NBT

A java implementation of the NBT protocol for Minecraft Java Edition.

Specification

According to the specification, there are currently 13 different types of tags:

• The EndTag is only used to mark the end of a CompoundTag in its serialized state or an empty ListTag.

• The maximum depth of the NBT structure is 512. If the depth exceeds this restriction during serialization, deserialization or String conversion, a MaxDepthReachedException is thrown. This usually happens when a circular reference exists in the NBT structure. The NBT specification does not allow circular references, as there is no tag to represent this.

Example usage:

The following code snippet shows how to create a CompoundTag:

CompoundTag ct = new CompoundTag();

ct.put("byte", new ByteTag((byte) 1));
ct.put("double", new DoubleTag(1.234));
ct.putString("string", "stringValue");

An example how to use a ListTag:

ListTag<FloatTag> fl = new ListTag<>(FloatTag.class);

fl.add(new FloatTag(1.234f);
fl.addFloat(5.678f);

Nesting

All methods serializing instances or deserializing data track the nesting levels to prevent circular references or malicious data which could, when deserialized, result in thousands of instances causing a denial of service.

These methods have a parameter for the maximum nesting depth they are allowed to traverse. A value of 0 means that only the object itself, but no nested object may be processed.

If an instance is nested further than allowed, a MaxDepthReachedException will be thrown. A negative maximum depth will cause an IllegalArgumentException.

Some methods do not provide a parameter to specify the maximum depth, but instead use Tag.DEFAULT_MAX_DEPTH (512) which is also the maximum used in Minecraft.

Utility

There are several utility methods to make your life easier if you use this library.

NBTUtil

NBTUtil.write() lets you write a Tag into a gzip compressed or uncompressed file in one line (not counting exception handling). Files are gzip compressed by default.

Example usage:

NBTUtil.write(namedTag, "filename.dat");

NBTUtil.read() reads any file containing NBT data. No worry about compression, it will automatically uncompress gzip compressed files.

Example usage:

NamedTag namedTag = NBTUtil.read("filename.dat");

Playing Minecraft?

Each tag can be converted into an NBT String (SNBT) used in Minecraft commands.

Example usage:

CompoundTag c = new CompoundTag();
c.putByte("blah", (byte) 5);
c.putString("foo", "bär");
ListTag<StringTag> s = new ListTag<>(StringTag.class);
s.addString("test");
s.add(new StringTag("text"));
c.add("list", s);
System.out.println(SNBTUtil.toSNBT(c)); // {blah:5b,foo:"bär",list:[test,text]}

There is also a tool to read, change and write MCA files.

Here are some examples:

// This changes the InhabitedTime field of the chunk at x=68, z=81 to 0
MCAFile mcaFile = MCAUtil.readMCAFile("r.2.2.mca");
Chunk chunk = mcaFile.getChunk(68, 81);
chunk.setInhabitedTime(0);
MCAUtil.writeMCAFile("r.2.2.mca", mcaFile);

There is also an optimized api to retrieve and set block information (BlockStates) in MCA files.

Example:

// Retrieves block information from the MCA file
CompoundTag blockState = mcaFile.getBlockStateAt(1090, 25, 1301);

// Retrieves block information from a single chunk
CompoundTag blockState = chunk.getBlockStateAt(2, 25, 5);

// Set block information
CompoundTag stone = new CompoundTag();
stone.putString("Name", "minecraft:stone");
mcaFile.setBlockStateAt(1090, 25, 1301, stone, false);

To ensure good performance even when setting a lot of blocks and / or editing sections with a huge palette of block states, the size of the BlockStates array is only updated when the size of the palette requires it. This means there might be blocks in the palette that are not actually used in the BlockStates array. You can trigger a cleanup process by calling one of the following three methods, depending on the desired depth:

mcaFile.cleanupPalettesAndBlockStates();
chunk.cleanupPalettesAndBlockStates();
section.cleanupPaletteAndBlockStates();