TcpExample3 server, client and terminal log

CourseExamples/src/TcpExamples/TcpExample3Client.java

+package TcpExamples;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * Before, we always used telnet to connect to the server. Here we are now
+ * writing our own program to do the connection.
+ *
+ * As you will see, when we run this after we start the server we will see the
+ * same string telnet printed, sent by the server. The output at the server will
+ * show different socket pairs for each time we ran it.
+ *
+ * @author mcgredo
+ */
+public class TcpExample3Client {
+
+	// IPv6 String constant for localhost address, similarly IPv4 127.0.0.1
+	public final static String LOCALHOST = "0:0:0:0:0:0:0:1"; 
+
+	public static void main(String[] args) {
+		try {
+			while (true) {
+				System.out.println("TcpExample3Client creating socket...");
+
+				// We request an IP to connect to ("localhost") and
+				// port number at that IP (2317). This establishes
+				// a connection to that IP in the form of the Socket
+				// object; the server uses a ServerSocket to wait for
+				// connections.
+				Socket socket = new Socket(LOCALHOST, 2317); // locohost?
+
+				// Now hook everything up (i.e. set up the streams), Java style:
+				InputStream       is  =     socket.getInputStream();
+				InputStreamReader isr = new InputStreamReader(is);
+				BufferedReader     br = new BufferedReader(isr);
+
+				// Read the single line written by the server. We'd
+				// do things a bit differently if many lines to be read
+				// from the server, instead of one only.
+				String serverMessage = br.readLine();
+				System.out.println("==================================================");
+				System.out.println("Now we're talking!");
+				System.out.println("The message the server sent was " + serverMessage);
+				// socket gets closed, either automatically/silently this code (or possibly by server)
+			} // end while(true)
+		} 
+		catch (IOException e) {
+			System.out.println("Problem with client: "); // describe what is happening
+			System.out.println(e);
+		}
+		// program exit: tell somebody about that
+		System.out.println("client exit");
+	}
+}

CourseExamples/src/TcpExamples/TcpExample3Server.java

+package TcpExamples;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * Very slightly more complex than example1. A complete copy of example 2. The
+ * only thing this does differently is introduce a loop into the response, so
+ * you don't have to restart the program after one response. Also, it prints out
+ * the socket pair the server sees. Run the program via telnet several times and
+ * compare the socket pairs.
+ *
+ * telnet localhost 2317
+ *
+ * If you're sophisticated you can contact the instructor's computer while
+ * running this program.
+ *
+ * telnet [ipNumberOfServerLaptop] 2317
+ *
+ * And have him display the socket pairs he got.
+ *
+ * @author mcgredo
+ */
+public class TcpExample3Server {
+
+	@SuppressWarnings("ConvertToTryWithResources")
+	public static void main(String[] args)
+	{
+		try {
+			// ServerSocket waits for a connection from a client. 
+			// Notice that it is outside the loop; ServerSocket
+			// needs to be made only once.
+
+			System.out.println("TcpExample3Server has started..."); // it helps debugging to put this on console first
+			ServerSocket serverSocket = new ServerSocket(2317);
+
+			// Server is up and waiting (i.e. "blocked" or paused)
+			// Loop, infinitely, waiting for client connections.
+			// Stop the program somewhere else.
+			while (true)
+			{
+				Socket clientConnection = serverSocket.accept(); // block until connected to a client
+				
+				// Now hook everything up (i.e. set up the streams), Java style:
+				OutputStream os = clientConnection.getOutputStream();
+				PrintStream  ps = new PrintStream(os);
+
+				ps.println("This was written by the server"); // this goes back to client!
+
+				// Print some information locally about the Socket
+				// connection. This includes the port and IP numbers
+				// on both sides (the socket pair.)
+				InetAddress localAddress = clientConnection.getLocalAddress();
+				InetAddress remoteAddress = clientConnection.getInetAddress();
+
+				int localPort = clientConnection.getLocalPort();
+				int remotePort = clientConnection.getPort();
+
+				// My socket pair connection looks like this, to localhost:
+				// Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 54876 ))
+				// Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 54881 ))
+				//
+				// Why is the first IP/port the same, while the second set has
+				// different ports?
+				System.out.println("Socket pair: (( " + localAddress.toString() + ", " + localPort + " ), ( "
+						+ remoteAddress.toString() + ", " + remotePort + " ))");
+
+				// Notice the use of flush() and close(). Without
+				// the close() to Socket object may stay open for 
+				// a while after the client has stopped needing this
+				// connection. Close() explicitly ends the connection.
+				ps.flush();
+				clientConnection.close(); // like it or not, you're outta here!
+			}
+		} 
+		catch (IOException e) {
+			System.out.println("problem with networking");
+		}
+	}
+}

CourseExamples/src/TcpExamples/TcpExample3TerminalLog.txt

+run:
+TcpExample3Server has started...
+Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 49239 ))
+Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 49240 ))
+Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 49241 ))
+[etc.]
+
+
+run:
+TcpExample3Client creating socket...
+==================================================
+Now we're talking!
+The message the server sent was This was written by the server
+TcpExample3Client creating socket...
+==================================================
+Now we're talking!
+The message the server sent was This was written by the server
+TcpExample3Client creating socket...
+==================================================
+Now we're talking!
+The message the server sent was This was written by the server
+TcpExample3Client creating socket...
+==================================================
+[etc.]