TCP - Android客户端Java Server

我已经实现了在我的PC上运行的Java TCP服务器，它将接受从运行客户端的Android设备发送的传入消息，也已实现 . 服务器只是从Android设备接收消息并发回答案 . 一切正常，直到我尝试从Android设备发送 second 消息：然后，应用程序崩溃！

但我不知道为什么 . 我使用按钮发送以前写的消息 .

这是服务器线程代码（使用 run() 从main调用该线程）：

public class ServerThread extends Thread {
        ServerSocket serverSocket;

        public ServerThread() {
        }

        public void run() {
            String incomingMsg;

            try {
                System.out.println("Starting socket thread...");

                serverSocket = new ServerSocket(21111);

                System.out
                        .println("ServerSocket created, waiting for incomming connections...");

                Socket socket = serverSocket.accept();

                BufferedWriter out = new BufferedWriter(new OutputStreamWriter(
                        socket.getOutputStream()));
                BufferedReader in = new BufferedReader(new InputStreamReader(
                        socket.getInputStream()));

                while (true) {
                    // System.out.println("Connection accepted, reading...");

                    while ((incomingMsg = in.readLine()) != null && socket.isConnected()) {
                        System.out.println("Message recieved: " + incomingMsg
                                + ". Answering...");

                        // send a message
                        String outgoingMsg = "Message \"" + incomingMsg
                                + "\" recieved on server."
                                + System.getProperty("line.separator");
                        out.write(outgoingMsg);
                        out.flush();

                        System.out.println("Message sent: " + outgoingMsg);
                    }

                    if (socket.isConnected()) System.out.println("Socket still connected");
                    else System.out.println("Socket not connected");
                }

            } catch (Exception e) {
                System.out.println("Error: " + e.getMessage());
                e.printStackTrace();
            }

        }
    }

这是客户端代码 . 我正在使用AsyncTask：

public class MainActivity extends Activity {
    private static final String TAG = "MainActivity";

    private Button sendButton;
    private EditText messageText;
    private String messageToSend;
    private ClientSender clientSender;
    private Context context;
    private Socket socket;

    private static String SERVER_IP = "192.168.1.129";

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

        messageText = (EditText) findViewById(R.id.editTextMessage);
        sendButton = (Button) findViewById(R.id.sendButton);
        context = this.getApplicationContext();
        clientSender = new ClientSender(context);
        socket = null;

        sendButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                messageToSend = messageText.getText().toString()
                        + System.getProperty("line.separator");

                clientSender.execute(messageToSend);

            }
        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    private class ClientSender extends AsyncTask<String, Void, Socket> {
        private Socket socket;
        private String answer;
        private Context context;
        private BufferedWriter out;
        private BufferedReader in;

        public ClientSender(Context context) {
            this.context = context;
            socket = null;
            out = null;
            in = null;
        }

        @Override
        protected Socket doInBackground(String... params) {
            try {
                if (socket == null) {
                    socket = new Socket(SERVER_IP, 21111);

                    out = new BufferedWriter(
                            new OutputStreamWriter(socket.getOutputStream()));
                    in = new BufferedReader(
                            new InputStreamReader(socket.getInputStream()));
                }

                out.write(params[0]);
                out.flush();

                answer = in.readLine() + System.getProperty("line.separator");

                return socket;
            } catch (IOException e) {
                e.printStackTrace();
            }

            return socket;
        }

        protected void onPostExecute(Socket socket) {
            if (socket != null) {
                Toast.makeText(context, answer, Toast.LENGTH_LONG).show();

            } else {
                Toast.makeText(context, "Can't connect to server!",
                        Toast.LENGTH_LONG).show();
            }

        }

    }

}

我不知道发生了什么，但我怀疑套接字连接可能有问题 .