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: among others Strings, ints, doubles, UUIDs, Lists (of serializable values) and Maps (where both keys and values are serializable). 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.
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.
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.
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")
public class StolenCodeExample {
@Inject private GuiceObjectMapperFactory factory;
@Inject private ConfigurationLoader<CommentedConfigurationNode> loader;
@Listener
public void enable(GamePreInitializationEvent event) {
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.