Difficulty: 3/10 (just copy and paste, brain needed!)

Lets start off with the client stuff!

****Client****

Ok so first add this java class:
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Once you got that open up client.java and look for

    private void login(String s, String s1, boolean flag)

now in that method look for:

    stream.writeDWord(signlink.uid);

or if you don't have that look for:

    stream.writeDWord(/*signlink.uid*/999999);

now under that add:

    stream.writeString(CreateUID.generateUID());

now look for:

    if(k == 21)

			{

				for(int k1 = socketStream.read(); k1 >= 0; k1--)

				{

					loginMessage1 = "You have only just left another world";

					loginMessage2 = "Your profile will be transferred in: " + k1 + " seconds";

					drawLoginScreen(true);

					try

					{

						Thread.sleep(1000L);

					}

					catch(Exception _ex) { }

				}



				login(s, s1, flag);

				return;

			}

and under that add:

    if(k == 22) {

				loginMessage1 = "Your computer has been UUID banned.";

				loginMessage2 = "Please appeal on the forums.";

				return;

			}

Great now you're done with the client sided part.

Onto server.

****Server****

Open up Connection.java

and near the top you should see:

    public static Collection<String> bannedIps = new ArrayList<String> ();

or something similar. Under those add this:

    public static Collection<String> bannedUid = new ArrayList<String> ();

A few lines under you should see:

    public static void initialize() {

somewhere in that method add:

    banUid();

Then add this:

    public static void unUidBanUser(String name) {

		bannedUid.remove(name);

		deleteFromFile("./Data/bans/UUIDBans.txt", name);	

	}

add this method too:

    static String uidForUser = null;

	public static void getUidForUser(Client c, String name) {

		  File file = new File("./Data/characters/" + name + ".txt");

	        StringBuffer contents = new StringBuffer();

	        BufferedReader reader = null;

	        boolean error = false;

	        try {

	            reader = new BufferedReader(new FileReader(file));

	            String text = null;

	            int line = 0;

	            int done = 0;

	            // repeat until all lines is read

	            while ((text = reader.readLine()) != null && done == 0) {

	            	text = text.trim();

	            	line += 1;

	            	if(line >= 6) {

	            		text = text.trim();

	            		int spot = text.indexOf("=");

	            		String token = text.substring(0, spot);

	            		token = token.trim();

	            		String token2 = text.substring(spot + 1);

	            		token2 = token2.trim();

	            			if(token.equalsIgnoreCase("UUID")) {

	            				uidForUser = token2;

	            				done = 1;

	            			}

	        			}

	            }

	        } catch (FileNotFoundException e) {

	            e.printStackTrace();

	            error = true;

	            c.sendMessage("Could not find the character file "+name+".txt");

	        } catch (IOException e) {

	            e.printStackTrace();

	            error = true;

	            c.sendMessage("A problem occured while trying to read the character file for "+name+".");

	        } finally {

	            try {

	                if (reader != null) {

	                    reader.close();

	                }

	            } catch (IOException e) {

	                e.printStackTrace();

	            }

	        }

	        //System.out.println(macForUser);

	        if(!error) {

	        bannedUid.remove(uidForUser);

			deleteFromFile("./Data/bans/UUIDBans.txt", uidForUser);

			c.sendMessage("@red@Un-UUID banned user "+name+" with the UUID address of "+uidForUser+".");

	        }

	}

Then this:

    public static void addUidToBanList(String UUID) {

		bannedUid.add(UUID);

	}

then this:

    public static boolean isUidBanned(String UUID) {

		return bannedUid.contains(UUID);

	}

then this:

    public static void removeUidFromBanList(String UUID) {

		bannedUid.remove(UUID);

		deleteFromFile("./Data/bans/UUIDBans.txt", UUID);	

	}

next add this method (it reads all the banned UUIDS on server startup):

    public static void banUid() {

		try {

			BufferedReader in = new BufferedReader(new FileReader("./Data/bans/UUIDBans.txt"));

			String data;

			try {

				while ((data = in.readLine()) != null) {

					addUidToBanList(data);

					System.out.println(data);

				}

			} finally {

				in.close();

			}

		} catch (IOException e) {

			e.printStackTrace();

		}

	}

after add this (writes uuids to text file):

    public static void addUidToFile(String UUID) {

		try {

			BufferedWriter out = new BufferedWriter(new FileWriter("./Data/bans/UUIDBans.txt", true));

		    try {

				out.newLine();

				out.write(UUID);

		    } finally {

				out.close();

		    }

		} catch (IOException e) {

			e.printStackTrace();

		}

	}

Great now save and close.

Now open up RS2LoginProtocolDecoder.java.

Once in there add this:

    public static String UUID;

next search for:

    if(uid != 

or something similar. Then under that if statement you should add:

    UUID = readRS2String(rsaBuffer);

if you don't use RSA encryption then add:

    UUID = readRS2String(in);

next search for:

    load(session, uid, name, pass, inC, outC, version);

and change that to:

    load(session, uid, name, pass, inC, outC, version, UUID);

After that look for:

    private synchronized void load(final IoSession session, final int uid, String name, String pass, final ISAACRandomGen inC, ISAACRandomGen outC, int version) {

and change that to:

    private synchronized void load(final IoSession session, final int uid, String name, String pass, final ISAACRandomGen inC, ISAACRandomGen outC, int version, String UUID) {

now in that same method (synchronized void load) look for:

    if(Connection.isNamedBanned(cl.playerName)) {

under that if statement add this:

    if(Connection.isUidBanned(UUID)) {

			returnCode = 22;

		}

Good now you're done with that.
Now lets open commands.java!

add this command:

     if (playerCommand.startsWith("uidban")) {

                try {

                    String playerToBan = playerCommand.substring(7);

                    for (int i = 0; i < PlayerHandler.players.length; i++) {

                        if (PlayerHandler.players[i] != null) {

                            if (PlayerHandler.players[i].playerName.equalsIgnoreCase(playerToBan) && PlayerHandler.players[i].playerRights != 3) {

                                Connection.addUidToBanList(PlayerHandler.players[i].UUID);

                                Connection.addUidToFile(PlayerHandler.players[i].UUID);

                                if (c.playerRights == 3) {

                                    c.sendMessage("@red@[" + PlayerHandler.players[i].playerName + "] has been UUID Banned with the UUI " + PlayerHandler.players[i].UUID);

                                } else {

                                    c.sendMessage("@red@[" + PlayerHandler.players[i].playerName + "] has been UUID Banned.");

                                }

                              PlayerHandler.players[i].disconnected = true;

                            }

                        }

                    }

                } catch (Exception ignored) {

                }

            }

and then add this one to unban:

     if(playerCommand.startsWith("unuidban")) {

            	 String player = playerCommand.substring(9);

            	 Connection.getUidForUser(c, player);

            }

you also might have to add this import:

    import server.Connection;

Ok now onto saving their UUID to their char file.
Open Player.java and add:

    public String UUID = "";

now open Playersave.java and look for:

    characterfile.write("character-rights = ", 0, 19);

			characterfile.write(Integer.toString(p.playerRights), 0, Integer.toString(p.playerRights).length());

			characterfile.newLine();

and right under that add:

    characterfile.write("UUID = ", 0, 7);

			characterfile.write(p.UUID, 0, p.UUID.length());

			characterfile.newLine();

Now for the last part. Open up client.java and look for "void initialize" then in that method add:

    UUID = RS2LoginProtocolDecoder.UUID;

Thats all!

If you use this please thank me! Have a nice day .

[spoiler=FIX!!]
If you get this error:

    unreported exception Exception; must be caught or dec

lared to be thrown

then search for (in the same method where that error is):

    catch(IOException _ex)

		{

			loginMessage1 = "";

and under that add:

    } catch (Exception e) {

			System.out.println("Error while generating uid. Skipping step.");

			e.printStackTrace();

		}