Serializing Objects

The Configurate library also provides the means to tweak automatic serialization and deserialization of objects. Per default, a set of data types can be (de)serialized:

Notitie

If you need special constraints or rules for your serialization (such as sorting the elements in a Set), then you should consider using your own TypeSerializer implementations.

But if you want to write your custom data structures to a config file, this will not be enough.

Imagine a data structure tracking how many diamonds a player has mined. It might look a little like this:

public class DiamondCounter {
    private UUID playerUUID;
    private int diamonds;

    [...]
}

Also assume some methods to access those fields, a nice constructor setting both of those etc.

Creating a Custom TypeSerializer

A very straightforward way of writing and loading such a data structure is providing a custom TypeSerializer. The TypeSerializer interface provides two methods, one to write the data from an object to a configuration node and one to create an object from a given configuration node.

import com.google.common.reflect.TypeToken;
import ninja.leaping.configurate.objectmapping.ObjectMappingException;
import ninja.leaping.configurate.objectmapping.serialize.TypeSerializer;

public class DiamondCounterSerializer implements TypeSerializer<DiamondCounter> {

    @Override
    public DiamondCounter deserialize(TypeToken<?> type, ConfigurationNode value)
      throws ObjectMappingException {
        UUID player = value.getNode("player").getValue(TypeToken.of(UUID.class));
        int diamonds = value.getNode("diamonds").getInt();
        return new DiamondCounter(player, diamonds);
    }

    @Override
    public void serialize(TypeToken<?> type, DiamondCounter obj, ConfigurationNode value)
      throws ObjectMappingException {
        value.getNode("player").setValue(obj.getPlayerUUID());
        value.getNode("diamonds").setValue(obj.getDiamonds());
    }
}

This TypeSerializer must then be registered with Configurate. This can be done either globally, by registering to the default TypeSerializerCollection or locally, by specifying it in the ConfigurationOptions when loading your config.

Notitie

ConfigurationOptions are immutable. Every time you try to modify the original instance a new instance is created; so you either have to use the (chained) result directly or update your variable accordingly.

Code Example: Registering a TypeSerializer globally

import ninja.leaping.configurate.objectmapping.serialize.TypeSerializers;

TypeSerializers.getDefaultSerializers().registerType(TypeToken.of(DiamondCounter.class), new DiamondCounterSerializer());

Code Example: Registering a TypeSerializer locally

import ninja.leaping.configurate.ConfigurationNode;
import ninja.leaping.configurate.ConfigurationOptions;
import ninja.leaping.configurate.objectmapping.serialize.TypeSerializerCollection;
import ninja.leaping.configurate.objectmapping.serialize.TypeSerializers;

TypeSerializerCollection serializers = TypeSerializers.getDefaultSerializers().newChild();
serializers.registerType(TypeToken.of(DiamondCounter.class), new DiamondCounterSerializer());
ConfigurationOptions options = ConfigurationOptions.defaults().setSerializers(serializers);
ConfigurationNode rootNode = someConfigurationLoader.load(options);

Waarschuwing

If you provide a custom TypeSerializer for types that are not introduced by your own plugin, you should only ever register them locally in order to avoid conflicts with other plugins or Sponge, caused by a TypeSerializer being overwritten.

Tip

If you need the TypeToken.of(DiamondCounter.class) in multiple places, then you should consider creating a constant for it. You can do it in a similar fashion as Sponge does in the TypeTokens class, or just define the constant inside of your data or serializer class.

Using ObjectMappers

Since in many cases the (de)serialization boils down to mapping fields to configuration nodes, writing such a TypeSerializer is a rather dull affair and something we’d like Configurate to do on its own. So let’s annotate our class with the ConfigSerializable and Setting annotations.

import ninja.leaping.configurate.objectmapping.Setting;
import ninja.leaping.configurate.objectmapping.serialize.ConfigSerializable;

@ConfigSerializable
public class DiamondCounter {

    @Setting(value="player", comment="Player UUID")
    private UUID playerUUID;
    @Setting(comment="Number of diamonds mined")
    private int diamonds;

    [...]
}

The above example can now be serialized and deserialized from config nodes without further registration. The @Setting annotations map a configuration node to the field that was annotated. It accepts two optional parameters, value and comment. If the value parameter exists, it defines the name of the node the field will be saved in. If it is not present, the name of the field will be used instead. So in our above example, the annotation ensures that the contents of the field playerUUID are saved to the node “player”, commented with “Player UUID”. The diamonds field however will be saved under that exact name since its annotation only specifies a comment. That comment will be written to the config if the implementation supports commented configuration nodes, otherwise it will be discarded.

Tip

You may also use the shorthand @Setting("someNode") instead of @Setting(value="someNode")

The @ConfigSerializable annotation eliminates the need for any registration since it allows Configurate to just generate an ObjectMapper for the class. The only limitation is that Configurate needs an empty constructor to instantiate a new object before filling in the annotated fields.

Notitie

You can also have fields that are not are not annotated with @Setting in your @ConfigSerializable classes. These fields won’t be persisted to config files and can be used to store temporary references for your plugin.

Using Default Values in ConfigSerializable Types

It is also possible to use default values inside of @ConfigSerializable types. You just have to use Java’s field initializers (or getters) to set some default values. As long as the entry is not present in the config file the value won’t be overwritten.

@ConfigSerializable
public class DiamondCounter {

    @Setting(value="player", comment="Player UUID")
    private UUID playerUUID;

    @Setting(comment="Number of diamonds mined")
    private int diamonds = 0;

    @Setting(comment="The time the player found a diamond last.")
    private LocalDateTime diamonds = LocalDateTime.now();

    [...]
}

Example: Loading a ConfigSerializable Config with Default Values

Instead of loading a default config from the plugin jar itself, it is also possible to just ask Configurate to create it if it is missing.

try {
    this.config = this.configManager.load().<Configuration>getValue(Configuration.TYPE, Configuration::generateDefault);
} catch (ObjectMappingException | IOException e) {
    this.logger.error("Failed to load the config - Using a default", e);
    this.config = Configuration.generateErrorDefault();
}

In this case you load the entire configuration into a Configuration object that contains all of your plugins configuration. Using such a class has the following benefits:

  • Type safety is guaranteed

  • No need to update the configuration file shipped in your plugin

  • You don’t need to store lots of references for each of your configuration options

  • You can pass this config (or its parts) into methods or reference it from other classes

  • It is easy to write comments for each attribute in a place that also helps you during development

Notitie

In this case Configuration.generateDefault() is called when the config file is missing or empty. If you still want to load the shipped default config asset you can load it inside of that method. Configuration.generateErrorDefault() is called when there is an error reading or parsing the config. It is not necessary to use separate methods for those cases; you can also use the no-arg constructor, or use an entirely custom solution.

Example: Saving a ConfigSerializable Config

Saving a @ConfigSerializable config is also very simple, as shown by the following example:

try {
    this.configManager.save(this.configManager.createEmptyNode().setValue(Configuration.TYPE, this.config));
} catch (IOException | ObjectMappingException e) {
    this.logger.error("Failed to save the config", e);
}

Providing a custom ObjectMapperFactory

That restriction, however, can be lifted if we use a different ObjectMapperFactory, for example a GuiceObjectMapperFactory. Instead of requiring an empty constructor, it will work on any class that guice can create via dependency injection. This also allows for a mixture of @Inject and @Setting annotated fields.

Your plugin can just acquire a GuiceObjectMapperFactory simply by dependency injection (see Dependency Injection) and then pass it to the ConfigurationOptions.

import org.spongepowered.api.event.Listener;
import org.spongepowered.api.event.game.state.GamePreInitializationEvent;
import org.spongepowered.api.plugin.Plugin;
import com.google.inject.Inject;
import ninja.leaping.configurate.commented.CommentedConfigurationNode;
import ninja.leaping.configurate.loader.ConfigurationLoader;
import ninja.leaping.configurate.objectmapping.GuiceObjectMapperFactory;

@Plugin(name="IStoleThisFromZml", id="shamelesslystolen", version="0.8.15", description = "Stolen")
public class StolenCodeExample {

    @Inject private GuiceObjectMapperFactory factory;
    @Inject private ConfigurationLoader<CommentedConfigurationNode> loader;

    @Listener
    public void enable(GamePreInitializationEvent event) throws IOException, ObjectMappingException {
        CommentedConfigurationNode node =
          loader.load(ConfigurationOptions.defaults().setObjectMapperFactory(factory));
        DiamondCounter myDiamonds = node.getValue(TypeToken.of(DiamondCounter.class));
    }
}

Notitie

The above code is an example and, for brevity, lacks proper exception handling.