java - continuous data sending through Socket

Question

I'm writing a Java client/server application. It should allow clients to send text data to the server. This kind of communication should be repeatable many times using the same connection.

I write it like this:

// On a server:
ServerSocket serverSocket = new ServerSocket(port);
Socket socket = serverSocket.accept();
socket.setKeepAlive(true);
BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
if (reader.ready()) {
    for (String line = reader.readLine(); line != null; line = reader.readLine()) {
        // do something with line
    }
}

// On a client:
Socket socket = new Socket(host, port);
socket.setKeepAlive(true);
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
writer.write("Some data from client to server");
writer.flush();

The problem is: I can't read on a server before I close OutputStream on a client. Or I can't open OutputStream on a client again, if it was already closed. How can I do continuous sending and reading of data?

Answer 1

两端需要两个线程，一个线程用于读取数据，另一线程用于写入数据。

Answer 2

The problem is: I can't read on a server before I close OutputStream on a client.

Yes you can. You just can't get to the case where readLine() returns null. It isn't the same thing.

Or I can't open OutputStream on a client again, if it was already closed.

Of course not. You have to create a new Socket.

How can I do continuous sending and receiving of data?

I don't understand the question. The code you posted doesn't attempt that.

Answer 3

If your goal is to send many mesages over the same socket connection, these messages will have to be delimited by an application-level protocol. In other words, you won't be able to rely on any system calls like reader.ready() or reader.readLine() == null to detect the end of the message on te server.

One way to achieve this is to begin each message with its length in characters. The server will then read exactly that number of charecters, and then stop and wait for a new message. Another is to define a special character sequence which concludes each message. The server will react to reading that particular sequence by ending the reading of the current message and returning to the "wait for new message" state. You must ensure that this sequence never appears in the message itself.