TCP 客户端发送数据，但 TCP 服务器接收到 null

Question

我的应用程序中有一个 TCP 客户端和一个 TCP 服务器类。 客户端发送诸如“1|2|”之类的小字符串或“1|11|”

客户端类

public class TcpClient {


private static final int MAX_DATA_RETRY = 1;
private static final int PING_TIMEOUT = 100;

private ClientThread thread;
private boolean mRun = true;
private PrintWriter mBufferOut;

private String mIPAdress;


private ArrayList<BufferDataItem> messageBuffer = new ArrayList<BufferDataItem>();
private Socket mSocket;

public TcpClient()
{
    thread = new ClientThread();
    thread.start();
}

private class ClientThread extends Thread {

    @Override
    public void run() {

        while(mRun)
        {
            if(messageBuffer.size() <= 0)
                continue;

            BufferDataItem currMessage = messageBuffer.get(0);
            currMessage.retryCount++;
            if(currMessage.retryCount > MAX_DATA_RETRY)
            {
                messageBuffer.remove(0);
                continue;
            }

            try {
                //here you must put your computer's IP address.
                InetAddress serverAddr = InetAddress.getByName(currMessage.ip);



                //Log.e("TCP Client", "C: Connecting...");

                try {
                    if(!serverAddr.isReachable(PING_TIMEOUT))
                    {
                        //only attempt to connect to devices that are reachable
                        messageBuffer.remove(0);
                        continue;
                    }


                    //create a socket to make the connection with the server
                    mSocket = new Socket(serverAddr, TcpManager.SERVER_PORT);

                    //Log.i("TCP Debug", "inside try catch");
                    //sends the message to the server

                    mBufferOut = new PrintWriter(new BufferedWriter(new OutputStreamWriter(mSocket.getOutputStream())), true);

                    String message = currMessage.message;
                    if (mBufferOut != null && !mBufferOut.checkError()) {
                        Log.d("TCP SEND", "PUTTING IN BUFFER!  " + message);
                        mBufferOut.println(message);
                        listener.messageSent(message, currMessage.ip);
                        messageBuffer.remove(0);
                    }
                    mBufferOut.flush();

                }
                catch (ConnectException e) {
                    //Connection refused by found device!
                    //Log.e("TCP", "C: ConnectException   ip = "+currMessage.ip, e);
                    listener.hostUnreachable(currMessage.ip);
                    continue;
                }
                catch (Exception e) {
                    Log.e("TCP", "S: Error", e);
                    listener.messageSendError(e);
                }
                finally {
                    if(mSocket != null)
                        mSocket.close();
                }

            }
            catch (Exception e) {
                Log.e("TCP", "C: Error", e);
                listener.messageSendError(e);
                continue;
            }
        }
    }
}



/**
 * Sends the message entered by client to the server
 *
 * @param message text entered by client
 */
public void sendMessage(String message) {

    BufferDataItem data = new BufferDataItem();
    data.message = message;
    data.ip = mIPAdress;
    messageBuffer.add(data);
}

public void sendMessage(String message, String ip) {
    mIPAdress = ip;
    BufferDataItem data = new BufferDataItem();
    data.message = message;
    data.ip = mIPAdress;
    messageBuffer.add(data);
}


/**
 * Close the connection and release the members
 */
public void stopClient() {
    Log.i("Debug", "stopClient");

    mRun = false;

    if (mBufferOut != null) {
        mBufferOut.flush();
        mBufferOut.close();
    }
    mBufferOut = null;
}

private class BufferDataItem
{
    public String message = "";
    public int retryCount = 0;
    public String ip = "";
}

private OnMessageSent listener = null;

public interface OnMessageSent {
    public void messageSent(String message, String ip);

    public void hostUnreachable(String ip);

    public void messageSendError(Exception e);

}

public void setMessageSentListener(OnMessageSent listener)
{
    this.listener = listener;
}

public void removeMessageSentListener()
{
    this.listener = null;
}

}

服务器类

public class TcpServer {

private ServerThread thread;
private boolean mRun = true;
private boolean mEnd = false;


public TcpServer()
{
    thread = new ServerThread();
    thread.start();
}

private class ServerThread extends Thread {

    @Override
    public void run() {

        try {
            Boolean end = false;
            ServerSocket ss = new ServerSocket(TcpManager.SERVER_PORT);
            while (mRun) {
                //Server is waiting for client here, if needed
                Socket s = ss.accept();
                BufferedReader input = new BufferedReader(new InputStreamReader(s.getInputStream()));
                //PrintWriter output = new PrintWriter(s.getOutputStream(), true); //Autoflush
                String st = input.readLine();
                String remoteIP = s.getRemoteSocketAddress().toString();
                int index = remoteIP.indexOf(":");
                remoteIP = remoteIP.substring(1,index);

                Log.d("TCP READ", "TCP READ: " + st);
                if(st != null)
                    listener.messageReceived(st, remoteIP);
                //output.println("Good bye and thanks for all the fish :)");

                if(mEnd)
                {
                    s.close();
                    mRun = false;
                }
            }

            ss.close();


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

//Declare the interface. The method messageReceived(String message) will must be implemented in the MyActivity
//class at on asynckTask doInBackground
public interface OnMessageReceived {
    public void messageReceived(String message, String ip);
}

private OnMessageReceived listener = null;

public void SetMessageReceivedListener(OnMessageReceived listener)
{
    this.listener = listener;
}

public void RemoveMessageReceivedListener()
{
    this.listener = null;
}

}

这在它运行的前几次运行良好，然后客户端发送“1|11|”并且服务器在 readLine 期间将 st 设置为 null。 String st = input.readLine();

有人有什么建议吗？

Answer 1

我看到服务器在一段时间后没有收到有效数据的两个可能原因。

1. 服务器不会关闭套接字 s，因为 mEnd 从未设置为 true。客户端为每条消息打开一个新的 TCP 连接。服务器为连接创建一个套接字，但它从不关闭套接字，并且连接的服务器端保持打开状态。这是资源泄漏，可能会导致问题。

2. 客户端使用ArrayList<BufferDataItem> messageBuffer。 ArrayList 不是线程安全集合，messageBuffer 用于多个线程。在这里使用synchronizedList 是安全的。请参阅How do I make my ArrayList Thread-Safe? Another approach to problem in Java? 或Concurrent threads adding to ArrayList at same time - what happens?