Using configuration with Gridgo

Gridgo supports two types of configuration: a key-value config and an object-based config. Key-value configurations are usually good for storing application settings, similar to a properties file, or bean registration, similar to Spring bean. Object-based configurations on the other hand suitable for storing complex data structure, like when configuring GridgoContext. Refer to each section below to get more details about each type of configuration.

Key-value configuration

Key-value configurations in Gridgo are called Registry. A registry stores a mapping between a String and an arbitrary object. Two most basic operations are lookup() and register(), e.g:

var registry = new SimpleRegistry();
registry.register("numbers", new int[] {1, 2, 3});
var numbers = registry.lookup("numbers");

You can also pass a type to the lookup method, so result will be automatically casted the specified type:

var numbers = registry.lookup("numbers", int[].class);

And substitute placeholders in strings using values from Registry:

var someString = "mongodb://${mongodb.host}:${mongodb.port}";
var parsedString = registry.substitute(someString);

Some of the supported registries are:

• SimpleRegistry: a registry backed by a HashMap
• PropertiesFileRegistry: a registry backed by a properties file
• SystemEnvRegistry: a registry which corresponds to the system environment variables
• SystemPropertyRegistry: a registry which corresponds to the Java properties (e.g when using -D option)
• MultiSourceRegistry: a registry which contains other registries, so you can use multiple registries as if it was a single one.

There are some registries supported in gridgo-extras:

• SpringRegistry: a registry which is backed by Spring ApplicationContext
• TypeSafeRegistry: a registry which is backed by typesafe/config

Object-based configuration

Object-based configurations in Gridgo are called Configurator. They are a bit more advanced than Registry which can support hot-reload. But they don’t support looking up individual key inside the configurations. Rather they will return the whole configuration as a BElement.

// create an instance of configurator using TypeSafe
var configurator = TypeSafeConfigurator.ofResource("application.conf");

// register for configuration event
configurator.subscribe(event -> {
  if (event.isLoaded())
    System.out.println("Event loaded: " + event.asLoaded().getConfigObject());
  else if (event.isReloaded())
    System.out.println("Event reloaded: " + event.asLoaded().getConfigObject());
  else if (event.isFailed())
    event.asFailed().getCause().printStackTrace();
});

// start the configurator
configurator.start();

The configurator needs more work than Registry because it can support hot-reload and remote configuration (e.g using a Database or Zookeeper)

Some currently supported configurator

• TypeSafeConfigurator: configurator backed by TypeSafe, supporting JSON, HOCON
• YamlConfigurator: configurator using YAML format
• JsonConfigurator: configurator using JSON format

Tip

Most configurators are extended from ReplayEventDispatcher, that means you can subscribe whenever you want, all events will be replayed every time you subscribe.