Question

I’m having some trouble simulating a connection to my Server Socket, accept seems to continue blocking as it doesn’t “see” the connection.

Here’s some simplified code

@Test
public void testPDMServerThread() {
    try {           
        ServerSocket serverSocket = new ServerSocket(0);        
        int port = serverSocket.getPort();

        Socket clientSocket = new Socket("localhost", port);
        PrintWriter clientRequest = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader serverResponse = new BufferedReader(
                new InputStreamReader(clientSocket.getInputStream()));
        serverThread = new ProducerMonitorServerThread(serverSocket.accept());

        clientRequest.write("Hi!");
        serverThread.start();
        System.out.println("Server says: " + serverResponse.readLine());
        assertEquals("RUNNABLE", serverThread.getState().toString());
    } catch (IOException e) {
    }
}

And here’s the thread where the server should respond

public class ProducerMonitorServerThread extends Thread {

    private Socket socket;

    public ProducerMonitorServerThread(Socket socket) {
        super("PDM");
        this.socket = socket;
    }

    @Override
    public void run() {

        try {
            PrintWriter serverResponse = new PrintWriter(socket.getOutputStream(), true);
            BufferedReader clientRequest = new BufferedReader(
                    new InputStreamReader(socket.getInputStream()));

            String serverInput, clientOutput;

            while((serverInput = clientRequest.readLine()) != null) {
                clientOutput = "Bye!";
                System.out.println("Client says: " +serverInput);
                serverResponse.write(clientOutput);
            }

            serverResponse.close();
            clientRequest.close();
            socket.close();

        } catch (IOException e) {
        }           
    }    
}

It never seems to get past this line which is why I think accept is not seeing the connection

serverThread = new ProducerMonitorServerThread(testServer.accept());

I’m sure there’s something fundamental that I’m just not seeing.

Answer 1

First of all, you should not ignore exceptions like you’re doing.

The problem is not with accept. The problem is that the server uses readLine(), and the client never sends any EOL character, and never closes the socket. So the server is blocked waiting for an EOL to appear in the reader. The same is true for the client: it uses readLine() and the server never sends any EOL.

Use a debugger. It will help you find the cause of such problems.