Java TCPIP检测完整数据包消息

Question

I have developed an application using TCPIP in Java though the use of ServerSockets and Sockets. The application is a Listener that listens for messages arriving at a specified port. When a message arrives it is processed and various things are done. My company has provided a small application that acts as a client that sends a message. Recently, they have extended the small application that that sends multiple messages in one go.

Now, my application that is the Listener does not fully receive the multiple messages. I have tried to increase the default buffer on the ServerSocket and still I don't receive the full message. How can this be debugged? The company has a working version of another application that instantly sends the messages and they are all received instantly. The Listener application receives one message in one go. The below code is a sample:

@Startup
@Singleton
public class Listener {

       private ServerSocket serverSocket;
       private Socket socket;
       @Resource
       private ScheduledExecutorService executor;

       @PostConstruct
       public void init() {
              serverSocket = new ServerSocket(portNumber);
              Runnable runnable = new Runnable() {
                    public void run() {
                       try {
                         if(socket == null) {
                            socket = serverSocket.accept();
                            socket.setKeepAlive(true);
                         }
                         else if(socket.isClosed()) {
                             socket = serverSocket.accept();
                             socket.setKeepAlive(true);
                         }
                         char[] messages = buildMessage(socket.getInputStream());
                        }
                        catch(Exception e) {
                            System.out.println("Exception occurred");
                            e.printStackTrace();
                        }
                    }
              };
              executor.scheduleAtFixedRate(runnable, 0, 0, TimeUnit.SECONDS);
       }

     public char[] buildMessage(InputStream inputStream) throws Exception {
            StringBuilder message = null;
            char[] values = null;
            if(inputStream != null) {
                message = new StringBuilder();
                BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
                int byteRead = bufferedInputStream.read();
                while(byteRead != -1) {
                     char value = (char) byteRead;
                     message.append(value);
                     // check how many bytes available
                     if(bufferedInputStream.available() != 0) {
                         byteRead = bufferedInputStream.read();
                     } 
                     else {
                        // to avoid blocking of data
                        break;
                     }
                }
             }
         }
     }

Answer 1

There is no such thing as a message in TCP.

It is a byte stream, and it can be received in chunks as small as a byte at a time.

If you want messages you must implement them yourself, by reading until you have everything you need.

That may require altering or providing an application protocol such as lines, XML, length-word prefixes, etc., so you know where a message stops.