java - 为什么服务器程序在 'String file = br.readLine()' 行卡住？

Question

我是套接字编程新手。我必须编写一个程序，其中客户端接受用户的文件名并将其发送到服务器。服务器读取相应的文件并将其内容发送回客户端。现在我的问题是服务器程序卡住在“String file = br.readLine()”上。当我终止客户端程序时，将执行更多的服务器代码行。如果我在客户端代码末尾注释掉 while 循环，则服务器代码工作得很好(它将数据打印到标准输出)。你能告诉我我的代码有什么问题吗？ 服务器代码:

public class SocketServer {

    public static void main(String[] args) throws Exception{
        System.out.println("Server is started.");
        ServerSocket ss = new ServerSocket(9999);

        System.out.println("Server is waiting for a client.");
        Socket server = ss.accept();

        System.out.println("Client is connected.");

        BufferedReader br = new BufferedReader(new InputStreamReader(server.getInputStream()));
        String file = br.readLine();

        System.out.println("Requested file is: " + file);

        OutputStreamWriter os = new OutputStreamWriter(server.getOutputStream());
        PrintWriter writer = new PrintWriter(os);

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

        String line;
        while((line = fr.readLine()) != null) {
            writer.write(line);
            writer.flush();
            System.out.println(line);
        }
    }
}

客户端代码:

public class SocketClient {

    public static void main(String[] args) throws Exception {
        Scanner in = new Scanner(System.in);
        Socket client = new Socket("localhost", 9999);

        OutputStreamWriter os = new OutputStreamWriter(client.getOutputStream());
        PrintWriter writer = new PrintWriter(os);

        System.out.print("Enter filename: ");
        String file = in.nextLine();

        writer.write(file);
        writer.flush();

        BufferedReader br = new BufferedReader(new InputStreamReader(client.getInputStream()));

        System.out.println("Content of " + file + ":");

        String str;
        while((str = br.readLine()) != null) {
            System.out.print(str);
        }
        System.out.println("File transfer is complete.");
    }

}

Answer 1

br.readLine(); 将等待输入，直到找到换行符。

writer.write(file); 您正在写入不带换行符的文件名。

因此，为了使其正常工作，要么在客户端写入换行符，要么在服务器上逐个字符地读取它。

希望这有帮助。