Development resources/Example Minecraft Classic Level Editing Class

To compile and use this class, have your classpath include the path to the LevelEditor.java file and the minecraft-server.jar file.

javac -classpath .:minecraft-server.jar LevelEditor.java

java -classpath .:minecraft-server.jar LevelEditor

or

java -classpath .:minecraft-server.jar LevelEditor new_server_level.dat

import java.io.*;
import java.text.DateFormat;
import java.util.zip.GZIPOutputStream;
import java.util.zip.GZIPInputStream;

public class LevelEditor {
        private com.mojang.minecraft.level.Level level = null;

        LevelEditor() {
        }

        // load from file called filename
        public void load(String filename) {
                FileInputStream fis = null;
                GZIPInputStream gzis = null;
                ObjectInputStream in = null;
                DataInputStream inputstream = null;
                try {
                        fis = new FileInputStream(filename);
                        gzis = new GZIPInputStream(fis);
                        inputstream = new DataInputStream(gzis);
                        if((inputstream.readInt()) != 0x271bb788) {
                                return;
                        }
                        if((inputstream.readByte()) > 2) {
                                System.out.println("Error: Level version > 2, this is unexpected!");
                                return;
                        }
                        in = new ObjectInputStream(gzis);
                        level = (com.mojang.minecraft.level.Level)in.readObject();
                        inputstream.close();
                        in.close();
                        System.out.println("Loading level "+filename+" successful");
                } catch(IOException ex) {
                        ex.printStackTrace();
                } catch(ClassNotFoundException ex) {
                        ex.printStackTrace();
                }
                level.initTransient();
        }

        // save in file called filename
        public void save(String filename) {
                FileOutputStream fos = null;
                GZIPOutputStream gzos = null;
                ObjectOutputStream out = null;
                DataOutputStream outputstream = null;
                try {
                        fos = new FileOutputStream(filename);
                        gzos = new GZIPOutputStream(fos);
                        outputstream = new DataOutputStream(gzos);
                        outputstream.writeInt(0x271bb788);
                        outputstream.writeByte(2);
                        out = new ObjectOutputStream(gzos);
                        out.writeObject(level);
                        outputstream.close();
                        out.close();
                        System.out.println("Saving level "+filename+" successful");
                } catch(IOException ex) {
                        ex.printStackTrace();
                }
        }

        // prints all there is to know about a level, except for the blocks data
        public void printInfo() {
                if (level == null) {
                        return;
                }
                System.out.println("Level info:");
                System.out.println("name: "+level.name);
                System.out.println("creator: "+level.creator);
                System.out.println("createTime: "+(DateFormat.getDateTimeInstance(DateFormat.FULL,DateFormat.FULL).format(level.createTime)));
                System.out.println("width: "+level.width);
                System.out.println("height: "+level.height);
                System.out.println("depth: "+level.depth);
                System.out.println("spawnpoint: ["+level.xSpawn+","+level.ySpawn+","+level.zSpawn+"]");
                System.out.println("spawn rotation: "+level.rotSpawn);
        }

        // safe to use method, return value let's you know if anything was changed
        public boolean setTile(int x, int y, int z, int t) {
                if (
                        x >=0 && x < level.width &&
                        y >=0 && y < level.depth &&
                        z >=0 && z < level.height &&
                        t >= 0 && t <= 37
                ) {
                        if (t == 8 || t == 10) {
                                level.setTile(x,y,z,t);
                        } else if (t >= 0 && t <= 18) {
                                level.setTileNoUpdate(x,y,z,t);
                        }
                        return true;
                }
                return false;
        }

        // gets you the level coordinates from the blocks array index
        public int[] getCoords(int index) {
                int x = index % width;
                index = (index-x) / width;
                int z = index % height;
                int y = (index-z) / height;
                return new int[] {x, y, z};
        }

        public void clearBlocks() {
                for (int i=0; i<level.blocks.length; i++) {
                        level.blocks[i] = 0;
                }
        }

        public void floor(int y, int type) {
                for (int i=0; i<level.width; i++) {
                for (int j=0; j<level.height; j++) {
                        setTile(i,y,j,type);
                }
                }
        }

        public void wallX(int x1, int x2, int z, int y, int height, int type) {
                for (int i=x1; i<=x2; i++) {
                for (int j=y; j<y+height; j++) {
                        if (!setTile(i,j,z,type)) {
                                System.out.println("Warning: a tile got ignored while building a wallX: ["+i+","+j+","+z+"]");
                        }
                }
                }
        }

        public void wallZ(int x, int z1, int z2, int y, int height, int type) {
                for (int i=z1; i<=z2; i++) {
                for (int j=y; j<y+height; j++) {
                        if (!setTile(x,j,i,type)) {
                                System.out.println("Warning: a tile got ignored while building a wallZ: ["+x+","+j+","+i+"]");
                        }
                }
                }
        }

        // substitute all of block type 'from' to 'to' :) returning the number of blocks altered
        public int substitute(byte from, byte to) {
                int count=0;
                for (int i=0; i<level.blocks.length; i++) {
                        if (level.blocks[i] == from) {
                                level.blocks[i] = to;
                                count++;
                        }
                }
                return count;
        }

        public void setSize(int x, int y, int z) {
                level.setData(x, y, z, new byte[x*y*z]);
        }

        public static void main(String [] args) {
                LevelEditor le = new LevelEditor();
                String filename = "server_level.dat";
                if(args.length > 0) {
                        filename = args[0];
                        le.load(filename);
                        if (le.level == null) {
                                System.out.println("Loading level "+filename+" failed");
                                return;
                        }
                } else {
                        le.level = new com.mojang.minecraft.level.Level();
                }
                // Do some fancy editing here

                // set a custom size: 256 wide, 128 high, 512 length
                le.setSize(256, 128, 512);

                // first, let's clear out the field
                le.clearBlocks();

                // add a bunch of walls to fill the lower part of the level
                for (int i=0; i<le.level.width; i++) {
                        le.wallX(0,le.level.height-1,i,0,(int)le.level.getWaterLevel()-1,3);
                }
                // lay the floor
                le.floor((int)le.level.getWaterLevel()-1,2);

                // let the level find a spawn location for us
                le.level.findSpawn();

                // Leave our fingerprint
                le.level.creator = "Minecrafter";
                le.level.name = "A Custom World";
                le.level.createTime = System.currentTimeMillis();

                le.save(filename);
                le.printInfo();
        }
}

To help with getting the correct bytes for different block types, you can also use this class

   public class Blocks 
   {
        public static final byte air                            = (byte)0;
        public static final byte rock                           = (byte)1;
        public static final byte grass                          = (byte)2;
        public static final byte dirt                           = (byte)3;
        public static final byte stone                          = (byte)4;
        public static final byte wood                           = (byte)5;
        public static final byte shrub                          = (byte)6;
        public static final byte blackrock                      = (byte)7;
        public static final byte water                          = (byte)8;
        public static final byte waterstill                     = (byte)9;
        public static final byte lava                           = (byte)10;
        public static final byte lavastill                      = (byte)11;
        public static final byte sand                           = (byte)12;
        public static final byte gravel                         = (byte)13;
        public static final byte goldrock                       = (byte)14;
        public static final byte ironrock                       = (byte)15;
        public static final byte coal                           = (byte)16;
        public static final byte trunk                          = (byte)17;
        public static final byte leaf                           = (byte)18;
        public static final byte sponge                         = (byte)19;
        public static final byte glass                          = (byte)20;
        public static final byte red                            = (byte)21;
        public static final byte orange                         = (byte)22;
        public static final byte yellow                         = (byte)23;
        public static final byte lightgreen                     = (byte)24;
        public static final byte green                          = (byte)25;
        public static final byte aquagreen                      = (byte)26;
        public static final byte cyan                           = (byte)27;
        public static final byte lightblue                      = (byte)28;
        public static final byte blue                           = (byte)29;
        public static final byte purple                         = (byte)30;
        public static final byte lightpurple                    = (byte)31;
        public static final byte pink                           = (byte)32;
        public static final byte darkpink                       = (byte)33;
        public static final byte darkgrey                       = (byte)34;
        public static final byte lightgrey                      = (byte)35;
        public static final byte white                          = (byte)36;
        public static final byte yellowflower                   = (byte)37;
        public static final byte redflower                      = (byte)38;
        public static final byte mushroom                       = (byte)39;
        public static final byte redmushroom                    = (byte)40;
        public static final byte goldsolid                      = (byte)41;
        public static final byte iron                           = (byte)42;
        public static final byte staircasefull                  = (byte)43;
        public static final byte staircasestep                  = (byte)44;
        public static final byte brick                          = (byte)45;
        public static final byte tnt                            = (byte)46;
        public static final byte bookcase                       = (byte)47;
        public static final byte stonevine                      = (byte)48;
        public static final byte obsidian                       = (byte)49;
   }