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Development resources/Example NBT Class

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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. A condensed documentation is at the bottom of the page.

Note: As of Minecraft weekly version 12w07a, there's a new tag with ID 11 - an "Int Array Tag." Minecraft worlds generated with 12w07a and later will use this tag.

Note 2: Code has been updated to include the new Tag ID 11 "Int Array".

import java.io.DataInputStream;
import java.io.DataOutputStream;
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 <a href="https://github.com/udoprog/c10t/blob/master/docs/NBT.txt">Online NBT specification</a>
 */
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,
        TAG_Int_Array
    }

    /**
     * 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 null 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 null 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 {@link Type} enum.
     * @param name name for the new tag or null to create an unnamed tag.
     * @param value an object that fits the tag type or a {@link Type} to create an empty TAG_List with this list type.
     */
    public Tag(Type type, String name, Object value) {
        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;
        case TAG_Int_Array:
            if (!(value instanceof int[]))
                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 void setValue(Object newValue)
    {
        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;
        case TAG_Int_Array:
            if (!(value instanceof int[]))
                throw new IllegalArgumentException();
            break;
        default:
            throw new IllegalArgumentException();
        }

        value = newValue;
    }

    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;

        int index = subtags.length;

        //For TAG_Compund entries, we need to add the tag BEFORE the end,
        //or the new tag gets placed after the TAG_End, messing up the data.
        //TAG_End MUST be kept at the very end of the TAG_Compound.
        if(type == Type.TAG_Compound) index--;
        insertTag(tag, index);
    }

    /**
     * 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 null 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 null 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();
        Tag tag = null;

        if (type == 0) {
            tag = new Tag(Type.TAG_End, null, null);
        } else {
            tag = new Tag(Type.values()[type], dis.readUTF(), readPayload(dis, type));
        }

        dis.close();

        return tag;
    }

    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;
        case 11:
            int len = dis.readInt();
            int[] ia = new int[len];
            for (int i=0;i<len;i++)
                ia[i] = dis.readInt();
            return ia;
 
        }
        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 {
        DataOutputStream dos = new DataOutputStream(new GZIPOutputStream(os));
        dos.writeByte(type.ordinal());
        if (type != Type.TAG_End) {
            dos.writeUTF(name);
            writePayload(dos);
        }
        dos.writeByte(0);
        dos.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;
        case TAG_Int_Array:
            int[] ia = (int[]) value;
            dos.writeInt(ia.length);
            for (int i=0;i<ia.length;i++)
                dos.writeInt(ia[i]);
            break;
 
        }
    }

    /**
     * Print the NBT structure to System.out
     */
    public void print() {
        print(this, 0);
    }

    private String getTypeString(Type type) {
        return type.name();
    }

    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 if (type == Type.TAG_Int_Array) {
            int[] i = (int[]) t.getValue();
            System.out.println(": [" + i.length * 4 + " bytes]");
 
        } else {
            System.out.println(": " + t.getValue());
        }
    }

   /**
    * Replaces a tag's contents with another.
    * 
    * @param toTag
    * @param fromTag
    */
   public void replaceTag(Tag toTag, Tag fromTag) {
        
        if (toTag.getType() != fromTag.getType())
                throw new RuntimeException("Mismatched types when copying " + toTag.getName() +
                                                                        ", from " + fromTag.getType() + " to " + toTag.getType());
        
        toTag.setValue(fromTag.value);
        toTag.listType = fromTag.listType;
   }
   
   /**
    * Replaces this tags with the contents of this compound or list tag.
    * 
    * @param copyTag The compound or list tag.
    */
   public void replaceTags(Tag copyTag) {
        
        if (getType() != Type.TAG_Compound && getType() != Type.TAG_List)
                throw new RuntimeException("Replacing tags of non-list type: " + getType());
        
        Tag[] subtags = (Tag[]) copyTag.getValue();
        
        for (Tag fromTag : subtags) {
                
                if (fromTag.getType() == Type.TAG_End) {
                        addTag(fromTag);
                        break;
                }
                
                Tag toTag = findTagByName(fromTag.name);
                
                if (toTag == null)
                        addTag(fromTag);
                else
                        replaceTag(toTag, fromTag);
        }
   }
}

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.

Documentation[edit | edit source]

These are the functions and documentation from the class above, in a condensed form. Private functions are not included. The functions are broken up into four categories: Constructors, Data Values, Tag Manaipulation and IO Functions. Hopefully this documentation helps someone understand what is happening, and allows them to use the Tag class. It definitely helped me.


Constructors:

  • Tag(Type type,String name,Tag[] value)
    • Description: Create a new TAG_List or TAG_Compound NBT tag.
    • type: Either TAG_List or TAG_Compound.
    • name: Name for the new tag or null to create an unnamed tag.
    • value: List of tags to add to the new tag.
  • Tag(String name, Type listType)
    • Description: Create a new TAG_List with an empty list. Use {@link Tag#addTag(Tag)} to add tags later.
    • name: Name for this tag or null to create an unnamed tag.
    • listType: Type of the elements in this empty list.
  • Tag(Type type, String name, Object value)
    • Description: Create a new NBT tag.
    • type: Any value from the {@link Type} enum.
    • name: Name for the new tag or null to create an unnamed tag.
    • value: An object that fits the tag type or a {@link Type} to create an empty TAG_List with this list type.


Data Values:

  • getType()
  • getName()
  • getValue()
  • getListType()
  • setValue()


Tag Manipulation:

  • addTag(Tag tag)
    • Description: Add a tag to a TAG_List or a TAG_Compound.
  • insertTag(Tag tag, int index)
    • Description: Add a tag to a TAG_List or a TAG_Compound at the specified index.
  • removeTag(int index)
    • Description: Remove a tag from a TAG_List or a TAG_Compound at the specified index.
    • Return: The removed tag.
  • removeSubTag(Tag tag)
    • Description: 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.
  • findTagByName(String name)
    • Description: Find the first nested tag with specified name in a TAG_Compound.
    • name: The name to look for. May be null to look for unnamed tags.
    • Return: The first nested tag that has the specified name.
  • findNextTagByName(String name, Tag found)
    • Description: Find the first nested tag with specified name in a TAG_List or TAG_Compound after a tag with the same name.
    • name: The name to look for. May be null to look for unnamed tags.
    • found: the previously found tag with the same name.
    • Return: The first nested tag that has the specified name after the previously found tag.


IO Functions:

  • readFrom(InputStream is)
    • Description: Read a tag and its nested tags from an InputStream.
    • 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.
  • writeTo(OutputStream os)
    • Description: Write a tag and its nested tags to an OutputStream.
    • os: Stream to write to, like a FileOutputStream.
    • Throws: IOException if this is not a valid NBT structure or if any IOException occurred.
  • print()
    • Description: Print the NBT structure to System.out.