Java Socket聊天应用逻辑异常：连接后无法显示用户名与消息

以下是针对代码中导致无法显示用户名和消息问题的具体修复：

1. 当前客户端无法接收任何消息 #

你的ClientHandler.broadCastMessage方法通过判断排除了当前客户端，导致该用户看不到自己的加入通知和发送的消息。修改后让所有客户端（包括自身）都能收到广播：

public void broadCastMessage(String messageToSend){
    for(ClientHandler clientHandler : clientHandlers){
        try{
            clientHandler.bufferedWriter.write(messageToSend);
            clientHandler.bufferedWriter.newLine();
            clientHandler.bufferedWriter.flush();
        } catch(IOException e){
            closeEverything(socket, bufferedReader, bufferedWriter);
        }
    }
}

2. 消息打印无换行导致视觉上“未显示” #

Client.listenToMessage中使用System.out.print没有换行，消息会堆叠在一起无法正常显示。替换为println：

public void listenToMessage(){
    new Thread(new Runnable(){
        public void run(){
            String messageFromGroupChat;
            try {
                while(socket.isConnected()){
                    messageFromGroupChat = bufferedReader.readLine();
                    System.out.println(messageFromGroupChat);
                }
            } catch (Exception e) {
                closeEverything(socket, bufferedReader, bufferedWriter);
            }
        }
    }).start();
}

3. 输入消息被空格截断 #

Client.sendMessage使用sc.next()只能读取空格前的内容，导致带空格的消息被截断。改为sc.nextLine()读取整行输入：

public void sendMessage(){
    try{
        bufferedWriter.write(userName); 
        bufferedWriter.newLine();
        bufferedWriter.flush();

        Scanner sc = new Scanner(System.in); 
        while(socket.isConnected()){
            String messageToSend = sc.nextLine();
            bufferedWriter.write(userName + ": " + messageToSend);
            bufferedWriter.newLine();
            bufferedWriter.flush();
        }
    } catch(IOException e){
        closeEverything(socket, bufferedReader, bufferedWriter);
    }
}

4. 重复移除客户端引发异常 #

ClientHandler.closeEverything中重复调用removeClientHandler，而run方法的finally块已经执行了该操作，删除重复调用避免异常：

public void closeEverything(Socket socket, BufferedReader bufferedReader, BufferedWriter bufferedWriter ){
    try{
        if(bufferedReader != null){
            bufferedReader.close();
        }
        if(bufferedWriter != null){
            bufferedWriter.close();
        }
        if(socket != null){
            socket.close();
        }
    } catch(IOException e){
        e.printStackTrace();
    }
}

5. 服务器异常无日志无法排查 #

Server.startServer捕获异常后没有任何处理，添加异常打印便于排查服务器启动或连接问题：

public void startServer(){
    try{
        while (!serverSocket.isClosed()) {
            Socket socket = serverSocket.accept();
            System.out.println("A new client has connected");
            ClientHandler clientHandler= new ClientHandler(socket);
            Thread thread = new Thread(clientHandler); 
            thread.start();
            System.out.println("Thread started");
        }
    } catch(IOException e){
        e.printStackTrace();
        closeServerSocket();
    }
}

内容的提问来源于stack exchange，提问作者Bernard Kingsley