使用java编写一个程序，实现一个简单的网络聊天室，支持多个用户同时在线聊天，以及发送文件和图片等功能。

实现网络聊天室需要用到 Socket 编程，下面是一个简单的 Java 代码实现：

import java.io.*;
import java.net.*;
import java.util.*;

public class ChatServer {
    ArrayList<PrintWriter> clientOutputStreams;

    public class ClientHandler implements Runnable {
        BufferedReader reader;
        Socket sock;

        public ClientHandler(Socket clientSocket) {
            try {
                sock = clientSocket;
                InputStreamReader isReader = new InputStreamReader(sock.getInputStream());
                reader = new BufferedReader(isReader);
            } catch(Exception ex) { ex.printStackTrace(); }
        }

        public void run() {
            String message;
            try {
                while ((message = reader.readLine()) != null) {
                    System.out.println("read " + message);
                    tellEveryone(message);
                }
            } catch(Exception ex) { ex.printStackTrace(); }
        }
    }

    public static void main (String[] args) {
        new ChatServer().go();
    }

    public void go() {
        clientOutputStreams = new ArrayList<PrintWriter>();
        try {
            ServerSocket serverSock = new ServerSocket(5000);

            while(true) {
                Socket clientSocket = serverSock.accept();
                PrintWriter writer = new PrintWriter(clientSocket.getOutputStream());
                clientOutputStreams.add(writer);

                Thread t = new Thread(new ClientHandler(clientSocket));
                t.start();
                System.out.println("got a connection");
            }
        } catch(Exception ex) { ex.printStackTrace(); }
    }

    public void tellEveryone(String message) {
        Iterator<PrintWriter> it = clientOutputStreams.iterator();
        while(it.hasNext()) {
            try {
                PrintWriter writer = (PrintWriter) it.next();
                writer.println(message);
                writer.flush();
            } catch(Exception ex) { ex.printStackTrace(); }
        }
    }
}

这段代码实现了一个简单的聊天室，客户端连接到服务器时，服务器会创建一个新的线程来处理客户端的消息。当有消息到来时，服务器会广播消息给所有连接到服务器的客户端。

你还需要编写客户端代码来连接到服务器。以下是一个简单的 Java 客户端代码实现：

import java.io.*;
import java.net.*;
import java.util.*;

public class ChatClient {
    BufferedReader reader;
    PrintWriter writer;
    Socket sock;

    public static void main(String[] args) {
        new ChatClient().go();
    }

    public void go() {
        try {
            sock = new Socket("127.0.0.1", 5000);
            InputStreamReader streamReader = new InputStreamReader(sock.getInputStream());
            reader = new BufferedReader(streamReader);
            writer = new PrintWriter(sock.getOutputStream());
            System.out.println("networking established");
            Thread readerThread = new Thread(new IncomingReader());
            readerThread.start();

            Scanner scanner = new Scanner(System.in);
            while (true) {
                System.out.print("Enter message: ");
                String message = scanner.nextLine();
                writer.println(message);
                writer.flush();
            }
        } catch (Exception ex) { ex.printStackTrace(); }
    }

    public class IncomingReader implements Runnable {
        public void run() {
            String message;
            try {
                while ((message = reader.readLine()) != null) {
                    System.out.println("read " + message);
                }
            } catch (Exception ex) { ex.printStackTrace(); }
        }
    }
}

这段代码实现了一个简单的客户端，它连接到服务器并等待用户输入消息。当用户输入消息时，客户端会将消息发送给服务器。当服务器发送消息时，客户端会读取并将其打印到控制台。

以上代码只是一个简单的实现，你可以根据自己的需求对其进行扩展，例如实现发送文件和图片等功能。