I have been trying to learn networking in java and have begun by making a simple client/server program with a simple GUI. The Server simply has a JTextArea and the client has a JTextField, JTextArea and a JButton. The way it is meant to work is that the user on the client side types a message in the JTextField and clicks the JButton(Send). This invokes a sendData method which takes the message the Client typed, puts it in a DatagramPacket and sends the packet to the Server on a predefined port. The Server on startup creates a thread which loops continuously allowing it to passively listen for packets using the DatagramSocket.recieve(DatagramPacket) method. If a packet is recived, it updates the JTextArea of the gui with the data in the packet. However, it seems as though the packets are not reaching the server. I have tested this on a LAN network and it IS working. However, when used over the internet the packets seem to be getting lost. I have tried with two different people who have had their ports forwarded and are sure that they are forwarded. The Client and Server both consist of 3 simple classes. Any help would be greatly appreciated. Sorry for the long description and code dump. Note: I am using UDP for this just because I want to learn it and I know TCP can be better for things like a chat.
Client class of Client:
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
public class Client {
DatagramSocket socket;
Panel panel;
public Client(Panel panel) {
this.panel = panel;
try {
socket = new DatagramSocket();
} catch (SocketException e) {
e.printStackTrace();
panel.textArea.setText("Socket could not be created.");
}
}
public void sendData(byte[] data, InetAddress ipAddress){
DatagramPacket packet = new DatagramPacket(data, data.length, ipAddress, 27015);
try {
socket.send(packet);
panel.textArea.setText("Client: Package being sent to server...");
} catch (IOException e) {
e.printStackTrace();
panel.textArea.setText("Package could not be sent");
}
}
}
Panel class of Client:
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.InetAddress;
import java.net.UnknownHostException;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
public class Panel extends JPanel implements ActionListener {
JButton send;
JTextField textField;
JTextField textArea;
Client client;
InetAddress ipAddress;
public Panel(){
this.setVisible(true);
send = new JButton("Send");
send.addActionListener(this);
send.setVisible(true);
textField = new JTextField();
textField.setVisible(true);
Dimension dim = new Dimension(300,20);
textField.setPreferredSize(dim);
textArea = new JTextField();
Dimension dim2 = new Dimension(300,100);
textArea.setPreferredSize(dim2);
this.add(textField);
this.add(send);
this.add(textArea, FlowLayout.LEFT);
client = new Client(this);
}
public void actionPerformed(ActionEvent e) {
if (e.getSource() == send){
System.out.println("Send was pressed");
String message = textField.getText();
try {
ipAddress = InetAddress.getByName("localhost");
} catch (UnknownHostException e1) {
e1.printStackTrace();
textArea.setText("Hostname could not be resolved");
}
client.sendData(message.getBytes(), ipAddress);
textArea.setText("Client: " + message);
}
}
}
ServerThread class of the Server:
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import javax.swing.JPanel;
public class ServerThread extends Thread{
private DatagramSocket socket;
Panel panel;
public ServerThread(Panel panel) {
this.panel = panel;
try {
socket = new DatagramSocket(27015);
panel.setTextArea("The server has begun listening on port 3659...");
} catch (SocketException e) {
e.printStackTrace();
panel.setTextArea("Server cant open socket and listen on port 3659");
}
}
public void run(){
while(true){
byte[] data = new byte[1024];
DatagramPacket packet = new DatagramPacket(data, data.length);
try {
socket.receive(packet); // waits for packet to arrive
panel.setTextArea("Server: A package was recieved from the Client...");
} catch (IOException e) {
e.printStackTrace();
panel.setTextArea("Socket cant recieve packets");
}
String message = new String(packet.getData());
panel.setTextArea("Client: " + message);
}
}
}
Note: For both the Server and Client, the main class simply makes a new Jframe and a new instance of the panel class and sets that as its contents pane. I did not include the panel class for the Server as it does not include any significant code.
Thanks again.
