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Saved Data

The Saved Data (SD) system can be used to save additional data on levels.

If the data is specific to some block entities, chunks, or entities, consider using a data attachment instead.

Declaration​

Each SD implementation must subtype the SavedData class. There are two important methods to be aware of:

  • save: Allows the implementation to write NBT data to the level.
  • setDirty: A method that must be called after changing the data, to notify the game that there are changes that need to be written. If not called, #save will not get called and the existing data will persist.

Attaching to a Level​

Any SavedData is loaded and/or attached to a level dynamically. As such, if one is never created on a level, then it will not exist.

SavedDatas are created and loaded from the DimensionDataStorage, which can be accessed by either ServerChunkCache#getDataStorage or ServerLevel#getDataStorage. From there, you can get or create an instance of your SD by calling DimensionDataStorage#computeIfAbsent. This will attempt to get the current instance of the SD if present or create a new one and load all available data.

DimensionDataStorage#computeIfAbsent takes in three arguments: a function to load NBT data into a SD and return it, a supplier to construct a new instance of the SD, and the name of the .dat file stored within the data folder for the implemented level.

For example, if a SD was named "example" within the Nether, then a file would be created at ./<level_folder>/DIM-1/data/example.dat and would be implemented like so:

// In some class
public ExampleSavedData create() {
  return new ExampleSavedData();
}

public ExampleSavedData load(CompoundTag tag) {
  ExampleSavedData data = this.create();
  // Load saved data
  return data;
}

// In some method within the class
netherDataStorage.computeIfAbsent(this::load, this::create, "example");

To persist a SD across levels, a SD should be attached to the Overworld, which can be obtained from MinecraftServer#overworld. The Overworld is the only dimension that is never fully unloaded and as such makes it perfect to store multi-level data on.