UDP simple server client code example

I won’t go into details about the theory of UDP. I will just give you a HelloWorld program about UDP. The code is clear and I hope it will be helpful to the beginners!

Of course, actually, I am just getting started in this area!

First, write the server code. The server binds the local IP and port to listen for access:

package udp;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;

/**
 * UDP service class */
public class UdpServerSocket {
	
	private byte[] buffer = new byte[1024];
	private static DatagramSocket ds = null;
	private DatagramPacket packet = null;
	private InetSocketAddress socketAddress = null;
	
	/**
	 * Test method */
	public static void main(String[] args) throws Exception {
		String serverHost = "127.0.0.1";
		int serverPort = 3344;
		UdpServerSocket udpServerSocket = new UdpServerSocket(serverHost,
				serverPort);
		while (true) {
			udpServerSocket.receive();
			udpServerSocket.response("Hello, have you eaten?");
		}		
	}

	/**
	 * Constructor, bind host and port */
	public UdpServerSocket(String host, int port) throws Exception {
		socketAddress = new InetSocketAddress(host, port);
		ds = new DatagramSocket(socketAddress);
		System.out.println("Server started!");
	}

	/**
	 * Receive data packets. This method will cause thread blocking */
	public final String receive() throws IOException {
		packet = new DatagramPacket(buffer, buffer.length);
		ds.receive(packet);
		String info = new String(packet.getData(), 0, packet.getLength());
		System.out.println("Receive information: " + info);
		return info;
	}

	/**
	 * Send the response packet to the requester */
	public final void response(String info) throws IOException {
		System.out.println("Client address: " + packet.getAddress().getHostAddress()
				+ ",port:" + packet.getPort());
		DatagramPacket dp = new DatagramPacket(buffer, buffer.length, packet
				.getAddress(), packet.getPort());
		dp.setData(info.getBytes());
		ds.send(dp);
	}
}

After running, it prompts that the server runs successfully, the program starts to listen to the port, the receiving method is blocked, and it will proceed only when there is access!

When we write a client to access it, we see that the examples on the Internet all directly create a DatagramSocket object, but in fact we don’t know which port we are using. Here I will specify the port I bind to when I create it. In fact, it is very simple. Just pass a port parameter when initializing the object.

Here when you access the client, the client will print your IP and port!

Take a look at the client code:

package udp;

import java.io.*;
import java.net.*;

/**
 * UDP client program, used to send data to the server and receive the server's response information*/
public class UdpClientSocket {
	private byte[] buffer = new byte[1024];

	private static DatagramSocket ds = null;
	
	/**
	 * Test the client's method of sending packets and receiving response information */
	public static void main(String[] args) throws Exception {
		UdpClientSocket client = new UdpClientSocket();
		String serverHost = "127.0.0.1";
		int serverPort = 3344;
		client.send(serverHost, serverPort, ("Hello, dear!").getBytes());
		byte[] bt = client.receive();
		System.out.println("Server response data: " + new String(bt));
		// Close the connection try {
			ds.close();
		} catch (Exception ex) {
			ex.printStackTrace();
		}
	}

	/**
	 * Constructor, create UDP client */
	public UdpClientSocket() throws Exception {
		ds = new DatagramSocket(8899); // Bind to local port as client }
	
	/**
	 * Send data information to the specified server */
	public final void send(final String host, final int port,
			final byte[] bytes) throws IOException {
		DatagramPacket dp = new DatagramPacket(bytes, bytes.length, InetAddress.getByName(host), port);
		ds.send(dp);
	}

	/**
	 * Receive data sent back from the specified server */
	public final byte[] receive()
			throws Exception {
		DatagramPacket dp = new DatagramPacket(buffer, buffer.length);
		ds.receive(dp);		
		byte[] data = new byte[dp.getLength()];
		System.arraycopy(dp.getData(), 0, data, 0, dp.getLength());		
		return data;
	}
}

Run the program directly to see the effect!

The above is the full content of this article. I hope it will be helpful for everyone’s study. I also hope that everyone will support 123WORDPRESS.COM.

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