refactor improvements to handle boolean, int, float, string. now suitable for stealing and reuse!

examples/src/UdpMulticastHttpExamples/UdpReceiver.java

@@ -2,7 +2,6 @@ package UdpMulticastHttpExamples;
 
 import java.io.*;
 import java.net.*;
-import java.nio.ByteBuffer;
 
 /**
  * An example of receiving UDP packets. Since very often both the
@@ -11,6 +10,7 @@ import java.nio.ByteBuffer;
  * 
  * Start this before launching UdpSender.
  * 
+ * @see https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html
  * @author mcgredo
  * @author brutzman
  */
@@ -27,7 +27,6 @@ public class UdpReceiver
     public static void main(String[] args) throws IOException 
     {
         DatagramSocket udpSocket = null;
-        int packetCount = 0;
         
         try
         {
@@ -35,34 +34,54 @@ public class UdpReceiver
             
             // Create a UDP socket
             udpSocket = new DatagramSocket(RECEIVING_PORT);
-            udpSocket.setReceiveBufferSize(1500);
-            udpSocket.setBroadcast(false); // we're just receiving here
+            udpSocket.setReceiveBufferSize(1500); // how many bytes are in buffer?  MTU=1500 is good
+            udpSocket.setBroadcast(false);        // we're just receiving here
             
-            ByteBuffer buffer = ByteBuffer.allocate(1500);
-            DatagramPacket receivePacket = new DatagramPacket(buffer.array(), buffer.capacity());
+            byte[] byteArray = new byte[1500];
+            DatagramPacket receivePacket = new DatagramPacket(byteArray, byteArray.length);
             
-            float first, second;
+            ByteArrayInputStream bais = new ByteArrayInputStream(byteArray);
+            DataInputStream dis = new DataInputStream(bais);
+            
+            boolean       isEvenParity;
+            int           packetCount = 0;
+            int           firstInt;   
+            float         secondFloat;
+            String        thirdString;
+            String        padding;
             
             // You need a new receiving packet to read from every packet received
             while (true)
             {
-                udpSocket.receive(receivePacket);
+                packetCount++; // good practice to increment counter at start of loop, when possible
+                udpSocket.receive(receivePacket); // blocks until packet is received
                 
-                // What happens if you read an integer? Two double values? ***
-                first = buffer.getFloat(); // alternatives: readFloat(); readInt(); dis.readUTF(); 
-                second = buffer.getFloat();
+                // values of interest follow. order and types of what was sent must match what you are reading!
+                firstInt     = dis.readInt();
+                secondFloat  = dis.readFloat();
+                thirdString  = dis.readUTF();
+                isEvenParity = dis.readBoolean();
+                dis.reset(); // clear the input stream after reading
                 
-                buffer.clear();
+                if  (isEvenParity)
+                     padding = " ";
+                else padding = "";
                 
-                System.out.println("first value: " + first + " second value: " + second + " packet count = " + ++packetCount);
+                System.out.println(UdpReceiver.class.getName() + 
+                                      ", first int value="    + firstInt + 
+                                   ", second float value="    + secondFloat + 
+                                   ", third String value=\""  + thirdString + "\"" + // note that /" is literal quote character
+                                          " parity value="    + isEvenParity + padding +
+                                   ", packet counter="        + packetCount);
             }
         }
         catch(IOException e)
         {
             System.err.println("Problem with UdpReceiver, see exception trace:");
             System.err.println(e);
-        } finally {
-            
+        } 
+        finally // clean up prior to exit, don't want to leave behind zombie
+        {
             if (udpSocket != null)
                 udpSocket.close();
         }

examples/src/UdpMulticastHttpExamples/UdpSender.java

@@ -11,12 +11,14 @@ import java.net.*;
  * 
  * Start this before launching UdpReceiver.
  * 
+ * @see https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html
  * @author mcgredo
  * @author brutzman
  */
 public class UdpSender 
 {
-    public static final String          MY_NAME = System.getProperty("user.name");
+    // System properties: https://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html
+    public static final String          MY_NAME = System.getProperty("user.name"); // guru incantation   8)
     public static final int        SENDING_PORT = 1414;
     public static final int      RECEIVING_PORT = 1415;
     public static final String DESTINATION_HOST = "localhost"; // localhost 127.0.0.1 or argon 10.1.105.1
@@ -26,10 +28,15 @@ public class UdpSender
     {
         DatagramSocket udpSocket = null;
         DataOutputStream dos = null;
+        int   packetID = 0;     // counter variable to send in packet
+        float    value = -1.0f; // unreachable value is good sentinel to ensure expected changes occur
+        String message = "Hello MV3500"; // no really
+        String padding = new String();
         
         try
         {
-            System.out.println("UdpSender started...");
+            System.out.println(UdpSender.class.getName() + " shows how to send simple-type values via DataOutputStream");
+            System.out.println(UdpSender.class.getName() + " started...");
             
             // Create a UDP socket
             udpSocket = new DatagramSocket(SENDING_PORT);
@@ -38,42 +45,61 @@ public class UdpSender
             // is a java.io utility that lets us put together an array of binary
             // data, which we put into the UDP packet.
             
-            ByteArrayOutputStream baos = new ByteArrayOutputStream(1500);
-            dos = new DataOutputStream(baos);
+            ByteArrayOutputStream baos = new ByteArrayOutputStream(1500); // how many bytes are in buffer?  MTU=1500 is good
+            dos = new DataOutputStream(baos); // wrapper for writing values, connects both streams
 			
-            // alternatives: writeFloat(17.0f); writeInt(17); writeUTF("\"hello MV3500 no really\"");
-            dos.writeFloat(17.0f);
-            dos.writeFloat(24.0f);
-            byte[] buffer = baos.toByteArray();
-            
             // Put together a packet to send
+            // these types and order of variables must match on sender and receiver
+            byte[] byteArray = baos.toByteArray();
             
             // ID of the host we are sending to
             InetAddress destinationAddress = InetAddress.getByName(DESTINATION_HOST);
             // ID of the host we are sending from
             InetAddress      sourceAddress = InetAddress.getByName("localhost"); // possibly identical if source not modified
             
-            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, destinationAddress, RECEIVING_PORT);
+            DatagramPacket datagramPacket = new DatagramPacket(byteArray, byteArray.length, destinationAddress, RECEIVING_PORT);
        
-            // How fast does this go? Does UDP try to slow it down, or does
-            // this cause network problems? (hint: yes for an unlimited send
-            // rate, unlike TCP). How do you know on the receiving side
-            // that you haven't received a duplicate UDP packet, out of
-            // order packet, or dropped packet?
+            // Hmmm, how fast does UDP stream go? Does UDP effectively slow packets down, or does
+            // this cause network problems? (hint: yes for an unlimited send rate, unlike TCP).
+            // How do you know on the receiving side that you haven't received a
+            // duplicate UDP packet, out-of-order packet, or dropped packet? your responsibility.
             
             for (int index = 1; index <= 100; index++) // avoid infinite send loops in code, they can be hard to kill!
             {
-               udpSocket.send(packet);
-               Thread.sleep(1000); // Send 100, one per second
-               System.out.println(MY_NAME + ": " + sourceAddress + " sent packet " + index + " of 100");
+                packetID++;             // increment counter, prefer using explicit value to index
+                value = 100 - packetID; // countdown
+                boolean isEvenParity = ((packetID % 2) == 0); // % is modulo operator
+                
+                // values of interest follow. order and types of what was sent must match what you are reading!
+                dos.writeInt    (packetID);
+                dos.writeFloat  (value);
+                dos.writeUTF    (message);
+                dos.writeBoolean(isEvenParity);
+                dos.flush(); // sends DataOutputStream to ByteArrayOutputStream
+                byteArray = baos.toByteArray();    // OK so go get the flushed result...
+                datagramPacket.setData(byteArray); // and put it in the packet...
+                udpSocket.send(datagramPacket);    // and send it away. boom gone, nonblocking.
+                
+                if  (isEvenParity)
+                     padding = " ";
+                else padding = "";
+            
+                Thread.sleep(1000); // Send packets at rate of one per second
+                System.out.println(UdpSender.class.getName() + ": " + MY_NAME + " " + sourceAddress + 
+                                   " sent values(" + packetID + ", " + value + ", \"" + message + "\", " + isEvenParity +
+                                   ")" + padding + " as packet #" + index + " of 100");
+                baos.reset(); // clear the output stream after sending
             }
-            System.out.println("UdpSender complete.");
+            System.out.println(UdpSender.class.getName() + " complete."); // all done
+
         }
         catch (IOException | InterruptedException e)
         {
             System.err.println("Problem with UdpSender, see exception trace:");
             System.err.println(e);
-        } finally {
+        } 
+        finally // clean up prior to exit, don't want to leave behind zombies
+        {
             if (udpSocket != null)
                 udpSocket.close();