Java 8 Type-Safe Configuration with default methods

There is a common requirement in most of the Java/JavaEE projects related to how to differentiate environment configurations like development, test, QA, production, etc. for that reason there are a lot of frameworks or libraries to resolve that:

• DeltaSpike Configuration
• Apache Commons Configuration
• Sabot
• Apache Tamaya
• Dropwizard Configuration
• Jackson Dataformat YAML

Even there is a Java Specification Request (JSR) Proposal:

• JSR Proposal

How those libraries resolve the problem

Most of those libraries require to have an injection point(s) for the configurations and also the source of the configuration(s), something like this:

dev.properties:

host=localhost
port=5432
schema=public

prod.properties:

host=production.com
port=5432
schema=public

ConfigurationResolver.java:

class ConfigurationResolver implements SomeLibraryInterface {
  @Override
  public String resolvePropertyFilename() {
    // probably do some trick to load a global/base configuration
    // if is not provided for the library
    return String.format("%s.properties", System.getProperty("MY_ENV", "dev"));
  }
}

MyType.java:

class MyType {
  @Configuration(key = "host")
  String host;
  @Configuration(key = "port")
  int port;
  @Configuration(key = "schema", defaultValue = "public")
  String schema;
}

Notice that all the granularity is only needed because of lack of support for custom types

Besides that, with the new Java 8 capabilities, specifically with default methods and some utility classes are easy to get this behavior.

With Java 8 default methods

DefaultConfiguration.java:

interface DefaultConfiguration {
  default DataSource datasource {
    // create the DS with host, port and schema
    return new MyDataSource("localhost", 5432, "public");
  }
}

DevConfiguration.java:

class DevConfiguration implements DefaultConfiguration {
  // No need to override methods if they are the same
}

ProdConfiguration:

class ProdConfiguration implements DefaultConfiguration {
  default DataSource datasource {
    return new MyDataSource("production.com", 5432, "public");
  }
}

ConfigurationFactory.java:

abstract class ConfigurationFactory {
    private static final Map<String, DefaultConfiguration> configurations = new HashMap<>();

    static {
        configurations.put("development", new DevConfiguration());
        configurations.put("production", new ProdConfiguration());
    }

    public static DefaultConfiguration configuration() {
        return configurations.getOrDefault(System.getProperty("MY_ENV"), new DevConfiguration());
    }
}

Notice that you can use an enumeration instead of a map as a configuration factory.

Pros

• Typesafe configurations
• Support for all kinds of types not only String, Date or primitives. you can specify or example DataSource, TimeUnits, JedisPool, etc.
• No conversion/mapping from strings to types
• No more .properties, .xml or .yml files
• Possibility to use other sources to fill the properties like properties files, database, rest API's, etc.
• No library/framework/dependency required in your app

Cons

• Changes in the configuration require to compile/deploy (this shouldn’t be a problem in the 99% of the cases)

source code