如何使用套接字从服务器发送和接收消息? [英] How to use socket to send and receive message from server?

问题描述

大家好，我有一个任务，我想向服务器发送消息，然后得到回复.我不断收到 failed 1recvfrom failed: EBADF (Bad file descriptor) 错误，我是这个套接字的新手.希望有人可以帮助我.这是我的异步任务:

Hi guys so I have a task where I'm suppose to send a message to a server, and then get a reply back. I keep getting failed 1recvfrom failed: EBADF (Bad file descriptor) error and I'm new to this socket stuff. Hopefully someone can help me out. Here's my async task:

 private class SendDataAsyncTask extends AsyncTask<Void,Void,Void>
    {
        private String reply = "";
        @Override
        protected Void doInBackground(Void... params)
        {
            try {
                Socket socket = new Socket("ip",portNumber);
                PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
                //printWriter.write("hello there");

                printWriter.println("hello there");
                bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                printWriter.flush();
                reply = bufferedReader.readLine();
                if(reply != null && !reply.equals(""))
                {
                    Log.d(SOCKET_TESTING_TAG,"my message is " + reply);
                }
                else
                {
                    Log.d(SOCKET_TESTING_TAG,"no message yet");
                }
                Log.d(SOCKET_TESTING_TAG,"break 3");
                printWriter.close();

            }
            catch (IOException e)
            {
                Log.d(SOCKET_TESTING_TAG,"failed " + e.getMessage());
                e.printStackTrace();
            }
            return null;
        }
        @Override
        public void onPostExecute(Void var)
        {
            tv_response.setText(reply);
        }
    }

• 注意:当我在 printWriter.flush() 之前放置 if 语句来检查空读取行时，我仍然收到错误.
• Note: When I put the if statement to check for the null readline before printWriter.flush() I still get an error.

推荐答案

printWriter.close();

关闭套接字的输入或输出流会关闭另一个流和套接字.删除这两个事件.

Closing the input or output stream of a socket closes the other stream and the socket. Remove both occurrences.

if(bufferedReader.readLine() != null)

这没有意义.如果它不为空，您将丢弃该行，然后阅读下一行.您需要将结果存储到一个变量中.

This doesn't make sense. You are throwing the line away and then reading the next line if it wasn't null. You need to store the result into a variable.

您可能需要使用 printWriter.println() 而不是 printWriter.write().可能对方也在读行，而你没有发送(没有行终止符).

You probably need to use printWriter.println() instead of printWriter.write(). Probably the peer is reading lines too, and you aren't sending one (no line terminator).

如果 reply == null 表示对方已经关闭了连接.不是还没有消息".空字符串可能是协议错误，但也不是尚无消息".

If reply == null it means the peer has closed the connection. Not 'no message yet'. An empty string may be a protocol error but it also is not 'no message yet'.

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