5 UDP

例子1：

package add.socket.udp;

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



/**
 * @author niusj
 * 先启动2 再启动1
 */
public class UdpUnit1 {
	
	public static void main(String[] args) throws IOException{
		//发送数据
		DatagramSocket datagramSocket = new DatagramSocket();
		
		String str = "Hello World!";
		
		String localAddr = InetAddress.getByName("localhost").toString();
		System.out.println(localAddr);
		
		// 用了public DatagramPacket(byte buf[], int length,InetAddress address,int port)形式
		DatagramPacket packet = new DatagramPacket(
				str.getBytes(), str.length(), InetAddress.getByName("localhost"), 7000);
		
		datagramSocket.send(packet);
		
		//接收数据
		byte[] buffer = new byte[1024];
		DatagramPacket packet2 = new DatagramPacket(buffer, 100);
		datagramSocket.receive(packet2);
		
		System.out.println(new String(buffer, 0, packet2.getLength()));
		
		datagramSocket.close();
	}
	
}

package add.socket.udp;

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UdpUnit2 {
	public static void main(String[] args) throws Exception {
		DatagramSocket socket = new DatagramSocket(7000);
		
		//收信息
		byte[] buffer = new byte[1024];
		DatagramPacket packet = new DatagramPacket(buffer, 1024);
		socket.receive(packet);
		System.out.println(new String(buffer, 0, packet.getLength()));
		
		//返回信息
		String str = "welcome!";
		DatagramPacket packet2 = new DatagramPacket(str.getBytes(),
				str.length(), packet.getAddress(), packet.getPort());
		socket.send(packet2);
		
		socket.close();
		
	}
}