NBT

A java implementation of the NBT protocol, including a way to implement custom tags.

---

Specification

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

Tag class	Superclass	ID	Payload
EndTag	Tag	0	None
ByteTag	NumberTag	1	1 byte / 8 bits, signed
ShortTag	NumberTag	2	2 bytes / 16 bits, signed, big endian
IntTag	NumberTag	3	4 bytes / 32 bits, signed, big endian
LongTag	NumberTag	4	8 bytes / 64 bits, signed, big endian
FloatTag	NumberTag	5	4 bytes / 32 bits, signed, big endian, IEEE 754-2008, binary32
DoubleTag	NumberTag	6	8 bytes / 64 bits, signed, big endian, IEEE 754-2008, binary64
ByteArrayTag	ArrayTag	7	IntTag's payload size, then size ByteTag's payloads
StringTag	Tag	8	ShortTag's payload length, then a UTF-8 string with size length
ListTag	Tag	9	ByteTag's payload tagId, then IntTag‘s payload size, then size tags’ payloads, all of type tagId
CompoundTag	Tag	10	Fully formed tags, followed by an EndTag
IntArrayTag	ArrayTag	11	IntTag's payload size, then size IntTag's payloads
LongArrayTag	ArrayTag	12	IntTag's payload size, then size LongTag's payloads

• 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 on how to use ListTag:

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

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

---

Utility

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

NBTUtil

NBTUtil.writeTag() 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.writeTag(tag, "filename.dat");

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

Tag tag = NBTUtil.readTag("filename.dat");

Playing Minecraft?

Each tag can be converted into a JSON-like NBT String used in Minecraft commands. Example usage:

CompoundTag c = new CompoundTag();
c.putByte("blah", (byte) 5);
c.putString("foo", "bär");
String s = c.toTagString();

//output: {blah:5b,foo:"bär"}

There are also some tools to read, change and write MCA files: For example:

//This changes the InhabitedTime field of the chunk at x=68, z=81 to 0

MCAFile mcaFile = MCAUtil.readMCAFile("r.2.2.mca");
CompoundTag tag = mcaFile.getChunkData(68, 81);
tag.getCompoundTag("Level").setLong("InhabitedTime", 0L);
MCAUtil.writeMCAFile("r.2.2.mca", mcaFile);

---

Custom tags

Interested in more advanced features, and the default NBT protocol just isn't enough? Simply create your own tags! There are 4 example classes in net.querz.nbt.custom that show how to implement custom tags:

Class	ID	Description
ObjectTag	90	A wrapper tag that serializes and deserializes any object using the default java serialization.
ShortArrayTag	100	In addition to the already existing ByteArrayTag, IntArrayTag and LongArrayTag.
CharTag	110	Character (char) tag.
StructTag	120	Similar to the ListTag, but with the ability to store multiple types.

To be able to use a custom tag with deserialization, it needs to have a public no-args constructor and its id and class must be registered during runtime with TagFactory.registerCustomTag().