties file 1
    Assertions.assertTrue(ConfigProvider.getConfig().getOptionalValue("check.one", String.class).isEmpty());
    Assertions.assertTrue(ConfigProvider.getConfig().getOptionalValue("check.two", String.class).isEmpty());
    Assertions.assertTrue(ConfigProvider.getConfig().getOptionalValue("check.three", String.class).isEmpty());
  }
}