Development resources/Example NBT Class

This Java class will read an NBT structure and return the topmost tag from an InputStream and let you write an NBT structure through the topmost tag to an OutputStream.

import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.util.zip.GZIPInputStream; import java.util.zip.GZIPOutputStream; /** * NBT IO class *  * @see Online NBT specification */ public class Tag { private final Type type; private Type listType = null; private final String name; private Object value; /** 	 * Enum for the tag types. */ 	public enum Type { TAG_End, TAG_Byte, TAG_Short, TAG_Int, TAG_Long, TAG_Float, TAG_Double, TAG_Byte_Array, TAG_String, TAG_List, TAG_Compound } 	/** 	 * Create a new TAG_List or TAG_Compound NBT tag. * 	 * @param type either TAG_List or TAG_Compound * @param name name for the new tag or  to create an unnamed tag. * @param value list of tags to add to the new tag. */ 	public Tag(Type type, String name, Tag[] value) { this(type, name, (Object) value); } 	/** 	 * Create a new TAG_List with an empty list. Use {@link Tag#addTag(Tag)} to add tags later. * 	 * @param name name for this tag or   to create an unnamed tag. * @param listType type of the elements in this empty list. */ 	public Tag(String name, Type listType) { this(Type.TAG_List, name, listType); } 	/** 	 * Create a new NBT tag. * 	 * @param type any value from the   enum. * @param name name for the new tag or  to create an unnamed tag. * @param value an object that fits the tag type or a  to create an empty TAG_List with this list type. */ 	public Tag(Type type, String name, Object value) { if (type == Type.TAG_Compound) if (!(value instanceof Tag[])) throw new IllegalArgumentException; switch (type) { case TAG_End: if (value != null) throw new IllegalArgumentException; break; case TAG_Byte: if (!(value instanceof Byte)) throw new IllegalArgumentException; break; case TAG_Short: if (!(value instanceof Short)) throw new IllegalArgumentException; break; case TAG_Int: if (!(value instanceof Integer)) throw new IllegalArgumentException; break; case TAG_Long: if (!(value instanceof Long)) throw new IllegalArgumentException; break; case TAG_Float: if (!(value instanceof Float)) throw new IllegalArgumentException; break; case TAG_Double: if (!(value instanceof Double)) throw new IllegalArgumentException; break; case TAG_Byte_Array: if (!(value instanceof byte[])) throw new IllegalArgumentException; break; case TAG_String: if (!(value instanceof String)) throw new IllegalArgumentException; break; case TAG_List: if (value instanceof Type) { this.listType = (Type) value; value = new Tag[0]; } else { if (!(value instanceof Tag[])) throw new IllegalArgumentException; this.listType = (((Tag[]) value)[0]).getType; } 			break; case TAG_Compound: if (!(value instanceof Tag[])) throw new IllegalArgumentException; break; default: throw new IllegalArgumentException; } 		this.type = type; this.name = name; this.value = value; } 	public Type getType { return type; } 	public String getName { return name; } 	public Object getValue { return value; } 	public Type getListType { return listType; } 	/** 	 * Add a tag to a TAG_List or a TAG_Compound. */ 	public void addTag(Tag tag) { if (type != Type.TAG_List && type != Type.TAG_Compound) throw new RuntimeException; Tag[] subtags = (Tag[]) value; insertTag(tag, subtags.length); } 	/** 	 * Add a tag to a TAG_List or a TAG_Compound at the specified index. */ 	public void insertTag(Tag tag, int index) { if (type != Type.TAG_List && type != Type.TAG_Compound) throw new RuntimeException; Tag[] subtags = (Tag[]) value; if (subtags.length > 0) if (type == Type.TAG_List && tag.getType != getListType) throw new IllegalArgumentException; if (index > subtags.length) throw new IndexOutOfBoundsException; Tag[] newValue = new Tag[subtags.length + 1]; System.arraycopy(subtags, 0, newValue, 0, index); newValue[index] = tag; System.arraycopy(subtags, index, newValue, index + 1, subtags.length - index); value = newValue; } 	/** 	 * Remove a tag from a TAG_List or a TAG_Compound at the specified index. * 	 * @return the removed tag */ 	public Tag removeTag(int index) { if (type != Type.TAG_List && type != Type.TAG_Compound) throw new RuntimeException; Tag[] subtags = (Tag[]) value; Tag victim = subtags[index]; Tag[] newValue = new Tag[subtags.length - 1]; System.arraycopy(subtags, 0, newValue, 0, index); index++; System.arraycopy(subtags, index, newValue, index - 1, subtags.length - index); value = newValue; return victim; } 	/** 	 * Remove a tag from a TAG_List or a TAG_Compound. If the tag is not a child of this tag then nested tags are searched. * 	 * @param tag tag to look for */ 	public void removeSubTag(Tag tag) { if (type != Type.TAG_List && type != Type.TAG_Compound) throw new RuntimeException; if (tag == null) return; Tag[] subtags = (Tag[]) value; for (int i = 0; i < subtags.length; i++) { if (subtags[i] == tag) { removeTag(i); return; } else { if (subtags[i].type == Type.TAG_List || subtags[i].type == Type.TAG_Compound) { subtags[i].removeSubTag(tag); } 			} 		} 	} 	/** 	 * Find the first nested tag with specified name in a TAG_Compound. * 	 * @param name the name to look for. May be  to look for unnamed tags. * @return the first nested tag that has the specified name. */ 	public Tag findTagByName(String name) { return findNextTagByName(name, null); } 	/** 	 * Find the first nested tag with specified name in a TAG_List or TAG_Compound after a tag with the same name. * 	 * @param name the name to look for. May be  to look for unnamed tags. * @param found the previously found tag with the same name. * @return the first nested tag that has the specified name after the previously found tag. */ 	public Tag findNextTagByName(String name, Tag found) { if (type != Type.TAG_List && type != Type.TAG_Compound) return null; Tag[] subtags = (Tag[]) value; for (Tag subtag : subtags) { if ((subtag.name == null && name == null) || (subtag.name != null && subtag.name.equals(name))) { return subtag; } else { Tag newFound = subtag.findTagByName(name); if (newFound != null) if (newFound == found) continue; else return newFound; } 		} 		return null; } 	/** 	 * Read a tag and its nested tags from an InputStream. * 	 * @param is stream to read from, like a FileInputStream * @return NBT tag or structure read from the InputStream * @throws IOException if there was no valid NBT structure in the InputStream or if another IOException occurred. */ 	public static Tag readFrom(InputStream is) throws IOException { DataInputStream dis = new DataInputStream(new GZIPInputStream(is)); byte type = dis.readByte; if (type == 0) return new Tag(Type.TAG_End, null, null); else return new Tag(Type.values[type], dis.readUTF, readPayload(dis, type)); } 	private static Object readPayload(DataInputStream dis, byte type) throws IOException { switch (type) { case 0: return null; case 1: return dis.readByte; case 2: return dis.readShort; case 3: return dis.readInt; case 4: return dis.readLong; case 5: return dis.readFloat; case 6: return dis.readDouble; case 7: int length = dis.readInt; byte[] ba = new byte[length]; dis.readFully(ba); return ba; case 8: return dis.readUTF; case 9: byte lt = dis.readByte; int ll = dis.readInt; Tag[] lo = new Tag[ll]; for (int i = 0; i < ll; i++) { lo[i] = new Tag(Type.values[lt], null, readPayload(dis, lt)); } 			if (lo.length == 0) return Type.values[lt]; else return lo; case 10: byte stt; Tag[] tags = new Tag[0]; do { stt = dis.readByte; String name = null; if (stt != 0) { name = dis.readUTF; } 				Tag[] newTags = new Tag[tags.length + 1]; System.arraycopy(tags, 0, newTags, 0, tags.length); newTags[tags.length] = new Tag(Type.values[stt], name, readPayload(dis, stt)); tags = newTags; } while (stt != 0); return tags; } 		return null; } 	/** 	 * Read a tag and its nested tags from an InputStream. * 	 * @param os stream to write to, like a FileOutputStream * @throws IOException if this is not a valid NBT structure or if any IOException occurred. */ 	public void writeTo(OutputStream os) throws IOException { GZIPOutputStream gzos; DataOutputStream dos = new DataOutputStream(gzos = new GZIPOutputStream(os)); dos.writeByte(type.ordinal); if (type != Type.TAG_End) { dos.writeUTF(name); writePayload(dos); } 		gzos.flush; gzos.close; } 	private void writePayload(DataOutputStream dos) throws IOException { switch (type) { case TAG_End: break; case TAG_Byte: dos.writeByte((Byte) value); break; case TAG_Short: dos.writeShort((Short) value); break; case TAG_Int: dos.writeInt((Integer) value); break; case TAG_Long: dos.writeLong((Long) value); break; case TAG_Float: dos.writeFloat((Float) value); break; case TAG_Double: dos.writeDouble((Double) value); break; case TAG_Byte_Array: byte[] ba = (byte[]) value; dos.writeInt(ba.length); dos.write(ba); break; case TAG_String: dos.writeUTF((String) value); break; case TAG_List: Tag[] list = (Tag[]) value; dos.writeByte(getListType.ordinal); dos.writeInt(list.length); for (Tag tt : list) { tt.writePayload(dos); } 			break; case TAG_Compound: Tag[] subtags = (Tag[]) value; for (Tag st : subtags) { Tag subtag = st; Type type = subtag.getType; dos.writeByte(type.ordinal); if (type != Type.TAG_End) { dos.writeUTF(subtag.getName); subtag.writePayload(dos); } 			} 			break; } 	} 	/** 	 * Print the NBT structure to System.out */ 	public void print { print(this, 0); } 	private String getTypeString(Type type) { switch (type) { case TAG_End: return "TAG_End"; case TAG_Byte: return "TAG_Byte"; case TAG_Short: return "TAG_Short"; case TAG_Int: return "TAG_Int"; case TAG_Long: return "TAG_Long"; case TAG_Float: return "TAG_Float"; case TAG_Double: return "TAG_Double"; case TAG_Byte_Array: return "TAG_Byte_Array"; case TAG_String: return "TAG_String"; case TAG_List: return "TAG_List"; case TAG_Compound: return "TAG_Compound"; } 		return null; } 	private void indent(int indent) { for (int i = 0; i < indent; i++) { System.out.print("  "); } 	} 	private void print(Tag t, int indent) { Type type = t.getType; if (type == Type.TAG_End) return; String name = t.getName; indent(indent); System.out.print(getTypeString(t.getType)); if (name != null) System.out.print("(\"" + t.getName + "\")"); if (type == Type.TAG_Byte_Array) { byte[] b = (byte[]) t.getValue; System.out.println(": [" + b.length + " bytes]"); } else if (type == Type.TAG_List) { Tag[] subtags = (Tag[]) t.getValue; System.out.println(": " + subtags.length + " entries of type " + getTypeString(t.getListType)); for (Tag st : subtags) { print(st, indent + 1); } 			indent(indent); System.out.println("}"); } else if (type == Type.TAG_Compound) { Tag[] subtags = (Tag[]) t.getValue; System.out.println(": " + (subtags.length - 1) + " entries"); indent(indent); System.out.println("{"); for (Tag st : subtags) { print(st, indent + 1); } 			indent(indent); System.out.println("}"); } else { System.out.println(": " + t.getValue); } 	} 	// For testing purposes. public static void main(String[] args) { try { String filename = "bigtest.nbt"; if (args.length > 0) filename = args[0]; Tag test = Tag.readFrom(new FileInputStream(filename)); FileOutputStream fos = new FileOutputStream("bigtestwrite.nbt"); test.writeTo(fos); fos.close; test = Tag.readFrom(new FileInputStream("bigtestwrite.nbt")); test.print; } catch (FileNotFoundException e) { e.printStackTrace; } catch (IOException e) { e.printStackTrace; } 	} }

If you find bugs: fix this page.

If you dislike this code, maybe the JNBT project is for you. The class above is unrelated to JNBT.