[java] How to detect a remote side socket close?

How do you detect if Socket#close() has been called on a socket on the remote side?

Since the answers deviate I decided to test this and post the result - including the test example.

The server here just writes data to a client and does not expect any input.

The server:

ServerSocket serverSocket = new ServerSocket(4444);
Socket clientSocket = serverSocket.accept();
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
while (true) {
  out.println("output");
  if (out.checkError()) System.out.println("ERROR writing data to socket !!!");
  System.out.println(clientSocket.isConnected());
  System.out.println(clientSocket.getInputStream().read());
        // thread sleep ...
  // break condition , close sockets and the like ...
}

• clientSocket.isConnected() returns always true once the client connects (and even after the disconnect) weird !!
• getInputStream().read()
  • makes the thread wait for input as long as the client is connected and therefore makes your program not do anything - except if you get some input
  • returns -1 if the client disconnected
• out.checkError() is true as soon as the client is disconnected so I recommend this

The method Socket.Available will immediately throw a SocketException if the remote system has disconnected/closed the connection.

You can also check for socket output stream error while writing to client socket.

out.println(output);
if(out.checkError())
{
    throw new Exception("Error transmitting data.");
}