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== Serialization and Deserialization ==
== Serialization and Deserialization ==
The primary use for Codecs is to serialize java objects to some serialized type, such as a JsonElement or a Tag, and to deserialize an serialized object back to its proper java type. This is accomplished with <code>Codec#encodeStart</code> and <code>Codec#parse</code>, respectively. Given a Codec<SomeJavaType> and a DynamicOps<SomeSerializedType>, we can convert instances of SomeJavaType to instances of SomeSerializedType and back.
The primary use for Codecs is to serialize java objects to some serialized type, such as a JsonElement or a Tag, and to deserialize a serialized object back to its proper java type. This is accomplished with <code>Codec#encodeStart</code> and <code>Codec#parse</code>, respectively. Given a Codec<SomeJavaType> and a DynamicOps<SomeSerializedType>, we can convert instances of SomeJavaType to instances of SomeSerializedType and back.
Each of these methods take a [[DynamicOps]] instance and an instance of the object we are serializing or deserializing, and returns a DataResult:
Each of these methods take a [[DynamicOps]] instance and an instance of the object we are serializing or deserializing, and returns a DataResult:
// deserialize some Tag instance back to a proper java object
// deserialize some Tag instance back to a proper java object
DataResult<SomeJavaType> result = someCodec.parse(NBTOps.INSTANCE, someTag );
DataResult<SomeJavaType> result = someCodec.parse(NBTOps.INSTANCE, someTag);
// serialize some java object to a JsonElement
// serialize some java object to a JsonElement
As previously mentioned, we can use <code>Codec.INT</code> for the integer codec, and <code>Registry.ITEM</code> for the Item codec. We don't have a builtin codec for list-of-blockpos, but we can use BlockPos.CODEC to create one.
As previously mentioned, we can use <code>Codec.INT</code> for the integer codec, and <code>Registry.ITEM</code> for the Item codec. We don't have a builtin codec for list-of-blockpos, but we can use BlockPos.CODEC to create one.
== Lists ==
==Lists==
The <code>Codec#listOf</code> instance method can be used to generate a codec for a List from an existing codec:
The <code>Codec#listOf</code> instance method can be used to generate a codec for a List from an existing codec:
<syntaxhighlight lang="java">
<syntaxhighlight lang="java">
// BlockPos.CODEC is a Codec<BlockPos>
// BlockPos.CODEC is a Codec<BlockPos>
Codec<List<BlockPos>> = BlockPos.CODEC.listOf();
Codec<List<BlockPos>> blockPosListCodec = BlockPos.CODEC.listOf();
</syntaxhighlight>
</syntaxhighlight>
Codec.STRING.fieldOf("name").codec());
Codec.STRING.fieldOf("name").codec());
JsonElement encodedPair = BOXED_INT_CODEC.encodeStart(JsonOps.INSTANCE, Pair.of(5, "cheese").result().get();
JsonElement encodedPair = PAIR_CODEC.encodeStart(JsonOps.INSTANCE, Pair.of(5, "cheese").result().get();
</syntaxhighlight>
</syntaxhighlight>
This codec serializes the above value to:
This codec serializes the above value to:
* BlockPlacer and BlockPlacerType
* BlockPlacer and BlockPlacerType
* ConfiguredDecorator and FeatureDecorator
* ConfiguredDecorator and FeatureDecorator
=== Registering MapCodecCodecs for Dispatch Subcodecs ===
When registering a subcodec to any dispatch codec registry, the registered subcodec should be an instance of MapCodecCodec, or the subcodec will be nested in its own object when serialized.
For example, suppose we register a single-field subcodec, where we use fieldOf-and-xmap to convert an int to our int-holding Thing:
<syntaxhighlight lang="java">
public record Thing(int n){}
public static Codec<Thing> CODEC = Codec.INT.fieldOf("n").codec().xmap(Thing::new, Thing::n);
</syntaxhighlight>
This results in this json when serialized:
<syntaxhighlight lang="json">
"some_thing":
{
"type": "ourmod:thing",
"value": {
"n": 5
}
}
</syntaxhighlight>
This occurs because xmap does not produce a MapCodecCodec, and if this nested object is not desired, then our registered subcodec must be a MapCodecCodec.
However, fieldOf() produces a MapCodec, which has a codec() method, which does produce a MapCodecCodec. We can rearrange our codec builder, which then produces a cleaner json:
<syntaxhighlight lang="java">
public static Codec<Thing> CODEC = Codec.INT // Primitive codec
.fieldOf("n") // MapCodec
.xmap(Thing::new, Thing::n) // MapCodec
.codec(); // MapCodecCodec! That's what we want.
</syntaxhighlight>
<syntaxhighlight lang="json">
"some_thing":
{
"type": "ourmod:thing",
"n": 5
}
</syntaxhighlight>
RecordCodecBuilder also produces MapCodecCodecs.
=External Links=
=External Links=
* [https://github.com/Mojang/DataFixerUpper/blob/master/src/main/java/com/mojang/serialization/Codec.java Codecs in Mojang's official public DataFixerUpper repository]
* [https://github.com/Mojang/DataFixerUpper/blob/master/src/main/java/com/mojang/serialization/Codec.java Codecs in Mojang's official public DataFixerUpper repository]
* [https://kvverti.github.io/Documented-DataFixerUpper/snapshot/com/mojang/serialization/Codec.html#flatXmap-java.util.function.Function-java.util.function.Function- Unofficial Codec Javadocs]
* [https://kvverti.github.io/Documented-DataFixerUpper/snapshot/com/mojang/serialization/Codec.html#flatXmap-java.util.function.Function-java.util.function.Function- Unofficial Codec Javadocs]