java - 在 Java 和 Android 中通过套接字获取服务器响应

Question

我正在尝试编写一个 Android 客户端和一个 Java 服务器。

它可以从 Android 客户端向服务器发送消息(如果测试代码被注释掉)，但我无法从服务器向客户端返回响应。

你能帮帮我吗？

这是客户端:

public class MainActivity extends Activity {

private PrintWriter printwriter;
private EditText textField;
private TextView textView;
private Button button;
private String message;
private String serverResponse;
String fromServer;
Socket clientSocket;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    textField = (EditText) findViewById(R.id.editText1);
    textView = (TextView) findViewById(R.id.textView);
    button = (Button) findViewById(R.id.button1);

    final String hostName = "10.111.207.253";
    final int portNumber = 4444;

    button.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            message = textField.getText().toString();
            textField.setText("");

            new Thread(new Runnable() {
                public void run() {
                    try {
                        clientSocket = new Socket(hostName, portNumber);
                        printwriter = new PrintWriter(clientSocket.getOutputStream(),true);
                        printwriter.write(message);

                        // testing only - trying to get the response back from the server
                        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                        while(true) {
                            if ((serverResponse = in.readLine()) != null) {
                                Log.i("server says", serverResponse);
                                break;
                            }
                        }
                        // testing only

                        printwriter.flush();
                        printwriter.close();
                        clientSocket.close();

                    } catch (UnknownHostException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }

                }

            }).start();

            textView.setText("Server: " + serverResponse);
        }
    });
  }
}

这是服务器:

public class MyServer {
    private static ServerSocket serverSocket;
    private static Socket clientSocket;
    private static InputStreamReader inputStreamReader;
    private static BufferedReader bufferedReader;
    private static String message;

    public static void main(String[] args) {
    try {
            serverSocket = new ServerSocket(4444);  
    } catch (IOException e) {
            System.out.println("Could not listen on port: 4444");
    }

    System.out.println("Server started. Listening to the port 4444");

    while (true) {
        try {
            clientSocket = serverSocket.accept();   //accept the client connection
            inputStreamReader = new InputStreamReader(clientSocket.getInputStream());
            bufferedReader = new BufferedReader(inputStreamReader); //get the client message
            message = bufferedReader.readLine();

            if (message != null) {
                System.out.println("Client says: " + message);

                //testing only
                PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
                out.println("response from server");
                //testing only

                inputStreamReader.close();
                clientSocket.close();
            }

        } catch (IOException ex) {
            System.out.println("Problem in message reading");
        }
    }
}

请帮忙!

Answer 1

在刷新客户端的 PrintWriter 之前，您已插入代码以读取来自服务器的回复。您没有使用 println()，因此您传递给构造函数以启用自动刷新的 boolean 值并不适用，如 in the javadoc 所述:

Unlike the PrintStream class, if automatic flushing is enabled it will be done only when one of the println, printf, or format methods is invoked, rather than whenever a newline character happens to be output. These methods use the platform's own notion of line separator rather than the newline character.

这意味着客户端永远不会发送任何东西，因此服务器永远不会收到任何东西。回到客户端，您将永远阻塞等待永远不会到来的回复。

要么使用 printwriter.println() 发送您的消息，要么将 printwriter.flush() 移动到您尝试从服务器读取回复之前。