initial refactor copy

examples/src/TcpExamples/TcpSentryScenarioClient.java

+package TcpExamples;
+
+import java.io.*;
+import java.net.*;
+//import java.time.LocalTime; // conversion?
+
+/**
+ * This client program establishes a socket connection to the {@link TcpExample4DispatchServer},
+ * then checks how long it takes to read the single line it expects as a server response.
+ * No fancy footwork here, it is pretty simple and similar to {@link TcpExample3Client}.
+ * 
+ * @see TcpExample4DispatchServer
+ * @see TcpExample4HandlerThread
+ *
+ * @see <a href="../../../src/TcpExamples/TcpExample4TerminalLog.txt" target="blank">TcpExample4TerminalLog.txt</a>
+ * @see <a href="../../../src/TcpExamples/TcpExample4SequenceDiagram.png" target="blank">TcpExample4SequenceDiagram.png</a>
+ * @see <a href="../../../src/TcpExamples/TcpExample4SequenceSketch.png" target="blank">TcpExample4SequenceSketch.png</a>
+ * 
+ * @author Don McGregor
+ * @author Don Brutzman
+ * @author MV3500 class
+ */
+public class TcpSentryScenarioClient
+{
+    /** Default constructor */
+    public TcpSentryScenarioClient()
+    {
+        // default constructor
+    }
+    static String DESTINATION_HOST = "localhost";
+    static int    MAX_LOOP_COUNT   = 4;
+
+    /**
+     * Program invocation, execution starts here
+     * @param args command-line arguments
+     */
+    public static void main(String[] args) {
+        try {
+            System.out.println(TcpSentryScenarioClient.class.getName() + " start, loop " + MAX_LOOP_COUNT + " times");
+            System.out.println("=======================================================");
+            for (int loopCount = 1; loopCount <= MAX_LOOP_COUNT; loopCount++) // loop then exit
+            {
+                System.out.println(TcpSentryScenarioClient.class.getName() + " creating new socket #" + loopCount + "...");
+
+                // 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.This particualar example is interacting
+                // with what it expects is a server that writes a single text
+                // line after 10 sec.
+                long startTime = System.currentTimeMillis();
+
+                // open a socket for each loop
+		Socket socket = new Socket(DESTINATION_HOST, 2317);
+
+                // Setup.  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.
+                InputStream is = socket.getInputStream();
+                Reader isr = new InputStreamReader(is);
+                BufferedReader br = new BufferedReader(isr);
+
+                String serverMessage = br.readLine(); // blocks
+                long readTime = System.currentTimeMillis();
+                long timeLength = readTime - startTime;
+
+                System.out.println(TcpSentryScenarioClient.class.getName() + ": message received from server='" + serverMessage + "'");
+                System.out.println(TcpSentryScenarioClient.class.getName() + ": time msec required for read=" + timeLength);
+                System.out.println("=======================================================");
+                // To push this further, launch multiple copies of TcpExample4Client simultaneously
+            }
+            System.out.println(TcpSentryScenarioClient.class.getName() + " complete");
+            // main method now exits
+        } catch (IOException e) {
+            System.out.println("Problem with " + TcpSentryScenarioClient.class.getName() + " networking:networking:"); // describe what is happening
+            System.out.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.out.println("*** Be sure to stop any other running instances of programs using this port!");
+            }
+        }
+    }
+}

examples/src/TcpExamples/TcpSentryScenarioDispatchServer.java

+package TcpExamples;
+
+import java.io.IOException;
+import java.net.*;
+
+/**
+ * This server program works a bit differently by creating and dispatching a
+ * new thread to handle multiple incoming socket connections, one after another, all running in parallel.
+ * This advanced technique is often used in high=performance high=capacity server programs.
+ * 
+ * @see TcpExample4Client
+ * @see TcpExample4HandlerThread
+ *
+ * @see <a href="../../../src/TcpExamples/TcpExample4TerminalLog.txt" target="blank">TcpExample4TerminalLog.txt</a>
+ * @see <a href="../../../src/TcpExamples/TcpExample4SequenceDiagram.png" target="blank">TcpExample4SequenceDiagram.png</a>
+ * @see <a href="../../../src/TcpExamples/TcpExample4SequenceSketch.png" target="blank">TcpExample4SequenceSketch.png</a>
+ *
+ * @author Don McGregor
+ * @author Don Brutzman
+ * @author MV3500 class
+ */
+public class TcpSentryScenarioDispatchServer
+{
+    /** Default constructor */
+    public TcpSentryScenarioDispatchServer()
+    {
+        // default constructor
+    }
+    /**
+     * Program invocation, execution starts here
+     * @param args command-line arguments
+     */
+    public static void main(String[] args)
+    {
+        try {
+            ServerSocket             serverSocket = new ServerSocket(2317);
+            Socket                   clientConnectionSocket;
+            TcpExample4HandlerThread handlerThread;
+
+            int connectionCount = 0; // state variable
+
+            System.out.println(TcpSentryScenarioDispatchServer.class.getName() + " ready to accept socket connections...");
+            while (true) // infinite loop
+            {
+                clientConnectionSocket = serverSocket.accept(); // block! until connected
+
+                connectionCount++; // unblocked, got another connection
+                
+                // TODO option for the student, provide initial message *to the client*
+                // that we are handing off to a dispatch thread... because that is polite behavior.
+                // Plenty of code in Example3, we instead let our proxy thread
+                // TcpExample4HandlerThread introduce itself to the client.
+                
+                System.out.println("=============================================================");
+                System.out.println(TcpSentryScenarioDispatchServer.class.getName() + ".handlerThread created for connection #" + connectionCount + "...");
+                
+                // hand off this aready-created and connected socket to constructor
+                handlerThread = new TcpExample4HandlerThread(clientConnectionSocket); 
+                handlerThread.start();// invokes the run() method in that object
+                System.out.println(TcpSentryScenarioDispatchServer.class.getName() + ".handlerThread is now dispatched and running, using most recent connection...");
+                
+                // while(true) continue looping, serverSocket is still waiting for another customer client
+            }
+        } 
+        catch (IOException e) {
+            System.out.println("Problem with " + TcpSentryScenarioDispatchServer.class.getName() + " networking:"); // describe what is happening
+            System.out.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.out.println("*** Be sure to stop any other running instances of programs using this port!");
+            }
+        }
+        System.out.println("============================================================="); // execution complete
+    }
+}

examples/src/TcpExamples/TcpSentryScenarioHandlerThread.java

+package TcpExamples;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * <p>
+ * This utility class supports the {@link TcpExample4DispatchServer} program,
+ * handling all programming logic needed for a new socket connection
+ * to run in a thread of its own. This is the server
+ * portion as well, so we artificially invent what happens
+ * if the server can't respond to a connection for several seconds.
+ * </p>
+ * <p>
+ * Warning: do not run this class!  It is created and used automatically by {@link TcpExample4DispatchServer} at run time.
+ * </p>
+ * 
+ * @see TcpSentryScenarioClient
+ * @see TcpSentryScenarioDispatchServer
+ * @see TcpExample4Client
+ * @see TcpExample4DispatchServer
+ * @see TcpExample4HandlerThread
+ *
+ * @see <a href="../../../src/TcpExamples/TcpExample4TerminalLog.txt" target="blank">TcpExample4TerminalLog.txt</a>
+ * @see <a href="../../../src/TcpExamples/TcpExample4SequenceDiagram.png" target="blank">TcpExample4SequenceDiagram.png</a>
+ * @see <a href="../../../src/TcpExamples/TcpExample4SequenceSketch.png" target="blank">TcpExample4SequenceSketch.png</a>
+ * 
+ * @author Don McGregor
+ * @author Don Brutzman
+ * @author MV3500 class
+ */
+public class TcpSentryScenarioHandlerThread extends Thread
+{
+    /** The socket connection to a client */
+    Socket socket;
+    
+    /** 
+     * The thread constructor creates the socket from a ServerSocket, waiting for the client to connect,
+     * and passes that socket when constructing the thread responsible for handling the connection.
+     * 
+     * @param socket The socket connection handled by this thread
+     */
+    TcpSentryScenarioHandlerThread(Socket socket)
+    {
+        this.socket = socket;
+    }
+    /**
+     * Program invocation and execution starts here - but is illegal and unwanted, so warn the unsuspecting user!
+     * @param args command-line arguments
+     */
+    public static void main(String[] args)
+    {
+        System.out.println ("*** TcpExample4HandlerThread is not a standalone executable progam.");
+        System.out.println ("*** Please run TcpExample4DispatchServer instead... now exiting.");
+    }
+    
+    /** Handles one connection. We add an artificial slowness
+     * to handling the connection with a sleep(). This means
+     * the client won't see a server connection response for ten seconds (default).
+     */
+    // @overriding run() method in Java Thread class is deliberate
+    @Override 
+    public void run()
+    {
+        try
+        {
+            System.out.println(TcpSentryScenarioHandlerThread.class.getName() + " starting to handle a thread...");
+            
+            // get the connection output stream, then wait a period of time. 
+            OutputStream os = socket.getOutputStream();
+            PrintStream ps = new PrintStream(os);
+
+            final long TIMEOUT = 2000; // 2000 milliseconds = 2 seconds, 10000 milliseconds = 10 seconds
+            System.out.println(TcpSentryScenarioHandlerThread.class.getName() + " pausing for TIMEOUT=" + TIMEOUT + "ms" + 
+                               " to emulate computation and avoid server-side overload"); 
+            Thread.sleep(TIMEOUT);
+                
+            // ps is the PrintStream is the Java way to use System.print() to pass data along the socket.
+            ps.println("This message was written by the server " + TcpSentryScenarioHandlerThread.class.getName()); // TODO insert socket count here!
+            ps.flush();     // make sure that it indeed escapes current process and reaches the client
+            socket.close(); // all clear, no longer need socket
+            System.out.println(TcpSentryScenarioHandlerThread.class.getName() + " finished handling a thread, now exit.");
+        }
+        catch(IOException | InterruptedException e) // either a networking or a threading problem
+        {
+            System.out.println("Problem with " + TcpSentryScenarioHandlerThread.class.getName() + " networking:"); // describe what is happening
+            System.out.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.out.println("*** Be sure to stop any other running instances of programs using this port!");
+        }
+    }
+}