This question has been asked a lot, but so far, none of the solutions that I applied from previous answers have helped me.

Main goal

I am trying to learn UDP conexions and this is my attempt. I want to have a client ask for a picture at a server via UDP and the server will send it. Then the client will create a file with that information given.

Explanation

My main idea is to ask the server for an image using a "GET" command (not the HTTP, just GET) followed by the name of the image(extension included). Then the client awaits an answer which is the image requested.

Problems

The client waits and answer which does no come

Research

• From another similar question it was a problem that I was using the same PORT for both receive and connect, so I added two ports, receivingPORT and sendingPORT, no results from the Client.

• From other similar questions, It was a Firewall problem. So, on a Win10 machine, I created a new rule for UDP in the Firewall for the ports that I am using for this application, and nothing was received by the Client...

I have checked that the image is loaded into byte[] and the image is sent. But on the Client, nothing is received and stays there waiting for a connection to come through

CODE from Server

public class UDPserver { static DatagramSocket serverUDP; static DatagramPacket packet; static InetAddress address; static byte[] buffer = new byte[65507];//65507 final static int receivingPORT = 6668; final static int sendingPORT = 6669; public static void main(String[] args) throws SocketException, IOException, InterruptedException{ boolean serverActive = true; String order = ""; String file = ""; //Instantiate server serverUDP = new DatagramSocket(receivingPORT); while(serverActive){ //Kind of packet we want to receive packet = new DatagramPacket(buffer, buffer.length); System.out.println("Server awaiting connection..."); //Receive it serverUDP.receive(packet); System.out.println("Received packet from: " + packet.getAddress() + "/" + packet.getPort()); //What does the packet contain? String msg = new String(packet.getData()); address = packet.getAddress(); System.out.println("Order from: " + address + "/" + receivingPORT + " says: " + msg); try{ order = msg.split(" ")[0].trim(); file = msg.split(" ")[1].trim(); } catch (Exception e){ } switch(order){ case("GET"):{ System.out.println("Sending back an image..."); buffer = loadImageFromServer(file); packet = new DatagramPacket(buffer, buffer.length, address, sendingPORT); Thread.sleep(5000); serverUDP.send(packet); System.out.println("Client served"); break; } case("DISCONNECT"):{ buffer = "Server is disconnecting...".getBytes(); packet = new DatagramPacket(buffer, buffer.length, address, sendingPORT); serverUDP.send(packet); serverActive = false; serverUDP.close(); break; } } } } static byte[] loadImageFromServer(String path) { try { System.out.println("Loading path: " + path); //Instantiate a buffer from the image for it BufferedImage img = ImageIO.read(UDPserver.class.getResource(path)); //Create a byte[] stream object to handle the data ByteArrayOutputStream baos = new ByteArrayOutputStream(); //Write the image data into those above with jpg format ImageIO.write(img, "png", baos); //Flush the information baos.flush(); byte[] buffer = baos.toByteArray(); //Write it out on a byte string and return it return buffer; } catch (IOException ex) { Logger.getLogger(UDPserver.class.getName()).log(Level.SEVERE, null, ex.fillInStackTrace()); System.exit(-1); } return null; } } 

CODE client

public class Client { static DatagramSocket clientUDP; static InetAddress address; static DatagramPacket packetSend; static DatagramPacket packetReceive; static int SIZE = 65507; final static int receivingPORT = 6669; final static int sendingPORT = 6668; static byte[] buffer = new byte[SIZE]; static Scanner scan = new Scanner(System.in); public static void main(String[] args) throws SocketException, UnknownHostException, IOException{ boolean clientLoop = true; //Get address address = InetAddress.getByName("localhost"); //Instantiate Client -> UDP clientUDP = new DatagramSocket(); while(clientLoop){ System.out.print("Enter any key and press enter"); scan.next(); //Just to stop the loop //Load the buffer buffer = "GET imagenServidor.png".getBytes(); //buffer = "DISCONNECT".getBytes(); System.out.println("Buffer is ready"); //Arm the packet packetSend = new DatagramPacket(buffer, buffer.length, address, sendingPORT); System.out.println("Packet is armed!"); //Send the packet to the server clientUDP.send(packetSend); System.out.println("Order sent to server"); System.out.println("Waiting an answer"); packetReceive = new DatagramPacket(buffer, buffer.length, address, receivingPORT); clientUDP.receive(packetReceive); System.out.println("Server answered!"); ByteArrayInputStream bais = new ByteArrayInputStream(packetReceive.getData()); BufferedImage image = ImageIO.read(bais); System.out.println(image); } clientUDP.close(); } } 

NOTES

• This is a UDP exercise