Java Client/Server don't communicate through Socket/ServerSocket

Question

I have a simple socket/serversocket example that I'm trying to get running, but both the client and the server hang when their BufferedReaders try to read. Here is the code for each:

SERVER

package picturePerfect;
--imports--

public class PictureServer implements Runnable{
static ServerSocket serverSocket;

public static void main(String[] args) throws IOException {
    serverSocket = new ServerSocket(2342);
    Thread firstSessionThread = new Thread(new PictureServer());
    firstSessionThread.start();
}

@Override
public void run() {
    Socket socket = null;
    try {
        socket = serverSocket.accept();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String clientRequest = bufferedReader.readLine();
        System.out.println(clientRequest);
        PrintWriter printWriter = new PrintWriter(socket.getOutputStream(), true);
        printWriter.println("Sent from server!");
    } catch (IOException e) {
        e.printStackTrace();
    }       
}

}

CLIENT

package picturePerfect;
--imports--

public class PictureClient {
    public static void main(String[] args) throws UnknownHostException, IOException, InterruptedException {
        Socket socket = new Socket("localhost", 2342);
        PrintWriter printWriter = new PrintWriter(socket.getOutputStream(), true);
        printWriter.write("Sent from client!");
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String response = bufferedReader.readLine();
        System.out.println(response);
        socket.close();
    }
}

This is the barest I could simplify my code to. I have a sample program that I've been following, which seems nearly exactly the same. This is the sample server and client (that does work):

SAMPLE SERVER

--imports--

public class Server implements Runnable{
    static ServerSocket ss;

    public static void main(String[] args) throws IOException {
        ss = new ServerSocket(3142);
        Thread thread = new Thread(new Server());
        thread.start();
    }

    @Override
    public void run() {
        while ( true ) {
            Socket s = null;

            try {
                s = ss.accept();
                BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
                String operands = br.readLine();
                System.out.println(operands + " was received");
                PrintWriter pw = new PrintWriter(s.getOutputStream(), true);
                pw.println(operands + " right back!");
            } catch ( IOException e ) {
                e.printStackTrace();
            }
        }
    }
}

SAMPLE CLIENT

--imports--

public class Server implements Runnable{
    static ServerSocket ss;


    public static void main(String[] args) throws IOException {
        ss = new ServerSocket(3142);
        Thread thread = new Thread(new Server());
        thread.start();
    }

    @Override
    public void run() {
        while ( true ) {
            Socket s = null;

            try {
                s = ss.accept();
                BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
                String operands = br.readLine();
                System.out.println(operands + " was received");
                PrintWriter pw = new PrintWriter(s.getOutputStream(), true);
                pw.println(operands + " right back!");
            } catch ( IOException e ) {
                e.printStackTrace();
            }
        }
    }
}

I've tried putting the while loop into my server and moving my client and server to the default package, but neither helped. I also tried using read() instead of readLine(), and ending the printWriter's lines with \r\n, but was just as unsuccessful there.

Why does my code hang on readLine(), especially when the sample code doesn't?

Answer 1

What readline() does is wait until it sees a new line character until it returns, hence readLine().

In your client, you do not write a new line. You use:

printWriter.write("Sent from client!");

Instead, write a newline character into the stream using println,

printWriter.println("Sent from client!");

Answer 2

Server expects to read line, so you need to add line separators after your massage. To do this instead of

printWriter.write("Sent from client!");

in client use

printWriter.println("Sent from client!");
//          ^^^^^^^

or

printWriter.write("Sent from client!"+System.lineSeparator());
printWriter.flush();

You will need to flush yourself because autoflush in PrintWriter works only for println, printf, or format, not for write method