套接字编程Java中的数据包丢失

Question

我正在尝试从客户端向服务器发送文件。 以下是我尝试过的代码。 但有时，在传输过程中会丢包。 我不确定我哪里错了。

服务器端代码：

public static void ReadAndWrite(byte[] aByte, Socket clientSocket,
            InputStream inputStream, String fileOutput)
                    throws FileNotFoundException, IOException {
        int bytesRead;
        FileOutputStream fileOutputStream = null;
        BufferedOutputStream bufferedOutputStream = null;
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        try
        {
        fileOutputStream = new FileOutputStream( fileOutput );
        bufferedOutputStream = new BufferedOutputStream(fileOutputStream);
        bytesRead = inputStream.read(aByte, 0, aByte.length);
        System.out.println("The length is "+bytesRead);
        int count = 0;
        do {
            count++;
            byteArrayOutputStream.write(aByte);
            bytesRead = inputStream.read(aByte);
        } while (bytesRead != -1);
        System.out.println("The count is "+count);
        System.out.println("The length is "+byteArrayOutputStream.size());
        bufferedOutputStream.write(byteArrayOutputStream.toByteArray());
        bufferedOutputStream.flush();
        bufferedOutputStream.close();
        clientSocket.close();
        }
        catch(Exception ex)
        {
            Logger.writeLog(ex,Listen.class.getName(), LogType.EXCEPTION);  
            throw ex;
        }

客户端代码：

public  void readByteArrayAndWriteToClientSocket(
            Socket connectionSocket, BufferedOutputStream outToClient, String fileToSend ) throws Exception
    {
        try{
        if (outToClient != null) 
        {
            File myFile = new File(fileToSend);
            System.out.println(myFile.length());
            byte[] byteArray = new byte[(int) myFile.length()];

            FileInputStream fileInputStream = null;

            try {
                fileInputStream = new FileInputStream(myFile);
            } catch (IOException ex) {
                Logger.writeLog(ex, FileUtility.class.getName(), LogType.EXCEPTION);
                throw ex;
            }
            BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);

            try {
                bufferedInputStream.read(byteArray, 0, byteArray.length);
                outToClient.write(byteArray, 0, byteArray.length);
                outToClient.flush();
                outToClient.close();
                connectionSocket.close();


                return;
            } catch (IOException ex) {
                Logger.writeLog(ex, FileUtility.class.getName(), LogType.EXCEPTION);
                throw ex;
            }

        }
        }catch (Exception e) {
            Logger.writeLog(e, getClass().getName(), LogType.EXCEPTION);
            throw e;
        }
    }

Answer 1

没有“数据包丢失”，只有代码中的错误。

在Java中复制流的规范方法如下：

while ((count = in.read(buffer)) > 0)
{
   out.write(buffer, 0, count);
}

如果您事先知道字节数，并且发送方在传输之后必须保持连接打开，则它将变为：

while (total < expected && (count = in.read(buffer, 0, expected-total > buffer.length ? buffer.length : (int)(expected-total))) > 0)
{
   out.write(buffer, 0, count);
   total += count;
}

忘记所有的ByteArrayInput/OutputStreams和多余的副本。 只需从文件中读取并发送到套接字，或从套接字中读取并写入文件即可。

Answer 2

套接字读取方法在获得了您要求的所有字节后将返回，或者在停止从网络接收数据时返回。

由于在任何实际网络中传输经常被中断，因此您需要继续发出读取呼叫，直到拥有所需的字节数为止。

您需要这样的代码：

        char [] buffer = new char[1024];
        int expect = 1000;
        int sofar = 0;
       int chars_read;
       try
       {
          while((chars_read = from_server.read(buffer[sofar])) != -1)
          {
             sofar = sofar + chars_read;
             if (sofar >= expected) break;
          }
       }
       catch(IOException e)
       {
          to_user.println(e);
       }