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assignments/src/MV3500Cohort2020JulySeptember/homework2/Mahan/Mahan_Client.java

+package MV3500Cohort2020JulySeptember.homework2.Mahan;
+
+import java.io.*;
+import java.net.*;
+/**
+ *
+ * @author Bill
+ */
+public class Mahan_Client {
+
+    // 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) {
+        
+        // Local vars/fields
+        Socket socket;
+        InputStream is;
+        InputStreamReader isr;
+        BufferedReader br;
+        String serverMessage;
+        Integer count = 0;
+        
+        OutputStream os;
+        PrintStream ps;
+        
+        
+        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 a Socket
+                // object; the server uses a ServerSocket to wait for
+                // connections.
+                socket = new Socket(LOCALHOST, 2317); // locohost?
+
+                // Now hook everything up (i.e. set up the streams), Java style:
+                is = socket.getInputStream();
+                isr = new InputStreamReader(is);
+                br = new BufferedReader(isr);
+                
+
+                // Read a single line written by the server. We'd
+                // do things a bit differently if there were many lines to be read
+                // from the server instead of one only.
+                serverMessage = br.readLine();
+                System.out.println("==================================================");
+                System.out.println("'Knock, knock,' says the MahanClient.");
+                System.out.println("The MahanServer responds by saying: '" + serverMessage + "'");
+                System.out.println("A frustrated MahanClient responds, 'Answer your door! I have knocked "+ count +" times.");
+                count++;
+                // socket gets closed, either automatically/silently by this code (or possibly by the server)
+                
+                
+                // Now hook everything up (i.e. set up the streams), Java style:
+                os = socket.getOutputStream();
+                ps = new PrintStream(os);
+                ps.println("This message was produced by the MahanClient."); // this gets sent back to client!
+                
+                ps.flush();
+                
+                
+                
+            } // end while(true)
+        } catch (IOException e) {
+            System.err.println("Problem with TcpExample3ServerClient networking:"); // describe what is happening
+            System.err.println("Error: " + e);
+            
+            // Provide more helpful information to user if exception occurs due to running twice at one time
+            if (e instanceof java.net.BindException) {
+                System.err.println("*** Be sure to stop any other running instances of programs using this port!");
+            }
+        } finally {
+        
+            // program exit: tell somebody about that
+            System.out.println("\nclient exit");
+        }
+    }
+}

assignments/src/MV3500Cohort2020JulySeptember/homework2/Mahan/Mahan_Server.java

+package MV3500Cohort2020JulySeptember.homework2.Mahan;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ *
+ * @author Bill
+ */
+public class Mahan_Server {
+
+    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);
+            OutputStream os;
+            PrintStream ps;
+            InetAddress localAddress, remoteAddress;
+            
+            InputStream is;
+            InputStreamReader isr;
+            BufferedReader br;
+            String clientMessage;
+            int localPort, remotePort;
+
+            // Server is up and waiting (i.e. "blocked" or paused)
+            // Loop, infinitely, waiting for client connections.
+            // Stop the program somewhere else.
+            while (true) { 
+                
+                // block until connected to a client
+                try (Socket clientConnection = serverSocket.accept()) {
+                    
+                    // Now hook everything up (i.e. set up the streams), Java style:
+                    os = clientConnection.getOutputStream();
+                    ps = new PrintStream(os);
+                    ps.println("Go away!"); // this gets sent back to client!
+                    
+                    // Print some information locally about the Socket connection.
+                    // This includes the port and IP numbers on both sides (the socket pair).
+                    localAddress = clientConnection.getLocalAddress();
+                    remoteAddress = clientConnection.getInetAddress();
+                    localPort = clientConnection.getLocalPort();
+                    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("TcpExample3Server socket pair: (( " + localAddress.toString() + ", " + localPort + " ), ( "
+                            + remoteAddress.toString() + ", " + remotePort + " ))");
+                    
+                    // Notice the use of flush() and try w/ resources. Without
+                    // the try w/ resources the Socket object may stay open for
+                    // a while after the client has stopped needing this
+                    // connection. try w/ resources explicitly ends the connection.
+                    
+                                    // Now hook everything up (i.e. set up the streams), Java style:
+                is = clientConnection.getInputStream();
+                isr = new InputStreamReader(is);
+                br = new BufferedReader(isr);
+                
+
+                // Read a single line written by the server. We'd
+                // do things a bit differently if there were many lines to be read
+                // from the server instead of one only.
+                clientMessage = br.readLine();
+                System.out.println("==================================================");
+                System.out.println("Now we're talking!");
+                System.out.println("The message the server sent was: '" + clientMessage + "'");
+//                System.out.println("This was the "+ count +" connection.");
+                    
+                    
+                    
+                    ps.flush();
+                    // like it or not, you're outta here!
+                }
+            }
+        } catch (IOException e) {
+            System.err.println("Problem with TcpExample3Server networking: " + e);
+
+            // Provide more helpful information to user if exception occurs due to running twice at one time
+            if (e instanceof java.net.BindException) {
+                System.err.println("*** Be sure to stop any other running instances of programs using this port!");
+            }
+        }
+    }
+}

assignments/src/MV3500Cohort2020JulySeptember/homework2/Mahan/README.md

@@ -10,3 +10,11 @@ References include
 * [assignments source subdirectories](../../../../../assignments/src) show examples from previous cohorts. 
 
 Questions and innovation are always welcome, good luck!
+
+Coded two classes:
+MahanServer
+MahanClient
+
+1. Run the MahanServer once
+2. Run the MahanClient as many times as you want
+3. Enjoy the messages from the two consoles 
\ No newline at end of file