Exoconf

Exoconf is a small library to manage configuration for Java 9+. Exoconf supports turning configuration into objects using Exobytes by pulling configuration from different sources, like files in an easy to write format and environment variables.

Config config = Config.create()
  .addFile("example.conf")
  .build();

Optional<String> value = config.get("path.to.value", String.class);

License

This project is licensed under the MIT license, see the file LICENSE.md for details.

Usage via Maven

<dependency>
  <groupId>se.l4.exoconf</groupId>
  <artifactId>exoconf</artifactId>
  <version>1.0.0</version>
</dependency>

Configuration format

The format of configuration files is similar to JSON but more lenient in how things are specified, such as not having to use quotes, colons (:) can be excluded at times and equals can replaced :.

Example:

thumbnails {
  medium {
    width: 200
    height: 200
  }
}

If the above file is used the value can be fetched from the Config:

Optional<Integer> width = config.get("thumbnails.medium.width", Integer.class);

Environment overrides

Exoconf supports environment variables as a source, in which case they can be used to provide new properties or override existing properties. When Exoconf is asked for a property it will try to get a an environment variable according to these rules:

• First the exact name will be tried, such as asking for get("MEDIUM_WIDTH") will look for MEDIUM_WIDTH
• Second all non-ASCII characters will be replaced with _, so that asking for get("medium.width") would match medium_width
• Third everything is uppercased, so that get("medium.width") would match MEDIUM_WIDTH.

For example, something like this can be used override the thumbnails.medium.width value:

$ THUMBNAILS_MEDIUM_WIDTH=300 java ...

Using serialization

Exoconf can turn configuration properties into an object by specifying a call that uses serialization:

@AnnotationSerialization
public class ThumbnailSize {
  @Expose
  public int width;

  @Expose
  public int height;
}

The class can then be specified when using get:

Optional<ThumbnailSize> mediumSize = config.get("thumbnails.medium", ThumbnailSize.class);

Validation of config properties

Exoconf supports validating objects using Bean Validation. To activate this set a ValidatorFactory when building the Config instance:

Config.create()
  .withValidatorFactory(validatorFactory)
  .build();

When this factory is present it's possible to annotate fields in classes with limits:

@AnnotationSerialization
public class ThumbnailSize {
  @Expose
  @Min(100) @Max(2000)
  public int width;

  @Expose
  @Min(100) @Max(2000)
  public int height;
}

These limits will then be checked when get is called:

Optional<ThumbnailSize> mediumSize = config.get("thumbnails.medium", ThumbnailSize.class);