通过套接字发送的消息未在接收方打印

Question

I am currently learning Java, and I tried to make a simple chat program, which communicates between a server and a client. My problem is that the two programs connect properly to each other, but send messages do not get print out. I do not know whether it is the sending or receiving part. Do not judge my class naming, it is just temporarily.

The client-side part of receiving:

InputStream is = chatterSock.getInputStream();
OutputStream os = chatterSock.getOutputStream();
    Thread readThread = new Thread(() -> {
    while (true) {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            StringBuilder out = new StringBuilder();
            String newLine = System.getProperty("line.separator");
            String line;
            while ((line = reader.readLine()) != null) {
                out.append(line);
                out.append(newLine);
            }

            chatter.print("<p>" + out.toString() + "</p>");

        } catch (IOException ex) {
            chatter.printWarning("Connection lost");
        }

    }

The server-side part is pretty similar.

To send messages I just run

<Socket>.getOutputStream().write(<String>.getBytes());

I already tried some other posts from stackoverflow, but did not find a way that works. Thanks for your help!

Edit: here is the server side:

InputStream is = chatterSock.getInputStream();
OutputStream os = chatterSock.getOutputStream();

Thread readThread = new Thread(() -> {
    while (true) {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            StringBuilder out = new StringBuilder();
            String newLine = System.getProperty("line.separator");
            String line;
            while ((line = reader.readLine()) != null) {
                out.append(line);
                out.append(newLine);
            }
            overlord.print("<p>" + out.toString() + "</p>");

        } catch (IOException ex) {
            overlord.chatterSockList.remove(overlord.chatterSockList.indexOf(chatterSock));
            overlord.printWarning("Connection to " + chatterSock.getInetAddress() + " lost");
            overlord.sendToAll(("User " + username + " disconnected."));
        }
    }

});

Edit: The message gets send here:

sendButton.addActionListener(e -> {

    try {
        chatterSock.getOutputStream().write((messageArea.getText()+"\n").getBytes());
        messageArea.setText("");
    } catch (IOException ex) {
        System.err.println(ex);
        printWarning("Connection lost"); //TODO heartbeat
    }
});

Answer 1

As @Russell Uhl mentions in his comment, a read loop whose termination condition is reader.readLine()) != null is only going to terminate when the output stream is closed.

If the output stream is not closed, that call simply waits for new information, and shall continue to do so indefinitely.

It is also going to wait indefinitely if you don't send over a newline, which is why you were told to add it to your write command.

It would be best to process each line you read separately, rather than trying to append them to a buffer and output them all together. Do the processing inside the loop.

And probably it's also a good idea to add some button to your GUI to terminate the chat. It will disable the rest of the GUI and close the output stream, which in turn will cause the readLine() to return null, and the loop to terminate properly.