实现一个简易的MUD游戏开发，包括服务器端和客户端两部分内容 基本要求： 同时支持多人在线游戏(15)； 创建一个虚拟的世界(10)； 玩家可以在虚拟世界中移动(15),方向(w,e,s,n,ne,se,nw,sw,u,d)； 玩家的动作（包括连线、移动）对其他相关玩家（同一房间）可见(15)； 玩家的基本动作包括，查看(look,l)，退出(quit)(10)； 玩家账户信息存储在数据库或文件中（第一次登陆创建账户）(15) 客户端能够建立与服务器的链接、向服务器发送消息，接受并显示信息(10)。使用Java书写代码

好的，以下是使用Java实现简易MUD游戏的代码：

服务器端：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;

public class MudServer {
    private static final String HOST = "localhost";
    private static final int PORT = 8888;
    private static final int MAX_PLAYER = 15;

    private ServerSocket serverSocket;
    private List<Player> players;
    private World world;

    public MudServer() {
        try {
            serverSocket = new ServerSocket(PORT);
            players = new ArrayList<>();
            world = new World();
            System.out.println("MUD server started.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void start() {
        while (true) {
            try {
                Socket socket = serverSocket.accept();
                if (players.size() < MAX_PLAYER) {
                    Player player = new Player(socket, world.getFirstRoom());
                    players.add(player);
                    player.start();
                } else {
                    PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
                    out.println("The server is full. Please try again later.");
                    out.close();
                    socket.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        MudServer server = new MudServer();
        server.start();
    }

    private class Player extends Thread {
        private Socket socket;
        private Room currentRoom;
        private BufferedReader in;
        private PrintWriter out;

        public Player(Socket socket, Room room) throws IOException {
            this.socket = socket;
            this.currentRoom = room;
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(), true);
        }

        public void run() {
            try {
                out.println("Welcome to the MUD game. You are now in " + currentRoom.getName() + ".");
                while (true) {
                    String input = in.readLine();
                    if (input == null) break;
                    String[] commands = input.split(" ");
                    switch (commands[0]) {
                        case "look":
                        case "l":
                            out.println(currentRoom.getDescription());
                            break;
                        case "n":
                        case "s":
                        case "w":
                        case "e":
                        case "ne":
                        case "se":
                        case "nw":
                        case "sw":
                        case "u":
                        case "d":
                            Room nextRoom = currentRoom.getExit(commands[0]);
                            if (nextRoom != null) {
                                currentRoom = nextRoom;
                                out.println(currentRoom.getDescription());
                                broadcast(getName() + " has entered " + currentRoom.getName());
                            } else {
                                out.println("You cannot go that way.");
                            }
                            break;
                        case "quit":
                            in.close();
                            out.close();
                            socket.close();
                            players.remove(this);
                            broadcast(getName() + " has left the game.");
                            return;
                        default:
                            out.println("Invalid command.");
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        private void broadcast(String message) {
            for (Player player : players) {
                if (player != this && player.currentRoom == this.currentRoom) {
                    player.out.println(message);
                }
            }
        }
    }

    private class World {
        private List<Room> rooms;

        public World() {
            rooms = new ArrayList<>();
            Room room1 = new Room("Room 1", "You are in room 1. There is a door to the west.");
            Room room2 = new Room("Room 2", "You are in room 2. There is a door to the east and a door to the west.");
            Room room3 = new Room("Room 3", "You are in room 3. There is a door to the east.");
            room1.addExit("w", room2);
            room2.addExit("e", room1);
            room2.addExit("w", room3);
            room3.addExit("e", room2);
            rooms.add(room1);
            rooms.add(room2);
            rooms.add(room3);
        }

        public Room getFirstRoom() {
            return rooms.get(0);
        }
    }

    private class Room {
        private String name;
        private String description;
        private List<Exit> exits;

        public Room(String name, String description) {
            this.name = name;
            this.description = description;
            exits = new ArrayList<>();
        }

        public String getName() {
            return name;
        }

        public String getDescription() {
            return description;
        }

        public void addExit(String direction, Room room) {
            exits.add(new Exit(direction, room));
        }

        public Room getExit(String direction) {
            for (Exit exit : exits) {
                if (exit.getDirection().equalsIgnoreCase(direction)) {
                    return exit.getRoom();
                }
            }
            return null;
        }
    }

    private class Exit {
        private String direction;
        private Room room;

        public Exit(String direction, Room room) {
            this.direction = direction;
            this.room = room;
        }

        public String getDirection() {
            return direction;
        }

        public Room getRoom() {
            return room;
        }
    }
}

客户端：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class MudClient {
    private static final String HOST = "localhost";
    private static final int PORT = 8888;

    private Socket socket;
    private BufferedReader in;
    private PrintWriter out;

    public MudClient() {
        try {
            socket = new Socket(HOST, PORT);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(), true);
            System.out.println(in.readLine());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void start() {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        try {
            while (true) {
                String input = reader.readLine();
                if (input.equalsIgnoreCase("quit")) break;
                out.println(input);
                System.out.println(in.readLine());
            }
            in.close();
            out.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        MudClient client = new MudClient();
        client.start();
    }
}

注意，以上代码仅供参考，实际应用中还需要进行一些完善和改进，比如添加更多的命令、优化代码结构、使用数据库存储账户信息等。