如何在 java 中从服务器 TCP 获得回复

Question

我的代码只是执行一个简单的任务，即从客户端的控制台向服务器发送文本并接收回复。但是我的代码不起作用。我一直向服务器发送文本，但没有回复发回。我做了几个例子，加上客户给的 2 个数字。我也是这样做的，但我不知道是什么问题。

服务器：

public class Server {
    public static void main(String[] args) {
        try {
            ServerSocket server = new ServerSocket(8);
            Socket client = server.accept();
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToClient = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
            String in = inFromClient.readLine(),out;
            while(in!=null){
                out = in+" from server";
                outToClient.write(out);
                outToClient.newLine();
                outToClient.flush();
            }
            inFromClient.close();
            outToClient.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

客户：

public class Client {
    public static void main(String[] args) {
        try {
            Socket client = new Socket("localhost", 8);
            System.out.println("Connected to server");
            BufferedReader inFromServer = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToServer = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
            Scanner input = new Scanner(System.in);
            String strClient,strServer;
            while(true){
                System.out.print("Client: ");
                strClient = input.nextLine();
                outToServer.write(strClient);
                strServer = inFromServer.readLine();
                System.out.print("Server: ");
                System.out.println(strServer);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

Answer 1

您的代码有几个问题：

您的服务器需要读取一行，而您只写了没有换行符的文本：

正在读取服务器中的一行：inFromClient.readLine()

在客户端中写入不带换行符的文本：outToServer.write(strClient); 将其更改为 outToServer.write(strClient + "\n");

你不刷新客户端的作者。在行 outToServer.write(...);

outToServer.flush();

你只读取了服务器中的 1 行并且没有在循环中再次读取。

编辑： 为了方便起见，我将在此处 post 更正后的代码：（我试过了，效果很好）

客户：

public class Client {
    public static void main(String[] args) {
        try (Socket client = new Socket("localhost", 8);
            BufferedReader inFromServer = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToServer = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
            Scanner input = new Scanner(System.in)) {

            System.out.println("Connected to server");
            String strClient,strServer;

            while(true){
                System.out.print("Client: ");
                strClient = input.nextLine();
                outToServer.write(strClient);
                outToServer.newLine();
                outToServer.flush();
                strServer = inFromServer.readLine();
                System.out.println("Server: " + strServer);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

服务器：

public class Server {
    public static void main(String[] args) {
        try (ServerSocket server = new ServerSocket(8);
            Socket client = server.accept();
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToClient = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()))) {

            String in = inFromClient.readLine(), out;
            while(in != null){
                out = in + " from server";
                outToClient.write(out);
                outToClient.newLine();
                outToClient.flush();
                in = inFromClient.readLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

请注意，此解决方案使用 Javas ARM（自动资源管理）来自动关闭流和套接字。所以这在 java 1.7!

之前是行不通的

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